A Group of Scientists Suggest that Plants Feel Pain

plants

For years, scientists are baffled by the question of whether plants can feel pain or not. A team of scientists from Tel Aviv University may have the answer to that question, as they discovered that some  plants can emit a high-frequency distress sound  when in environmental stress. 

Study suggests plants can feel pain.

The team of researchers tested tobacco plants and tomato plants by not watering them and by cutting off their stems. They then recorded their response with a microphone that was placed ten centimeters away. 

In both cases, the scientists found that the plants began to emit ultrasonic sounds that were between 20 and 100 kilohertz, which they believed could convey their distress to other organisms and plants within the vicinity. When the stem of a tomato plant was cut, the researches found it emitted 25 ultrasonic distress sounds over the course of an hour, according to the study that was published in  Live Science.  

The tobacco plants that had its stem cut sent out 15 distress sounds. When the team of scientists deprived each plant of water, the tomato plants emitted even more distress sounds, increasing to 35 in one hour, while the tobacco plants made 11. The plants also seemed to respond with the different intensities of sound to different sources of environmental stress. They observed that the tobacco plants let out louder sound when they were not watered than when they had their stems cut. 

The plants that did not experience any environmental stress, damage, or threat released less than one ultrasonic sound per hour.

Do plants feel pain?

The group of scientists wrote in their paper that these findings can alter the way that we think about the plant kingdom, which has been considered to be almost silent and not given much thought. The researchers used the data that they had gathered in a machine learning model to be able to predict the different frequency of sound that plants may emit under other conditions like heavy rain or wind. 

The team scientists believe that listening to different types of sounds that are emitted by plants could help with precision agriculture, and it can allow farmers to identify any potential issue with their crops. 

Last year, another study found that some plants registered pain after their leaves were touched and plucked, which eventually caused the release of foul-tasting chemicals across the leaves. It is believed that the chemical is released to ward off insects. 

Response to environmental stress

The smell that we usually associate with freshly cut grass is actually a chemical distress call. It is used by plants to beg critters to save them from attack. To protect themselves, plants employ numerous  molecular responses . These chemical communications can be used to poison an enemy, alert the surrounding plants to potential dangers, or attract helpful insects to perform needed services. 

There is also  evidence  that plants can hear themselves being eaten. A group of researchers at the University of Missouri-Columbia found that plants can understand and respond to the chewing sounds that are made by caterpillars while they are eating them. As soon as the plants hear the noises, they automatically respond with numerous defense mechanisms.  

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Do Plants Feel Pain? A Primer on Plant Neurobiology

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woman in field holding ears

Few moments evoke a sense of summer like catching a whiff of freshly cut grass. For many people, it's a pleasant sign that warmer temperatures are here to stay. However, for the grass, this scent signals an entirely different story.

The smell we associate with freshly cut grass is actually a chemical distress call, one used by plants to beg nearby critters to save them from attack (usually it's an affront by insects, but in this case, it's lawnmower blades). This defense response beckons the question: Do plants feel pain ?

The answer is a bit complicated because they don't feel pain like us humans do, but some plant scientists posit that may be feel pain in their own way. Let's dive into some plant neurobiology to figure out how these multicellular organisms might be experiencing pain.

Nervous Systems

Chemical defenses, screaming cucumbers, plant consciousness may be a real thing.

Pain perception is typically associated with living organisms that possess a nervous system, which includes specialized sensory receptors, neurons and regions of the brain responsible for processing sensory information. Only, plants don't have a brain or nervous system — but they do exhibit complex signaling and communication systems that allow them to respond to their environment.

Plants use a variety of chemical and electrical signals to sense changes in light, gravity, temperature and touch. They can also respond to external stimuli by growing toward or away from them, adjusting their root and shoot growth and producing defense compounds against predators. These responses are managed through intricate biochemical pathways and plant-signaling molecules like hormones.

While plants are not chatty in a conventional human way, they use chemical communication to protect themselves. When danger strikes — whether it's landscaping equipment, a hungry caterpillar or other living organisms — plants can't lift their roots and run. They must fight where they stand. To protect themselves, plants employ a volley of molecular responses.

These chemical communications can be used to poison an enemy, alert surrounding plants to potential dangers or attract helpful insects to perform needed services [source: Krulwich ].

Sometimes, a plant's molecular defense plays double duty. For example, plants that produce caffeine use the chemical as self-defense, but it also gives bees a caffeine buzz. The caffeinated bees treat the plant like it's the corner coffee shop, returning again and again and leaving their pollination services as payment.

A Complex Biological Network

As they grow, plants can alter their trajectories to avoid obstacles or reach for support with their tendrils. This activity stems from a complex biological network distributed through the plants' roots, leaves and stems that helps them propagate, grow and survive. Trees in a forest, for instance, can warn their relatives of insect attacks.

One scientist injected fir trees with radioactive carbon isotopes; within a few days, the carbon had been sent from tree to tree until every tree in the 30-meter-square area was connected. The scientist learned that the mature trees "communicated" to the network to share nutrients through their root systems to feed nearby seedlings until they were tall enough to take in light for themselves [source: Pollan ].

While we're on the subject of unique communication methods, let's take a look at some mildly unsettling scientific findings.

According to researchers at the Institute for Applied Physics at the University of Bonn in Germany, plants release gases that are the equivalent of crying out in pain. Using a laser-powered microphone , researchers have picked up sound waves produced by plants releasing gases when cut or injured.

Although not audible to the human ear, the secret voices of plants have revealed that cucumbers scream when they are sick, and flowers whine when their leaves are cut [source: Deutsche Welle ]. And it's not just cucumbers that are making their voices heard.

Stressed Tomato Plants

For a 2019 study published in the journal Cell, researchers from Tel Aviv University placed microphones near tomato and tobacco plants that were dehydrated or damaged. They were able to detect ultrasonic sounds emitted by the plants from a distance of about four inches. These sounds ranged from 20 to 100 kilohertz, potentially detectable by certain organisms from several meters away.

However, you won't hear these screams while chilling out in the living room near your favorite basil plant because these sounds occur at ultrasonic frequencies beyond human hearing range. When adjusted to frequencies audible to human ears, these bursts of sound caused by stress resemble the sound of someone tap dancing on a field of bubble wrap.

While these ultrasonic bursts are beyond human hearing, they could potentially be perceived by mammals, insects and other plants in their natural environments, prompting corresponding reactions.

Chewing Sounds Put Plants on High Alert

In a macabre turn of events, there's also evidence that plants can hear themselves being eaten. Researchers at the University of Missouri-Columbia found that plants understand and respond to chewing sounds made by caterpillars munching on them. As soon as the plants hear the noises, they respond with several defense mechanisms [source: Feinberg ].

For some researchers, evidence of these complex communication systems — emitting noises via gas when in distress — signals that plants can feel some type of pain. Others argue that there cannot be pain without a brain and nervous system to register the feeling. But before you rethink your veggie medley, know that you're not engaging in any botanical torture because these plants are likely not experiencing pain like land animals, sea creatures or other animals.

Still, more scientists surmise that plants can exhibit intelligent behavior without possessing a brain or conscious awareness [source: Pollan ].

Research has revealed surprising insights into plant behavior, challenging assumptions about their capabilities. Plants, like the Mimosa pudica , can be anesthetized with substances like ether or lidocaine, causing them to stop responding to stimuli and suppressing their electrical activity.

This has sparked questions about whether this "sleep" state implies awareness or consciousness in plants. A small group of researchers, including Paco Calvo at the University of Murcia, are taking this idea seriously.

Plants exhibit sophisticated abilities, sensing and reacting to various environmental aspects, engaging in communication and complex interactions with other species. While some behaviors are instinctual, others might hint at a form of cognition. Calvo's work focuses on identifying factors indicative of cognitive behavior in plants, such as flexibility, prediction and goal-directedness.

This article was updated in conjunction with AI technology, then fact-checked and edited by a HowStuffWorks editor.

Plants Feel Pain FAQ

Do plants feel pain, do plants scream when you cut them, do plants make noises when you eat them, lots more information, related articles.

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  • Deutsche Welle. "When Plants Say 'Ouch.'" May 2, 2002. (Aug. 1, 2014) http://www.dw.de/when-plants-say-ouch/a-510552-1
  • Feinberg, Ashley. "Nice Try, Vegans: Plants Can Actually Hear Themselves Being Eaten." Gizmodo. July 3, 2014. (Sept. 8, 2014) http://gizmodo.com/nice-try-vegans-plants-can-actually-hear-themselves-b-1599749162
  • Krulwich, Robert. "Plants Talk. Plants Listen. Here's How." NPR. April 29, 2014. (Aug. 1, 2014) http://www.npr.org/blogs/krulwich/2014/04/29/307981803/plants-talk-plants-listen-here-s-how
  • Pollan, Michael. "The Intelligent Plant." The New Yorker. Dec. 23, 2013. (Aug. 1, 2014) http://www.newyorker.com/magazine/2013/12/23/the-intelligent-plant

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Debunking a myth: plant consciousness

Jon mallatt.

1 The University of Washington WWAMI Medical Education Program at The University of Idaho, Moscow, ID 83844 USA

Michael R. Blatt

2 Laboratory of Plant Physiology and Biophysics, Bower Building, University of Glasgow, Glasgow, G12 8QQ UK

Andreas Draguhn

3 Institute for Physiology and Pathophysiology, Medical Faculty, University of Heidelberg, 69120 Heidelberg, Germany

David G. Robinson

4 Centre for Organismal Studies, University of Heidelberg, 69120 Heidelberg, Germany

Lincoln Taiz

5 Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Cruz, CA 95064 USA

Associated Data

Not applicable.

Claims that plants have conscious experiences have increased in recent years and have received wide coverage, from the popular media to scientific journals. Such claims are misleading and have the potential to misdirect funding and governmental policy decisions. After defining basic, primary consciousness, we provide new arguments against 12 core claims made by the proponents of plant consciousness. Three important new conclusions of our study are (1) plants have not been shown to perform the proactive, anticipatory behaviors associated with consciousness, but only to sense and follow stimulus trails reactively; (2) electrophysiological signaling in plants serves immediate physiological functions rather than integrative-information processing as in nervous systems of animals, giving no indication of plant consciousness; (3) the controversial claim of classical Pavlovian learning in plants, even if correct, is irrelevant because this type of learning does not require consciousness. Finally, we present our own hypothesis, based on two logical assumptions, concerning which organisms possess consciousness. Our first assumption is that affective (emotional) consciousness is marked by an advanced capacity for operant learning about rewards and punishments. Our second assumption is that image-based conscious experience is marked by demonstrably mapped representations of the external environment within the body. Certain animals fit both of these criteria, but plants fit neither. We conclude that claims for plant consciousness are highly speculative and lack sound scientific support.

Introduction

The idea that plants are conscious is increasingly promoted by a vocal handful of botanists (A. Nagel 1997 ; Calvo 2017 ; Calvo et al. 2017 ; Gagliano 2017 , 2018 ; Calvo and Trewavas 2020 ; Trewavas et al. 2020 ). This continues despite rebuttals of the claim by mainstream plant biologists (Alpi et al. 2007 ; Robinson et al. 2018 ; Taiz et al. 2019 , 2020 ), and the idea has received widespread coverage in the popular press and media ( https://www.newyorker.com/magazine/2013/12/23/the-intelligent-plant ; https://e360.yale.edu/features/are_trees_sentient_peter_wohlleben ; https://www.youtube.com/watch?v=Xm5i53eiMkU ; https://www.wnycstudios.org/podcasts/radiolab/articles/smarty-plants ). Proponents of plant consciousness also champion the concepts of “plant neurobiology” and “plant intelligence” (Brenner et al. 2006 ). Plants do not have neurons, but plant-neurobiology proponents claim they have analogous structures. In many cases, these proponents treat plant intelligence and plant consciousness with little distinction, using the same arguments for both attributes (Trewavas and Baluska 2011 ; Leopold 2014 ; Trewavas 2016 ; Reber and Baluška 2020 ; Trewavas et al. 2020 ).

Here, we disentangle the “intelligence” concept (Chamovitz 2018 ) from the “consciousness” concept to focus on the claims that are explicitly concerned with plant consciousness. We list 12 such claims (Table ​ (Table1) 1 ) and analyze them individually. We then present an alternate hypothesis of which organisms have consciousness, a hypothesis that fits the widespread scientific view that consciousness is an emergent property arising from complex networks of neurons (Feinberg and Mallatt 2020 ). We provide many new arguments against plant consciousness, plus new angles on past arguments.

Claims for plant consciousness

1. Each living cell is conscious.
2. Consciousness in plants is indicated because they sense environmental changes and respond adaptively, integrating information for goal-directed behaviors, and making decisions along the way.
3. Membrane potentials and electrical signals are similar in plants and animals, in ways that allow consciousness.
4. Action potentials and other electrical signals for communication propagate, neuron-like, along phloem elements.
5. Plants, like animals with neurons, use electrical signals to integrate information for consciousness.
6. Plants have a brain (“command center”) in the root.
7. Plants show proactive, anticipatory behavior.
8. Plants show classical associative learning, which indicates consciousness.
9. Plants communicate with each other in a purposeful manner and, hence, have conscious self-recognition.
10. Detailed hypotheses, predictions and models can substitute for hard evidence of plant consciousness.
11. Plants show affective (emotional) consciousness.
12. Plants have image-based consciousness, based on internal representations.

Definition of consciousness

Consciousness is a difficult topic, and its constructs and definition are much debated (https://en.wikipedia.org/wiki/Category:Consciousness#:). Even so, considerable agreement is achieved when it is stripped to its fundamentals. Both we and the proponents of plant consciousness focus on the most basic type, called phenomenal or primary consciousness (Block 1995 ; Edelman et al. 2011 ; Feinberg and Mallatt 2016a , b ; Calvo 2017 ; Mallatt and Feinberg 2020 ). Primary consciousness means having any type of experiences or feelings, no matter how faint or fleeting (Revonsuo 2006 : p. 37). Such a basal type of consciousness was most succinctly characterized by Thomas Nagel ( 1974 ) as “something it is like to be” when he asked, “What is it like to be a bat?” It means having a subjective or first-person point of view, and what is sometimes called sentience (from Latin sententia , “feeling”). This primary form of consciousness does not involve the ability to reflect on the experiences, the self-awareness that one is conscious, self-recognition in a mirror, episodic memory (the recollection of past personal experiences that occurred at a particular time and place), dreaming, or higher cognitive thought, all of which are higher types of consciousness (Feinberg and Mallatt 2018 : p. 131). All conscious organisms have primary consciousness, but only some of them have evolved higher consciousness on that base.

Restricting our discussion to primary consciousness lets us focus on the minimal criteria for consciousness in plants. There is already abundant evidence that consciousness in animals depends on the presence of a brain and nervous system. However, many proponents of plant consciousness have argued that plants need not have human-type or animal-type consciousness (Trewavas et al. 2020 ). Instead, they propose that plants have something more “alien” that is nonneural yet still fits the criterion for primary consciousness of raw experience—that is, something it is like to be (Calvo 2017 ).

There is more to the definition of primary consciousness than indicated thus far. First, the raw experience of primary consciousness is divided into two types or aspects (Feinberg and Mallatt 2016a ):

  • Experiencing a mental image or representation of the sensed world.
  • Experiencing affective feelings. Affective essentially means emotional consciousness, which in its simplest form is feelings of good or bad.

Second, primary consciousness is also “understood as the capacities to be aware of the environment and to integrate sensory information for purposeful organismal behavior.” This statement came from a plant-consciousness paper (Trewavas et al. 2020 ) and it is a proper characterization (Feinberg and Mallatt 2018 ), but only if (1) “aware” has its true, dictionary definition as a felt sensory experience and is not misconstrued as mere sensory reception; and (2) “purposeful” means “volitional,” rather than merely “adaptive” in the evolutionary sense of being programmed by natural selection.

Claim 1: each living cell is conscious

Proponents of plant consciousness make two contradictory claims: (1) that consciousness emerged in the first cells before the evolution of plants (Trewavas and Baluska 2011 ; Baluska and Reber 2019 ; Calvo et al. 2020 ), and (2) that it evolved with the first plants (Calvo 2017 ; Trewavas 2017 ). The proponents even made both claims in the same paper (Trewavas et al. 2020 ). So, which is it? This contradiction needs to be explicitly resolved because plant consciousness cannot have any special meaning if it is nothing more than cell consciousness.

Proponents of plant consciousness use a theory called the Cellular Basis of Consciousness or CBC (Reber 2016 ). Here, we enumerate the objections to this theory, new and old (Key 2016 ; Mallatt and Feinberg 2017 ). First, the proponents of CBC seem to equate the fact that cells have sensory receptor molecules (and sensory-response actions) with having conscious sensory perception. They also assume that cellular actions must either be hard-wired (robotic: Reber and Baluška 2020 ) or else conscious, without appreciating the large amount of adaptive plasticity in cell physiology that can produce complex actions without any consciousness. Additionally, they do not realize that the simple forms of learning of which cells are capable—only nonassociative learning (van Duijn 2017 )—do not reflect consciousness, according to behavioral scientists (see Claim 8 below).

Another objection to the idea of cell consciousness is that it traps its proponents in an absurd conclusion about consciousness in humans , the organisms that are most verifiably conscious. After stating that consciousness arose in the first, prokaryotic, cells, Baluska and Reber ( 2019 ) write, “whatever mechanisms [for sentience] operate at the level of prokaryotes will carry on their functions in eukaryotes and multicellular organisms [because] a basic principle of evolutionary biology is that adaptive forms and functions, once established are rarely jettisoned…” Apart from the fact that their “basic principle” is incorrect because evolutionary loss of traits is common (Bleidorn 2007 ; Ellers et al. 2012 ; Futuyma and Kirkpatrick 2017 ), the claim that all cells are conscious necessarily means that all human cells are conscious, never having lost their prokaryote-based consciousness. However, the fact that only brain injuries diminish human consciousness, whereas the loss of our somatic cells does not, is evidence against this idea (also see Ginsburg and Jablonka 2020 , 2021 ).

Arthur Reber addressed the thorny problem of how the separate consciousnesses of our trillions of cells could fit with our single, unified, brain-based consciousness. He proposed that the body’s many cells, through extensive intercellular communication, “turned over” (some of?) their consciousness to the nervous system when the latter evolved, while still retaining their individual cellular consciousnesses (Reber 2019 , pp. 195-196; Reber and Baluška 2020 , p. 3). It is probably untestable, however, and Reber admitted his was a “speculative framework” without supporting evidence.

The idea of cell consciousness also strains credulity with its claim about the origin of plant cellular consciousness. Baluska and his colleagues have proposed that a eukaryotic plant cell is a supracellular unit derived from four ancestral prokaryotic cells (1. cytoplasm and plasma membrane; 2. nucleus; 3. chloroplasts; and 4. mitochondria), whose four consciousnesses became integrated into a single consciousness during evolution (Baluška and Mancuso 2014 ; Baluška and Miller 2018 ; Baluška and Reber 2019 ). Such an extraordinary claim about consciousness requires a substantial amount of hard evidence, but no such evidence was provided.

A major argument used by proponents of cell (and plant) consciousness is that some unicellular organisms can travel over distances in a directed manner, even navigating mazes, to reach a target as if by anticipatory, proactive behavior (Trewavas 2017 ; Baluska and Reber 2019 ). Recently, Tweedy et al. ( 2020 ) delivered a blow to this interpretation. These investigators studied social amoebas and human cancer cells that followed stimulus trails by chemotaxis as the cells detected attractant molecules with receptors on their cell membranes. The migrating cells removed and broke down attractant molecules that had diffused toward them, then they detected and followed the resulting, altered attractant gradient. The key to this was that the cells lowered the concentration of attractant ahead of them . Through this process, the cells readily navigated to the attractant’s source, even following the gradients ahead around corners and through mazes . Therefore, such migratory tracking, which proponents of cell consciousness claim requires intelligent, anticipatory consciousness, is instead fully explainable by a simple mechanism of reception-breakdown-response, with no need to invoke cellular consciousness.

Claim 2: consciousness in plants is indicated because they sense environmental changes and respond adaptively, integrating information for goal-directed behaviors and making decisions along the way

This claim comes from an article by Trewavas et al. ( 2020 ). The term “goal-directed behavior” was defined by evolutionary biologist Ernst Mayr ( 2004 : pp. 51-53) to mean going toward an adaptive endpoint via an evolved, usually genetic, program. By this definition, “goal-directed behavior” applies not only to consciousness but to nonconscious, physiological processes as well. All living organisms perform the adaptive, physiological behaviors of receiving, processing, and responding to stimuli—and we have argued above that not all life is conscious. Therefore, the fact that plants have these behaviors does not make them conscious (Ginsburg and Jablonka 2021 ; Hamilton and McBrayer 2020 ).

Claim 3: membrane potentials and electrical signals are similar in plants and animals, in ways that allow consciousness

Plant cells have membrane potentials and they propagate potential fluctuations that can induce events elsewhere within the plant’s body, either nearby or at a distance (Fromm and Lautner 2007 ; van Bel et al. 2014 ; Gallé et al. 2015 ; Zimmermann et al. 2016 ; Klejchova et al. 2021 ). But how similar are these to the electrical signals carried by animal neurons? Proponents of plant consciousness claim a strong homology:

The working hypothesis of plant neurobiology is that the integration and transmission of information at the plant level involves neuron-like processes (Calvo and Trewavas 2020 : p. 1). Animal-plant similarities being reported in the last decade point toward an electrochemical equivalency at the level of the nervous system elements . . . (Calvo et al. 2017 : p. 2866, after Baluška 2010 ).

The problem with these statements is that there is no “electrochemical equivalency” between animals and plants. Electrical activity in plants is powered by transport of H + and that of animals by transport of Na + (Canales et al. 2018 ). Moreover, the electrical and chemical components of the electrochemical gradient as defined in the Nernst-Planck equation are different: in plants, typically 50–70% of the free energy generated by the plasmalemma H + -ATPases goes into the electrical component (the membrane voltage), the rest into the pH gradient. In animals, it is the other way around: roughly 80–90% of the electrochemical gradient generated by the Na + /K + -ATPases goes into the chemical gradient of Na + (and K + ), and only a small fraction goes into the voltage difference across the membrane (Alberts et al. 2014 ; Klejchova et al. 2021 ).

Proponents of plant consciousness also latch onto the fact that all cells regulate ion fluxes across their plasmalemma to survive and then they conflate this universal property of life with “electrical signaling” to imply consciousness. They ignore the fact that regulated ion fluxes and propagating electrical signals (such as action potentials) exist in many nonneuronal tissues, including those of animals, without any role in processing or integrating information. In short, the presence of electrical activity is not a useful criterion for identifying consciousness in plants.

The following list of signal differences applies to the tracheophyte land plants that are the focus of almost all the literature on “plant consciousness.”

  • i. Plant cells lack the rapidly activating, voltage-dependent Na + channels that give rise to action potentials in animals (Edel et al. 2017 ). Instead, plant action potentials (AP) are normally initiated by Ca 2+ influx (from both external and internal sources), followed by depolarizing Cl − and repolarizing K + fluxes. The resulting all-or-nothing AP is not merely a propagating voltage signal, but also travels together with, and at the same speed as, a concomitant rise in cytosolic Ca 2+ (Chen et al. 2012 ; Minguet-Parramona et al. 2016 ; Klejchova et al. 2021 ). Such propagating calcium elevations also occur in animals for nonneural functions, for example during contraction of the smooth musculature of blood vessels in vertebrates (Borysova et al. 2018 ). Indeed, the Ca 2+ waves in plants have multiple, direct physiological functions that are unlike those of animal neurons. They coordinate local solute fluxes to adjust turgor of plant cells (Minguet-Parramona et al. 2016 ), they signal the presence of pathogenic infections, and they affect mass flow through the vasculature (van Bel et al. 2011 , 2014 ; Klejchova et al. 2021 ). Thus, having action potentials linked to slow calcium elevations gives no indication of neuron-like information processing.
  • ii. Plant action potentials travel more slowly than those of animals, 0.04–0.6 m s −1 versus 0.5–100 m s −1 , respectively, and with long refractory periods between successive action potentials (Fromm and Lautner 2007 ; Canales et al. 2018 ). Only in specialized organs, like the Venus flytrap, are refractory periods shorter, for faster action (Scherzer et al. 2019 ).
  • iii. Plant action potentials cause a net outflow of K + and Cl − ions, whereas animal action potentials are osmotically neutral, suggesting that plant action potentials function in osmotic regulation (Taiz et al. 2019 ; Klejchova et al. 2021 ). The role of action potentials in osmotic adjustment is demonstrably the case in stomatal guard cells (Chen et al. 2012 ; Jezek and Blatt 2017 ). The idea that plant action potentials have their origins in osmoregulation rather than communication is also consistent with the fact that they occur in green algae, the sister group of land plants (Köhler et al. 1983 ; Thiel et al. 1997 ).
  • iv. Electrical-potential fluctuations in plants are highly diverse, based on many different subtypes of ion channels and pumps. These signals also differ according to their location in the plant (root, stem, shoot, etc.), their stage in the life cycle, and their taxonomic group (Zimmermann et al. 2016 ; Canales et al. 2018 : p. 10179; Nguyen et al. 2018 ). This variety is analogous to the diverse actions of membrane- and transepithelial potentials in different organs of animals (Bartos et al. 2015 ; Kadir et al. 2018 ), but not to the specialized, fast potential fluctuations in nervous tissue. The nervous signals are much more uniform, being constrained for optimal speed, energy efficacy, and information transfer.
  • v. Glutamate and its receptors are important for neurotransmission in animals, and glutamate receptors exist in plants. However, their major role in plants appears to be mediating Ca 2+ flux, rather than acting in neurotransmission (Forde and Roberts 2014 ; Nguyen et al. 2018 ; Taiz et al. 2020 ; Klejchova et al. 2021 ).

Finally, it must be stressed that electrical signaling in plants is far less understood than in animals, which should caution researchers against speculating beyond the evidence to assign similarities.

Claim 4: action potentials and other electrical signals for communication propagate, neuron-like, along phloem elements (Calvo et al. 2017 )

The phloem of the vascular system carries electrical signals for considerable distances within plants (Fromm and Lautner 2007 ; Canales et al. 2018 ). Phloem consists of electrically excitable cells called sieve elements , connected to one another in a column ( sieve tube ) at junctions called sieve plates (Fig. ​ (Fig.1). 1 ). However, signal transmission along the phloem differs in notable ways from that on neuronal axons.

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Object name is 709_2020_1579_Fig1_HTML.jpg

Phloem vascular system. a Sieve element. b Sieve tube consisting of seive elements. Reprinted with permission from Taiz et al. ( 2015 ), Sinauer, Oxford University Press

The action potentials carried by phloem differ from animal action potentials, as noted above, by encompassing an osmoregulatory function. Phloem APs also signal distant changes in cellular photosynthesis, respiration, and phloem transport (Fromm and Lautner 2007 ; Fromm et al. 2013 ), but these are arguably caused by a primarily osmotic mechanism: in every case where plant action potentials are documented with mechanistic precision in a physiological response, the central mechanism is osmotic (guard cells and photosynthetic gas exchange, characean algae, carnivorous plants, leaf movements, etc.: Beilby 2007 ; Jezek and Blatt 2017 ; Lawson and Matthews 2020 ).

Phloem-conducted action potentials in plants are commonly responses to noninvasive and nondamaging environmental stimuli, such as touch, cooling, and light (Fromm and Lautner 2007 ; Fromm et al. 2013 ; van Bel et al. 2014 ; Gallé et al. 2015 ). By contrast, the defense responses to destructive wounding and burning injuries are signaled by variation potentials (VPs, sometimes called “slow wave potentials”), which are also conducted by the phloem. Accompanying these VPs are waves of Ca 2+ and reactive oxygen species in the cytoplasm (van Bel et al. 2014 ; Evans and Morris 2017 ; Nguyen et al. 2018 ; Toyota et al. 2018 ; Lew et al. 2020 ; Klejchova et al. 2021 ), with the defense responses including accumulation of jasmonate, salicylic acid, ethylene, and other adaptations to stress.

VPs merit special attention because they are especially relevant to the question of whether plants have the conscious experience of pain. That is, injury-induced VPs are the closest functional analogues in plants to the nociceptive neural signals that lead to conscious pain in animals. Nociception in animals is the nonconscious sensing of injurious stimuli and is not itself pain, but it is processed into pain by higher-level neuronal signaling (Draguhn et al. 2020 ). Therefore, if the electrical properties of plant VPs resemble nociceptive signals, then it is conceivable that plants could also feel pain. Does such a resemblance exist?

No, VPs are different from nociceptive action potentials, and from anything expected to code for consciousness. Plant VPs travel slowly, at only about 0.001 m s −1 (Zimmermann et al. 2009 ; Mousavi et al. 2013 ), far below the 0.5–2 m s −1 of the slow nociceptive action potentials that propagate along human axons after wounding (Purves et al. 2018 ). Unlike action potentials, new VPs can be generated only every 10 min to several hours (Klejchova et al. 2021 ) and they decay over time and distance (decreasing in amplitude). Each VP is unitary and long-lasting (for over 5 min: Nguyen et al. 2018 ). VPs cannot signal all the way from one end of a plant to another, either by amplitude or velocity. Another characteristic that precludes neuron-like encoding by VPs is that they are highly variable in amplitude and temporal behavior, unlike the frequency encoding that characterizes electrical spike trains in neurons and is necessary for consciousness in animals (Dennett 2015 ; Klejchova et al. 2021 ).

In summary, phloem transmits APs and VPs, neither of which is similar to signal transmission in neural axons. The VPs seem especially unsuitable for any role in consciousness.

Claim 5: plants, like animals with neurons, use electrical signals to integrate information for consciousness

Information integration has a detailed, formal definition (Tononi and Koch 2015 ; Koch 2019 ) that roughly means the parts of a system interact so the outputs differ from the mere sum of the inputs. For plant neurobiology, however, Calvo ( 2017 : p. 212) treats information integration as combining and processing diverse information to make decisions about responses. That is the sense in which we use the term here.

The consensus of opinion among those who study consciousness in animals is that it depends on information integration that involves extensive feedback, or reciprocal (recurrent) communication, between the conductive neurons (Lamme 2006 ; Feinberg and Mallatt 2018 ; Koch 2019 ; Mashour et al. 2020 ). This reciprocal connectivity is shown in a human brain in Fig. ​ Fig.2. 2 . Such integrative electrical signaling is easily recorded among neurons in the brains of conscious humans as well as in brains of other mammals performing the same mental tasks (Fahrenfort et al. 2007 ; Storm et al. 2017 ), but it has never been detected in plant phloem or any other part of a plant. That is, forward signals are documented but feedback signals have not been found. Such integrating signals have merely been hypothesized to occur (Calvo et al. 2017 : p. 2866; Taiz et al. 2020 ). In legumes, a type of reciprocal signaling occurs between shoots and roots to regulate the formation of root nodules that contain N 2 -fixing bacteria, but this is different: only the first, local signaling steps are electrical whereas most of the steps are nonelectrical and involve long-distance movements of peptides via the vascular system (Krusell et al. 2002 ; Damiani et al. 2016 ; Roy et al. 2020 ).

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Extensive reciprocal communication (back-and-forth arrows) between processing centers (ovals) in the human brain is an indicator of consciousness. Such integrative communication also occurs within the centers (not shown). This is a side view of the brain, with anterior to the right. For simplicity, we only label/number a few of the main centers: 1. primary visual cortex of the cerebrum; 2. somatosensory cortex; 3. amygdala (for fear and other emotions); 4. thalamus; 5. superior colliculus of midbrain (optic tectum). Modified from Fig. 3 in Feinberg and Mallatt ( 2020 )

For the information integration of consciousness, another generally accepted requirement is a high degree of interconnectivity among neurons. An average neuron in the human brain contacts about 10,000 other neurons (Zhang 2019 ), through its many branching processes and synapses. In contrast, the phloem vascular bundles in the internodes of plants are primarily unbranched and linear, and both sugar translocation and signaling occur along this linear axis. However, branches with anastomoses (interconnections) can occur between adjacent bundles to form a network for the lateral movement of water, minerals, and photosynthetic products (Fig. ​ (Fig.3). 3 ). However, these anastomoses are not more elaborate than in blood-vessel networks of animals (Kopylova et al. 2017 ; Alves et al. 2018 ), which are not involved with consciousness. Even so, they led Calvo et al. ( 2017 ) to suggest that phloem networks have the additional function of generating consciousness in plants, by analogy to the neuronal networks in animal brains.

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Longitudinal view of the phloem in Dahlia pinnata . Patterns of phloem anastomoses (arrows) are evident between the longitudinal vascular bundles. The phloem was removed from the xylem at the cambial zone, and is shown from the cambium side in an intact stem, stained with aniline blue and observed under epifluorescence microscope. Scale bar = 100 μm. Micrograph is a gift from Roni Aloni

A difficulty with this argument is that phloem anatomoses are absent in young internodes (Aloni and Barnett 1996 ). If phloem anatomoses are required for plant consciousness, the growing tip and younger internodes of a plant would be nonconscious, even though these are essential for regulating tropistic curvatures in growing plants and nutational movements—actions that are often cited as outward expressions of plant consciousness (Gagliano et al. 2016 ; Calvo 2017 : p. 219; Calvo and Trewavas 2020 ). Phloem anastomoses are also absent in young germinating seedlings, yet seedlings still exhibit many of the behaviors of mature plants. If the function of plant consciousness is to allow plants to make important “decisions,” why would it be active in mature plants but not in young seedlings, the most vulnerable part of the life cycle?

For other arguments against phloem anastomoses resembling neuronal networks, see Taiz et al. ( 2020 ).

Claim 6: plants have a brain (“command center”) in the root

From early comments by Charles Darwin ( 1880 ) on the ability of the root tip to control the direction in which a root grows, Baluska and colleagues consider this tip a “brain-like command center” (Baluška et al. 2004 , 2009 ; and the “somatic mosaic” idea in Calvo et al. 2020 ). Baluška and Hlavačka ( 2005 ) and Baluška et al. ( 2009 ) cite actin-rich domains in these root cells as evidence of endocytosis and vesicle recycling reminiscent of neuronal synapses. However, there is no clear cytological evidence for synapses in plants (Hertel 2018 ; Robinson et al. 2018 ; Taiz et al. 2019 , 2020 ).

Moreover, the transition zone of the root tip (Fig. ​ (Fig.4), 4 ), between the apical meristem and the zone of elongation, is a peculiar place to situate a putative brain-like organ for consciousness and memory storage. In the first place, the dividing cells of this transition zone are immature and undifferentiated (Salvi et al. 2020 ), unlike functioning neurons, which are mature and fully differentiated. By analogy, the dividing, undifferentiated pre-neurons in the embryonic vertebrate brain have not yet developed their cell processes or formed functioning networks required to generate consciousness (Sadler 2018 ).

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Histomicrograph of a root tip, from flax ( Linum usitatissimum ). The zone of elongation lies just above the top of the micrograph. Reprinted with permission from Taiz et al. ( 2015 ), Sinauer, Oxford University Press

A second objection to the “transition zone equals brain” proposal arises from the indeterminate growth of plants. Due to the growth activity of the apical meristem, the cells that form the primary plant body are progressively displaced away from their point of origin at the growing tip toward the mature base of the root or stem. Primary growth at the cell level can be analyzed by kinematic methods that describe the movements of points or bodies through space (Erickson and Silk 1980 ). By measuring the relative elemental growth rates of cells in different zones, one can determine the turnover rates of cells at specific locations in the tip (Silk and Erickson 1979 ; Silk et al. 1986 ). In the maize root, for example, the entire population of cells in the transition zone is displaced into the zone of elongation roughly every 4.7 h (Wendy Silk, personal communication). The turnover rate would, of course, vary depending on the species and growth conditions, but the problem remains that the cells in this developmental zone are constantly being displaced. The continuous displacement of cells out of the “brain-like command center” is incompatible with the formation of the stable processing networks capable of generating consciousness, feelings, and volition . Nor is consciousness even necessary, because growing root tips process environmental stimuli by ordinary molecular signaling within and between their cells, by releasing hormones, Ca 2+ , and other known molecules to effect a response (Chaiwanon and Wang 2015 ; Taiz et al. 2015 ; Kong et al. 2018 ).

To be fair, it is important to point out that only some proponents of plant consciousness make the claim for a brain-like command center. Others, by contrast, accept its absence but argue that this absence does not preclude consciousness (Calvo 2017 ; Trewavas 2017 ). By analogy to the social insects, they advocate a distributed or “swarm intelligence,” stating that consciousness arises collectively from interactions between many tissues throughout the plant body. However, we question whether swarm intelligence has any relation to individual consciousness—and, there is considerable doubt whether “collective consciousness” even exists as an entity (Feinberg and Mallatt 2016a : p. 197; Friedman and Søvik 2019 ; Ginsburg and Jablonka 2021 ).

Claim 7: plants show proactive, anticipatory behavior

Proponents claim that plants exhibit proactive behaviors, not just reactive ones, and that this intentional, proactive behavior indicates consciousness (Calvo 2017 ; Calvo and Friston 2017 ; Trewavas 2017 ; Latzel and Münzbergová 2018 ). Most of their examples involve the growth of roots, shoots, or climbing vines toward a goal or away from harm (e.g., Shemesh et al. 2010 ). But these examples always involve sensing and following a stimulus trail (“responses to stimuli”; “proactively sampling”: Calvo et al. 2017 ; Calvo and Friston 2017 ), which is reactive, not proactive. Rather than reflecting consciousness, it seems that plant growth patterns are preprogrammed to follow environmental clues. Truly proactive behavior that indicates consciousness would be to find the goal in the absence of a sensory trail , based on a mental map of the surrounding environment (Klein and Barron 2016 ; Feinberg and Mallatt 2018 : p. 58) and on memories of this mapped space (Feinberg and Mallatt 2016a : pp. 114-115).

An example of true, planned, proactive behavior comes from experiments on spartaeine spiders (Tarsitano and Jackson 1997 ; also see Cross and Jackson 2016 and Perry and Chittka 2019 ). In the experiment, each spider started at the top of a tall cylinder where it could view two above-ground perches below it, on one of which was a prey. To get to the prey, the spider had to climb down from its cylinder onto the ground, from which the prey was no longer visible, and then choose between two paths made of bent poles, one of which led to the perch with the prey and the other to the perch without the prey. The spider walked along these poles, whose bends assured the spider had to go back and forth in “detours” and reach the perches indirectly—and the prey remained invisible until the spider climbed onto the perch. Even though they had never experienced the apparatus before, the spiders chose the correct route to the prey significantly more frequently (usually 2 to 4 times more) than they chose the wrong route. A key point is that there was no sensory trail to follow: the spider saw the prey only at the start, and the prey was imbedded in clear plastic so there was no olfactory cue to track. This means the spiders scanned and planned their routes in advance and formed some sort of mental representation of where to go. This is what we mean by proactive, conscious behavior. Plants have not been shown to meet the criteria for this behavior, because to date the experiments with plants have not removed access to the stimulus trail.

Instead plant movements resemble those of the roundworm Caenorhabditis elegans ( C. elegans ), which is the representative non conscious animal (Barron and Klein 2016 : Klein and Barron 2016 ). When foraging in soil for its bacterial food, this worm continually uses many senses (taste, smell, touch, moisture) to track and find the richest bacterial patches (Ardiel and Rankin 2010 ; also see Gang and Hallem 2016 ), and it usually succeeds, especially when, upon losing the trail, it conducts a thorough and patterned search.

The preprogrammed searching of C. elegans , as a characteristic nonconscious behavior, resembles the winding growth movements of plants (circumnutation) that help them to find targets. It is therefore wrong to claim (Calvo 2017 ) that of these two organisms, only C. elegans lacks “goal-directed behavior” (incorrect because foraging is goal-directed by definition, the goal being to find the food or other resource). It is also erroneous to claim that “anything beyond their immediate surroundings eludes C. elegans ,” because C. elegans follows the sensory trail out of its immediate surroundings and eventually finds distant food. And to claim that C. elegans “is unable to go beyond the here and now” is also incorrect because this worm persists in following the sensory trail for as long as it takes to achieve the goal. These observations show that certain nonconscious organisms can do impressive things without any proactive behavior. Another splendid example is the efficient foraging by fungal mycelial networks in the forest floor (Fricker et al. 2017 ), fungi also being nonconscious by our criteria. And recall how impressive but nonconscious foraging can be aided by attractant breakdown (Claim 1 above: Tweedy et al. 2020 ).

Claim 8: plants show classical associative learning, which indicates consciousness

To start with some background information, ethologists divide associative learning into two types. The first type is classical or Pavlovian learning (the simpler type). This is learning to associate a new stimulus with one that already causes an established behavior. An example is Pavlov’s dogs (Fig. ​ (Fig.5). 5 ). The second type is operant or instrumental learning (the more advanced type), which is learning from experience to change a behavior. For example, when a lab rat in a box accidentally pulls a lever, obtains a food reward, and learns to press the lever after a few trials, it exhibits operant learning.

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Classical associative learning, step by step. Here, a dog learns from a ringing bell (conditioned stimulus) that is presented prior to the smell of food (unconditioned stimulus) to salivate in response to the bell sound alone. Above, the pretraining steps show that the food alone induces drooling ( a ) but the bell alone does not ( b ). Training ( c ) rings the bell before presenting the food. After training ( d ), the bell alone induces drooling

Adelman ( 2018 ) recently reviewed the literature on whether plants have associative learning, with most of the studies having been done in the 1960s. His findings were a mixture of negative and positive results, but that none of the positive results had been replicated. Gagliano et al. ( 2016 ) claimed to have shown Pavlovian learning in growing pea seedlings, but Markel ( 2020a , b ) could not replicate this, indicating problems with the controls in the original study.

A second study also reported associative learning in plants (Latzel and Münzbergová 2018 : their Fig 3). In the main part of this study, rooting ramets of the clonal wild-strawberry Fragaria vesca were “trained” to grow onto nutrient-rich patches of soil either in the light (attractive) or the shade (less attractive), and then were monitored to see if they preferentially grew into lighted or shaded patches in the absence of nutrients. The results were a spotty mix of positives and negatives: plants that had been trained on lighted patches sent a significantly greater biomass of ramets to the lighted patches ( p < 0.05) as predicted, but not a greater number of ramets; and then the opposite relationship between number and biomass inexplicably occurred for ramets that had been trained in the shade (except that the p values here were not quite significant—between 0.05 and 0.1). And another, “epigenetic,” part of the study used a chemical spray to demethylate the Fragaria plants’ genomes with the intent of erasing any ability to learn. There, however, the single statistically significant effect was “exactly the opposite” of that predicted. Yet all these negative and inexplicably opposite findings, both in the main study and the epigenetic experiment, were never addressed. Instead, the authors treated the results as though they were positive and significant.

We conclude that classical learning in plants remains unproven. But with regard to plant consciousness, it does not matter either way because classical learning has always been considered nonconscious (Goldman 2012 ; Rolls 2014 ; Rehman et al. 2020 ). Classical learning in the sense of behavioral adaptation to associations between two cues is fully explainable by changes of synaptic connectivity. This can occur without any complex perceptual or motor integration; e.g., at the simple level of reflex pathways like the gill-withdrawal reflex of the sea hare, Aplysia californica (Kandel and Schwartz 1982 ; Kandel 2009 ).

The clearest demonstration that classical learning is not conscious is that the isolated spinal cord of a human or rat can learn classically (note: we adopt the dominant view that the spinal cord is not conscious: Koch 2018 ). The relevant experiment is shown in Fig. ​ Fig.6 6 (Joynes and Grau 1996 ). Here, a rat’s spinal cord learns to associate a mild shock to the leg with an antinociceptive shock to the tail so the tail becomes less responsive to nociceptive heating. The interpretation is that, through classical learning, the leg shock has taken on a new, antinociceptive role .

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Classical learning by a spinal cord. Drawing is modified from Huie et al. ( 2015 ). The spinal cord was transected in the upper thorax 1 day before the learning experiment, so it was isolated from the brain. CS means conditioned stimulus (leg shock) and US means unconditioned stimulus (tail shock). During training, the mild shock to the leg is given just before an antinociceptive shock to the tail, the latter being a shock that naturally diminishes tail flick in response to the focused heat. With learning, the leg shock diminishes this tail flick when given alone (that is, it increases the latency time), having become antinociceptive

An isolated, nonconscious spinal cord can even learn operantly . The relevant experiment (Grau et al. 2006 ) trained a rat’s leg to lift up for a longer time, to avoid a punishing shock (Fig. ​ (Fig.7). 7 ). This is true operant learning, but it is limited to a single kind of response and has no learning flexibility. Still, even limited operant learning is beyond anything ever found in plants. Neither it nor classical learning, if at all present in plants, would mean they are conscious.

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Limited operant learning by an isolated spinal cord. In the picture, the rod electrode also acts as a plate for the rat’s foot. A shock from the shocking electrode causes the leg to lift up, after which the leg naturally drifts down so the rod electrode enters the salt solution, completing a circuit that delivers another shock. As the cycle keeps repeating, the time it takes for the leg to drift down increases as the cord learns to delay the next punishing shock. Picture modified from Grau et al. ( 1998 )

Claim 9: plants communicate with each other in a purposeful manner and, hence, have conscious self-recognition

The exchange of volatile organic chemicals or other signals between plants has been interpreted as an adaptive behavior resembling cognition (Karban 2008 ; Leopold 2014 ; Trewavas 2016 ). Moreover, signaling between plants was taken as evidence that they distinguish between self and alien; i.e., for self-recognition (Trewavas 2017 ). Collective behavior of plant communities has, consequently, been interpreted as cooperative behavior indicating social cognition, intelligence, and thought (Karban 2008 ; Baluška and Manusco 2020 ). None of these observations requires consciousness, cognition, or collective planning. Exchange of signals between organisms is a widespread phenomenon in biology, beginning at the level of collective behavior in bacterial biofilms (Prindle et al. 2015 ). The communication occurs because all organisms evolve to detect (via receptors) every relevant and beneficial external stimulus, including molecules emitted by other organisms. And because all living organisms are defined by borders, they have an elementary distinction between self and alien. This distinction can be complex and adaptive, as, for example, in immune systems (Abbas et al. 2019 ). It does not, however, reflect or constitute consciousness.

Given these considerations, proponents can only argue that plant communication indicates consciousness if every living organism is conscious, including every bacterium—a highly problematic argument, as pointed out in Claim 1 above.

Claim 10: detailed hypotheses, predictions, and models can substitute for hard evidence of plant consciousness

The proponents of plant consciousness in effect make this claim about the value of reasoned speculation. They do so by piling theory upon theory far beyond the evidence, as exemplified by this quote from Calvo et al. ( 2017 : p. 2866). We italicized and underlined the many words and phrases that indicate uncertainty and speculation.

We have used some very old and modern literature to indicate unanswered questions about electrical signaling. The reticulated excitable phloem system described above offers a potential for assessment of signals and perhaps their prioritization. The bioelectric field in seedlings and in polar tissues may also act as a primary source of learning and memory. But we suspect that with time and experience, the developing phloem becomes increasingly cross-linked and memory could then reside in the electrical capabilities determined by numbers and characteristics of the cross linking. Local phenotypic changes to accommodate local environmental situations are characteristic of the behaviour of the self-organizing plant, and maybe , the bioelectric field coordinates with the electrical system to provide for the characteristics of self-organization. Both local and long distance changes are characteristics of higher plants. The vascular network is a complex interactive system, and once stimulated, it has the potential for assessment through possible feedback and alterations of connection strength. Animal-plant similarities being reported in the last decade point toward an electrochemical equivalency at the level of the nervous system elements (Baluška 2010 ), integrated by spatiotemporal dynamics (Masi et al. 2009 ). Whether it should be regarded as a functional equivalent to a fairly primitive brain cannot be determined until its properties are more clearly defined by research . This article commenced by pointing out that lack of obvious movement in plants has led to incorrrect suppositions about a nervous control. With recognition that this highly branched excitable plant nervous system might act holistically, some issues that have dogged this area of research might be better understood.

On first consideration, it seems unfair to criticize such extreme speculation, because the authors explicitly stated that the goal of their article was “to indicate unanswered questions” about the topic of sentience. However, these are not one-time questions but ideas they believe to be true and continually promote in their publications without evidence (Baluška et al. 2009 ; Calvo 2017 ; Calvo and Trewavas 2020 ; Trewavas et al. 2020 ). Multiple speculative leaps without hard evidence are not only bound to introduce fatal errors in the chain of argument, but they also make the endeavor overly complex.

So far, we have examined ten claims for plant consciousness and none has held up.

The alternate hypothesis of Feinberg and Mallatt

In order to analyze the final two claims for plant consciousness, we must first present a hypothesis by which to judge these claims. This hypothesis, called neurobiological naturalism, was developed by Todd E. Feinberg and one of us (JM) (Feinberg 2012 ; Feinberg and Mallatt 2013 , 2016a , b , 2018 , 2019 , 2020 ). One of its goals was to identify which organisms have consciousness. To this end, we started with just two, logical assumptions.

Assumption 1: affective (emotional) consciousness

From what assumption did we deduce which organisms have emotional consciousness? We assumed that emotions could be revealed by the capacity for operant learning from experience, because such reward- and punishment-induced learning goes with positive and negative emotions in humans. But we knew that simple operant learning can be non conscious (Fig. ​ (Fig.7), 7 ), so the criterion we chose is high-capacity operant learning: learning a brand-new behavior that uses one’s whole body (Feinberg and Mallatt 2016a : pp. 152-154). For example, a rat reveals emotional attraction when it has learned to walk to a lever and press the lever for a food reward. We adopted this assumption because it is double evidence of emotional feelings. That is, the existence of emotion is suggested by both (1) the initial attraction to a reward, and (2) recalling the learned reward to motivate behavior.

The only organisms that fit this criterion for affective consciousness are the vertebrates (all), arthropods (all), and cephalopods (octopus, squid, cuttlefish). Also see the similar theory of Bronfman et al. ( 2016 ) and Ginsburg and Jablonka ( 2019 , 2021 ), with which we agree. Now we are ready to evaluate the claim that plants have affective consciousness.

Claim 11: plants show affective (emotional) consciousness

Gagliano ( 2017 ) advocated affective consciousness in plants, by saying that their classical associative learning indicates “internal value systems based on feelings.” Her term “value systems” confirms that she was talking about the emotional feelings of affective consciousness, because “internal value” refers to valence , meaning the affective qualities of good = attractiveness and bad = averseness (Frijda 1986 ). We already refuted Gagliano’s claims for affects in plants, by showing that classical learning is nonconscious (see Claim 8 above).

Next we turn to the other type of primary consciousness, the image-based type.

Assumption 2: image-based consciousness

For this type, we assumed that any organisms that demonstrably encode maps of the surrounding environment and of their bodies—from multiple senses such as vision, smell, touch, and hearing—will experience these mapped simulations consciously (Feinberg and Mallatt 2013 , 2016a ). It seems reasonable to assume that if a brain or body expends the energy to assemble such detailed maps, then it will use them, say, as mental reference images for moving and operating in the world.

Figure ​ Figure8 8 shows such mapped neuronal representations in humans up to the higher brain (cerebral cortex). Each of these pathways is known and has been documented (Brodal 2016 ). Other investigators have also related this kind of mapped representation to consciousness (Edelman 1989 ; Kaas 1997 ; Damasio 2010 ).

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Neuronal sensory maps in the human nervous system. For each sense, a path of several neurons (far right) is a hierarchy that carries signals up to the brain, keeping a point-by-point mapping (A, B, or C) of the outside environment or a body structure. On reaching the cerebral cortex, this leads to the mapped neural representations that are shown around the brain. Information from the different senses is combined for multisensory integration (Stein et al. 2020 ), especially in the posterior cortical hot zone (Koch 2019 : p. 61). Here, this seems to lead to a unified, all-sense map of the world that characterizes consciousness. This illustration is from Feinberg and Mallatt ( 2018 ). Used with permission from © Mount Sinai Health System

This sensory mapping is only documented to exist in the nervous systems of certain animals, namely in all the vertebrates and arthropods, and in cephalopod molluscs (Feinberg and Mallatt 2016a ). Therefore, these are the clades with image-based consciousness, and they are the same clades we found above to have affective consciousness (Fig. ​ (Fig.9). 9 ). They are also the animals with the most complex brains. Now we are ready to evaluate the claim that plants have image-based consciousness.

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Summary figure showing that the conscious organisms, all of which we deduced to have both affective and image-based consciousness, do not include plants. The vertebrates are Komodo dragon Varanus and bowfin fish Amia . The arthropods are crustacean Nebalia and ladybug beetle Coccinella . The cephalopods are a cuttlefish and an octopus

Claim 12: plants have image-based consciousness, based on internal representations

A paper that was coauthored by the main proponents of plant consciousness claimed that within a bacterium “the environment is internally mapped” and that this likely holds for plants as well (Calvo et al. 2020 ). That paper also suggested that groups of cells within a plant’s body combine to construct an image, through “somatic mosaics.” But no evidence was presented for any of this. And the proponents effectively admit that too little is known about electrical signaling in the phloem vasculature to tell if phloem carries any mapped sensory information: see the quote from Calvo et al. ( 2017 ) in Claim 10 above.

The evolution of consciousness

We have found that two separate lines of reasoning—one about affective consciousness and the other about image-based consciousness—agree that vertebrates, arthropods, and cephalopods are the only conscious organisms and that plants are not included. Consciousness must have appeared independently by convergent evolution in each of the three animal lines, because reconstructing their history indicates their last common ancestor lacked a brain (Northcutt 2012 ).

Note that the assumptions from which we deduced which organisms are conscious—the assumption of mapped representations for image-based consciousness, and of high-capacity operant learning for affective consciousness—have little to do per se with locomotor ability or fast mobility, yet they identified the most mobile clades of animals as the conscious ones (Fig. ​ (Fig.9). 9 ). Thus, our reasoning has independently reinforced the standard view that consciousness can only evolve in highly mobile organisms (Merker 2005 ; Taiz et al. 2019 ).

Conclusions

This paper presents new arguments against plant consciousness, the most important of which are:

  • A. Plants do not show proactive behavior.
  • B. Classical learning does not indicate consciousness, so reports of such learning in plants are irrelevant.
  • C. The considerable differences between the electrical signals in plants and the animal nervous system speak against a functional equivalence. Unlike in animals, the action potentials of plants have many physiological roles that involve Ca 2+ signaling and osmotic control; and plants’ variable potentials have properties that preclude any conscious perception of wounding as pain.
  • D. In plants, no evidence exists of reciprocal (recurrent) electrical signaling for integrating information, which is a prerequisite for consciousness.
  • E. Most proponents of plant consciousness also say that all cells are conscious, a speculative theory plagued with counterevidence.

Our 12 counterarguments are important to the future of plant biology, because dubious ideas about plant consciousness can harm this scientific discipline. We foresee three types of harm. First, not only does the notion of plant consciousness mislead the general public, but it also can generate mistaken ideas about the plant sciences in young, aspiring plant biologists . Second, the strong, romantic appeal of plant consciousness could influence public and private funding agencies to fund projects that are based on its fallacies. Third, public acceptance of plant consciousness could affect research regulation . For instance, could research on genetically modified plants face even more resistance if plants were regarded as conscious? How might laboratory-research regulations be impacted when scientists are seen to perform invasive manipulations on plants that feel pain?

These are not idle concerns. Articles that promote plant neurobiology thinking are increasingly finding their way into respectable scientific journals—even top-tier journals (Calvo and Friston 2017 ; Tang and Marshall 2018 ; Baluška and Manusco 2020 ; Calvo et al. 2020 ). This is most regrettable, and hopefully our article, by putting the record straight, will reverse this trend. In conclusion, we feel we must speak forcefully: plant neurobiologists have become serial speculationists. The ratio of speculation to data in their oeuvre is astronomically high. If they want to form a sensible hypothesis and then test it with real experiments, that is fine, but the prolific speculating and fantasizing need to stop.

Acknowledgments

Thanks to Roni Aloni, Rainer Hedrich, Kasey Markel, Gerhard Thiel, and Daniel Alkon, who answered our questions and/or kindly read and commented on this paper. Jill K. Gregory contributed to the art in Figs. ​ Figs.2 2 and ​ and8 8 .

Authors’ contributions

J.M., L.T., and D.G.R. contributed to the study’s conception and design. J.M. contributed most to the consciousness and learning aspects, and M.B. to the plant electrophysiology. L.T. provided much on the concept that not all adaptations are conscious, on root tips, and phloem anastomoses. A.D. contributed to the electrophysiology and wrote the section on plant communication. D.G.R. commented on everything and made sure we moved things along smoothly. J.M. wrote the drafts, and all authors provided input to all drafts. All authors read and approved the final manuscript.

Data availability

Compliance with ethical standards.

The authors declare that they have no conflict of interest.

All authors consent.

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Contributor Information

Jon Mallatt, Email: ude.ohadiu@ttallamj .

Michael R. Blatt, Email: [email protected] .

Andreas Draguhn, Email: [email protected] .

David G. Robinson, Email: [email protected] .

Lincoln Taiz, Email: ude.cscu@ziatl .

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Anesthetics and plants: no pain, no brain, and therefore no consciousness

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  • Published: 02 September 2020
  • Volume 258 , pages 239–248, ( 2021 )

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research on plants feeling pain

  • Andreas Draguhn 1 ,
  • Jon M. Mallatt 2 &
  • David G. Robinson   ORCID: orcid.org/0000-0002-0394-490X 3  

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Plants have a rich variety of interactions with their environment, including adaptive responses mediated by electrical signaling. This has prompted claims that information processing in plants is similar to that in animals and, hence, that plants are conscious, intelligent organisms. In several recent reports, the facts that general anesthetics cause plants to lose their sensory responses and behaviors have been taken as support for such beliefs. These lipophilic substances, however, alter multiple molecular, cellular, and systemic functions in almost every organism. In humans and other animals with complex brains, they eliminate the experience of pain and disrupt consciousness. The question therefore arises: do plants feel pain and have consciousness? In this review, we discuss what can be learned from the effects of anesthetics in plants. For this, we describe the mechanisms and structural prerequisites for pain sensations in animals and show that plants lack the neural anatomy and all behaviors that would indicate pain. By explaining the ubiquitous and diverse effects of anesthetics, we discuss whether these substances provide any empirical or logical evidence for “plant consciousness” and whether it makes sense to study the effects of anesthetics on plants for this purpose. In both cases, the answer is a resounding no.

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Introduction

research on plants feeling pain

Anaesthetics and plants: from sensory systems to cognition-based adaptive behaviour

research on plants feeling pain

Debunking a myth: plant consciousness

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With the aim of eliminating pain, memory, movements, and conscious experience during operations, volatile anesthetics were introduced into medical practice more than 170 years ago. Interestingly plants also react to these substances as originally demonstrated by Claude Bernard in 1878, causing him to claim that “… plants and animals must share common biological essence that must be disrupted by anesthetics” (Bernard 1878 ; Grémiaux et al. 2014 ). In the following 100 years, reversible inhibitory effects of anesthetics on various aspects of plant growth and motility were recorded (e.g., Bancroft and Rutzler 1931 ; Bünning 1934 ; Taylorson 1982 ), with little indication as to their mode of action. With the introduction of the plant neurobiology concept (Brenner et al. 2006 ), the notion that plants are conscious organisms has become more popular, especially in the popular press (e.g., Trewavas and Baluska 2011 ; Calvo et al. 2017 ; Gagliano et al. 2017 ; Trewavas 2017 ; Mancuso 2018 ). Consciousness is defined as the capacity of an organism to have experiences, to feel sensations, and to carry out voluntary behaviors (Nagel 1974 ; Mallatt et al. 2020 ). Because anesthetics induce an unconscious state in humans, their effects on plants have been taken to indicate the existence of consciousness in plants, including the conscious perception of pain (Baluška 2016 ). This apparent similarity has prompted plant neurobiologists to analyze anesthetic’s effects more closely (Yokawa et al. 2018 , 2019 ; Pavlovič et al. 2020 ). Among the reversible effects they recorded are the loss of responsiveness to external stimuli, cessation of phototactic and plant organ movements, inhibition of seed germination and of accumulation of chlorophyll, alteration of ROS homeostasis, impairment of jasmonate signaling, blockage of action potentials, and inhibition of endocytic vesicle recycling. The impairment of jasmonate signaling has received special attention recently (Pavlovič et al. 2020 ) because jasmonate is involved in long-distance electrical communication in plants. Therefore, its disruption has been taken as evidence for systemic effects of anesthetics similar to the disruption of coordinated information processing in the mammalian brain (Trewavas et al. 2020 ). Together, the effects of anesthetics on local and systemic functions of plants have evolved into a major argument for similarities between plants and animals with respect to consciousness. Due to these proclaimed similarities, plants are being advertised as model organisms for studying anesthetics (Yokawa et al. 2018 , 2019 ; Baluška and Reber 2019 ).

Volatile general anesthetics include diethyl ether, isoflurane, sevoflurane, halothane, and more. Each affects a large variety of molecular targets, many of them being present—in homologous or analogous forms—in all living phyla (Kelz and Mashour 2019 ). The best studied of these general effects, demonstrated in organisms ranging from bacteria to plants to animals, is altering the functions of many kinds of protein receptors and ion channels in cell membranes (Hemmings et al. 2019 ). In animals, anesthetics especially affect neurons , leading to specific effects in their nervous systems (which plants lack). As an overall neural effect, anesthetics disrupt coordinated activity patterns within and between neuronal networks, suppressing sensation, action, and conscious experience (Kelz and Mashour 2019 ; Akeju and Brown 2017 ). The underlying mechanisms are not fully understood but the effects on ion channels seem to be a large part, and all known molecular and cellular effects converge on a disruption of synaptic transmission and electrical activity in neuronal networks. These effects are most likely mediated by the potentiation of inhibitory and the suppression of excitatory postsynaptic transmitter receptors, a general reduction of neurotransmitter release, and reduced intrinsic neuronal excitability. Further actions on the cytoskeleton and mitochondrial complex I are believed to add to the impairment of synaptic transmission (Kelz and Mashour 2019 ). As a result, network- and system-level activity of the brain is altered to end consciousness, in a way that shows some similarities, but also profound differences to sleep (Akeju and Brown 2017 ). Depending on their chemical structures and concentrations, different anesthetics affect different neural subsystems, leading to specific effects and prompting differential clinical uses.

We thus have to distinguish the general effects of anesthetics, which likely apply to all living matter, from the specific effects on neuronal mechanisms in the brain of humans and animals. The latter explain the specific and reversible disruption of perception and consciousness, which occur in animals that possess the required brain structures. One of the most distinct actions of anesthetics in mammals is, of course, mitigating or abolishing the sensation of pain (Rowley et al. 2017 ). This is not only a primary reason for their clinical use, it is also closely linked to consciousness (Feinberg and Mallatt 2016 ; Walters and Williams 2019 ). Therefore, pain provides a handle to study consciousness in nonverbal organisms.

Those who advocate the effects of anesthetics on plants as proof for their consciousness (Baluška et al. 2016 ; Yokawa and Baluška 2018 ; Yokawa et al. 2018 ; Pavlovič et al. 2020 ; Trewavas et al. 2020 ) challenge prevailing concepts of the neuronal basis of this complex state. Pain-relieving effects of such substances in animals and humans have been used to infer subjective pain experiences in plants (p. 6 in Baluška et al. 2016 ). This argument raises severe semantic, conceptual, and scientific problems. We will therefore summarize current knowledge on pain in humans and animals and critically ask whether the effects of anesthetics in plants suggest they also feel pain. We will then extend our arguments to the question of consciousness and ask whether anesthetics provide any evidence for its existence in plants. As a whole, we hope to show the irrelevance of studying anesthetics in plants for promoting concepts such as plant sentience, plant cognition, or plant consciousness.

Pain in humans: a complex experience and its neural basis

As defined by the International Association for the Study of Pain ( https://www.iasp-pain.org/terminology?navItemNumber=576#Pain ), pain is “an unpleasant sensory and emotional experience associated with actual or potential tissue damage.” Thus, as originally described by the eminent British neurophysiologist and Nobel Prize winner, Charles Scott Sherrington, pain is a subjective experience following on from a physiological process involving neuronal stimulation by cues indicating tissue damage. This peripheral physiological process, termed “nociception” (from the Latin verb nocere , which means to harm), is not identical to pain. It only triggers electrical activity in nociceptive neural pathways and widespread networks of the brain that then give rise to the perception of a lesion, adequate reactions, and the subjective experience of pain. Pain is a particularly salient and emotional experience that almost inevitably demands our full attention. This is why it has a central role in the study of consciousness (Feinberg and Mallatt 2016 ; Harnad 2016 ; Walters and Williams 2019 ).

In mammals, the detection of harmful chemical, mechanical, or thermal cues (collectively termed noxious stimuli) is accomplished by nerve endings (nociceptors) found in the skin, joints, and multiple other organs. Nociceptors express a large variety of membrane-bound receptor molecules for the different types of potentially damaging stimuli (e.g., cuts, extremes of pH, and temperature). The nociceptors come in diverse forms—some triggering the sharp, well-localized sensation of pain immediately following a pinprick; others the delayed, nasty sensation of a burning pain seconds after we hurt ourselves; and others the sensation of itch. They also carry receptors for inflammation molecules that enhance their reactivity, as we all know from the hypersensitivity at or around an infected fingernail or any other local irritation. With this molecular toolkit, nociceptors “translate” damaging stimuli into electrical signals. These signals, called action potentials, are fast fluctuations of the membrane potential travelling along the nerve fiber of the nociceptor neuron, reaching the spinal cord and then transferring the excitation to secondary neurons in the central nervous system. From there, activity is distributed within a large, widespread network of different brain regions. It is the combined activation pattern of these brain regions, called “pain network” or “pain matrix,” that does finally give rise to the complex, unpleasant sensation of pain.

Looking into the locations and functions of the different brain areas for pain processing is instructive to understand further physiological and psychological features of pain (Craig 2003 ; Almeida et al. 2004 ). Nerve fibers from the spinal cord send branches to many different parts of the brain stem and forebrain. One central hub in the lower forebrain, called the thalamus, distributes the activity to several distinct regions of the cerebral cortex that convey different aspects or “components” of the pain sensation. We can attribute each component to one major brain region, notwithstanding that this is an oversimplification that ignores the distributed, network-like character of all processes in the brain. Actually, there is some debate over whether the sensation of pain entirely emerges up in the cerebral cortex, or whether it instead emerges in raw form below the cortex (perhaps partly in the thalamus) with the cerebral cortex only adding certain components and modulating the pain, e.g., when we cognitively magnify or repress it (Devor 2016 ; Key 2016 ). In any case, as a first approximation, we can distinguish and localize the following components:

The discriminative component: Where is the lesion on the body, and what were the nature and duration of the injury? This can be mostly attributed to the somatosensory area of the cerebral cortex, a region where also other body sensations (touch, pressure, temperature, etc.) are processed.

The cognitive component: What does the pain mean for me, how dangerous is it, and how should I react? This aspect is important for our behavioral response, and it depends heavily on the function of the prefrontal cortex, the most anterior part of the cerebral cortex.

The affective component: This is a scientific name for what we all know from experience—pain hurts and causes suffering. It is the aspect of pain that mostly concerns us here and the subject of the above-mentioned debate over whether pain arises in the cortex or subcortically. The dominant view is that pain affects arise in the parts of the cerebral cortex called the cingulate gyrus, which is a round, belt-shaped ridge on the medial side of the cerebral hemisphere, and the insula, which is a recessed island of the lateral cortex deep to your ear. The alternate view, based on the clinical findings that damage to these two cortical regions does not eliminate the pain but just changes its intensity or the attention one pays to it, is that a significant affective pain component arises subcortically, perhaps partly in the amygdala (see below).

Stress and fear: These reactions are mediated by an almond-shaped nucleus in the depth of the temporal lobe called the “amygdala.” This area has gained much interest in recent years as it is involved in processing all sorts of fear, including pathological forms of anxiety, e.g., claustrophobia (Vadakkan and Siddiqui 2019 ).

Finally, pain causes multiple nonconscious, physiological reactions of the body, beginning with fast withdrawal reflexes (organized within the spinal cord), general arousal, and activation of the sympathetic nervous system for “fight or flight” (mediated by the nuclei within the brain stem), and stress-related hormonal changes (e.g., an increase in cortisol, mediated by a forebrain region underneath the thalamus, called hypothalamus).

The large variety, wide distribution, and functional specialization of different brain areas involved in the generation of pain underline the richness and complexity of this conscious state. This is also visible from the diverse, often challenging clinical situations of severe or chronic pain. Pain (real pain!) can occur by malfunction of the pain system itself, in the complete absence of any lesion. Pain components can dissociate, meaning one can have pain but it does not hurt, or one can suffer from pain but cannot localize or describe it. Interestingly, pain is subject to all of the neuronal mechanisms involved in learning processes: synaptic plasticity, extension of pain-related brain regions, and strengthening of pain sensations by rewards. As a result, pain can become chronic and turn into a genuine pain disease where the pain processing system has become a problem, rather than a protective mechanism. Finally, organ recovery from brain-dead patients may and can be done without anesthesia. This legal and ethical consideration reflects the firm causal link between brain function and pain experience. No brain, no pain.

Why have we described human pain so thoroughly in an article about plants? It was to show that pain processing, if it is anything like our human experience, is a complex phenomenon involving neurons and specialized brain regions—and plants have neither.

Pain in nonhuman animals

All mammals have all the components of the human pain system, from the nociceptors, to the pain pathways, subcortical brain regions, and the various pain-related areas of the cerebral cortex. Thus, it is widely accepted that all mammals can experience pain. None of the other vertebrates—birds, reptiles, amphibians, or fish—has a mammal-like cortex in their cerebrum. This has prompted researchers who assert that pain requires a cerebral cortex to state that non-mammalian vertebrates do not feel pain (Key 2016 ). This statement is controversial, however, because all these vertebrates have the subcortical brain structures involved with nociceptive processing; thus, researchers who assert that pain arises subcortically say all vertebrates can experience pain (Feinberg and Mallatt 2016 , Chapter 8). The argument that pain needs a cerebral cortex has also received much criticism because traits can evolve from multiple alternate structures to the same end (Sneddon and Leach 2016 ). In birds, for example, the enlarged cerebral hemispheres have analogous regions to the mammalian neocortex, in line with their highly advanced cognitive abilities (Güntürkün and Bugnyar 2016 ). Thus, most researchers and government policies that regulate humane treatment of laboratory animals say that all vertebrates feel pain (Committee for Recognition and Alleviation of Pain 2009 ; Mikhalevich and Powell 2020 ).

What about invertebrates? Some of them have complex brains and behaviors, namely, the arthropods such as insects, lobsters, and spiders and cephalopods such as octopuses and squid. These invertebrates have nociceptors, but their brains evolved independently of vertebrate brains and are quite different. Furthermore, the nociceptive processing parts of their brains have not yet been located. To judge if they are conscious, it is necessary to look for the behaviors that associate with pain in the vertebrates and see if these invertebrates perform them. The pain-indicating behaviors are operant learning, from experience, of strategies to avoid noxious stimuli; learning to avoid a place where a noxious stimulus was formerly presented (conditioned place aversion); specific changes in behavior such as rubbing and guarding the wound; and self-delivery of analgesic pain relievers (Feinberg and Mallatt 2016 , pp.150-153; Walters 2018 ; Sneddon 2019 ). Among invertebrate animals, only the cephalopods and many arthropods pass these criteria, and increasing numbers of investigators accept that they feel pain (Elwood 2020 ; Mikhalevich and Powell 2020 ).

Again, what does this have to do with plant pain? No operant learning or conditioned place aversion has ever been demonstrated in plants so they seem to fail those pain tests.

Pain in plants?

Now we can examine more systematically whether plants feel pain. For this, there are two basic questions:

Do plants have nociceptive cells and molecular receptors for noxious stimuli such as ASICs (acid sensing ion channels) or TRPs (transient receptor potential channels), the two most frequently occurring nociceptors in animals (Smith and Lewin 2009 )? In regard to nociceptive sensory cells, the answer is definitely no. In regard to the receptor molecules, the answer is most probably not, but one should bear in mind that plants have receptors and ion channels with similarities to the molecular constituents of animal nociceptive systems. Among these are plant ion channels that alter their gating with pH, similar to ion channels in animals within and outside the nociceptive system. For example, both of the guard cell K + channel families (gated outwardly rectifying potassium channel, GORK; gated inwardly rectifying potassium channel, KAT) are sensitive to pH (Dietrich et al. 2001 ), as are many mammalian K+ channels (Sepúlveda et al. 2015 ). Likewise, both plants (Hamant and Haswell 2017 ) and animals (Jin et al. 2020 ) have mechanoreceptors. In animals, these receptors serve multiple functions from mediating touch to hearing, posture, and balance. While some mechanoreceptors in animals monitor mechanical damage and are thus nociceptive, this does not justify any claim for a nociceptive sensory system in plants just by analogy.

Do plants have a system for integration and experience of damaging stimuli, similar to the complex, highly specialized pain processing network in animals? Definitely not: we reiterate that plants lack both neurons and a brain or any other substrate for central representations of inner states. They therefore cannot experience pain. Advocates of consciousness and cognition in plants point out, however, that plants react to damaging cues with widespread electrical and chemical signals, resembling a coordinated reaction (van Bel et al. 2014 ; Gallé et al. 2015 ). Plants do indeed respond to burning injuries and destructive wounding by “slow wave membrane potentials” (Nguyen et al. 2018 ; Lew et al. 2020 ), by accumulating jasmonate (Pavlovič et al. 2020 ) and releasing various volatile substances (Baluška et al. 2016 ). None of these processes has, however, any similarity to the initiation and distributed processing of pain in animals. An important limitation of electrical signaling in plants is that, as far as we know, it is all one way without any feedback messaging to allow signal exchanges (R. Hedrich, personal communication). Thus, plants have no coordinated network nor center for integrating the specific cues and reactions to damage, in sharp contrast to pain-experiencing animals and humans.

Among the plant neurobiologists, Baluška ( 2016 ) gave the fullest consideration of why plants might experience pain. He provided five possible reasons: (1) stressed plants are known to produce anesthetics, the major ones being ethylene and divinyl ether, and this could be to relieve the plant’s own pain; (2) plants express glutamate and GABA receptors, similar to animal’s neurons; (3) plant roots grow away from danger as if showing a plant version of negative feelings; (4) plants are sensitive to the behavior-suppressing effects of numerous exogenous anesthetics; (5) all living organisms may need pain states to survive in a dangerous world.

None of these reasons seems to hold up. The first argument that a plant makes anesthetics to relieve its own pain may indeed deserve further consideration and experimental investigation. Speaking against it, however, is that the ethylene produced by stress acts more like a plant hormone than an anesthetic, as it has only been shown to signal ordinary, physiological responses (tolerance to wounding, heat, cold, drought, salt); furthermore, ethylene is not only produced under stressful conditions that would require pain relief but also throughout the life cycle to regulate the plant’s growth, development, and senescence (Müller and Munné-Bosch 2015 ; Yang et al. 2015 ; Iqbal et al. 2017 ). Likewise, the other purported “anesthetic,” divinyl ether is tied to pathogen resistance, not to plant neurobiology (Stumpe et al. 2008 ; Fammartino et al. 2010 ). The second argument, that plants possess typical neurotransmitter receptors, is flawed as long as no evidence is produced for information processing in synaptically connected, neural-like networks in plants (more on this later). The third argument, that roots grow away from danger, refers to a merely physiological adaptation, namely, the avoidance response that is present in all organisms including prokaryotes (which most scientists consider to lack feelings: Mallatt and Feinberg 2017 ). Fourth, plants’ susceptibility to exogenous anesthetics is only exemplifying the universal, disengaging effects of these substances on all living organisms, which should not be confounded with their specific actions on nervous systems that affect pain perception, actions, consciousness, and memory (Kelz and Mashour 2019 ). The fifth argument, on the universality of pain states for all living matter, is nothing more than speculation, rooted in the nineteenth century vitalism (Bernard 1878 ; Perouansky 2012 ; Grémiaux et al. 2014 ).

Anesthetics, consciousness, and sleep

General anesthetics not only block the sensation of pain in humans but also alter consciousness. This effect distinguishes them from local anesthetics, which inhibit the excitation of sensory nerve endings by binding to membrane-sodium channels, and from purely analgesic drugs, which act on different levels of the nociceptive system without affecting consciousness. Because the effects of anesthetics on plants are increasingly being used as arguments for plant consciousness, it is important to illuminate the respective mechanisms, which are, not surprisingly, tightly linked to complex functions within the central nervous system. The nonconscious state induced by most general anesthetics has some similarities to sleep, another state of altered consciousness. In popular descriptions, anesthesia is often described as putting the patient to sleep. In this section, we compare these two states for any insights into whether plants have consciousness.

Anesthetic substances can affect consciousness in different ways and degrees, varying from complete loss of consciousness to disconnected states of consciousness where external cues are excluded (resembling a dream experience) or even connected consciousness where some awareness of outer cues is preserved (Bonhomme et al. 2019 ). The underlying mechanism is not a global inhibition of all neuronal signaling but rather a loss of coordination (coupling) between neurons in specific brain areas (Akeju and Brown 2017 ; Kelz and Mashour 2019 ; Hudson 2020 ).

Here are some similarities and differences between the anesthetized and the sleeping brain. Both states involve specific and complex activity patterns in defined brain regions and are, thus, tightly linked to the electrical activity of the nervous tissue. Many anesthetics affect activity in sleep-regulating networks including the hypothalamus, arousal systems in the brain stem, and recurrent cortical-subcortical loops that are essential for consciousness (Bonhomme et al. 2019 ). In all cases, however, the resulting activity patterns under anesthesia deviate from the typical, brain-wide synchronous oscillations characteristic of non-rapid eye movement (non-REM) sleep as well as from the waking-like patterns that characterize REM sleep (Bonhomme et al. 2019 ; Akeju and Brown 2017 ).

Do plants sleep, and could anesthetizing them tell anything about this? Several advocates of plant consciousness have claimed plants do sleep (Bose 1927 ; Barlow 2015 ; Shepherd 2017 ; Lamme 2018 ). This claim can be clearly negated, however. In animals with a complex brain, sleep proceeds through highly specific activity patterns (Purves et al. 2017 ), including different brain states and phases that are accompanied by multiple cognitive (e.g., dreaming in mammals) and physiological (e.g., decreased muscle tone) reactions. Thus, sleep in the sense of altered consciousness requires a highly differentiated central nervous system. What we share with simpler animals like the worm Caenorhabditis elegans is a circadian alteration of nervous activity (Anafi et al. 2019 ). The quiescent phase can be—and often is—called “sleep”, but then it does not have any connotation of consciousness (i.e., of a nonconsciousness that wakes into consciousness). Similarly, plants follow circadian changes of activity. This is obvious in the case of photosynthetic light harvesting, which ceases during the night, and its rhythms involve metabolic, transcriptional, cellular, and system-level mechanisms. As Lefoulon et al. ( 2020 ) have recently shown for plants that have CAM (Crassulacean acid metabolism), the nocturnal cessation of anion channel activity in guard cells is due to a stoppage of channel protein synthesis—a physical rather than a mental (sleeping) explanation. In no way does the ubiquitous presence of the day-night cycle in organisms imply the presence of consciousness. There is no electrophysiological evidence that plants have a sleeping state similar to ours. Because plants do not sleep, they do not have the known-to-be-conscious experiences of REM sleep and waking up. And, without sleep, their responses to anesthetics cannot inform nervous aspects of sleep research.

Anesthetics and plants

Kelz and Mashour ( 2019 ) covered the many molecular targets of general anesthetics, emphasizing those targets that are conserved from single-celled organisms to humans (Fig. 1 ). As we mentioned, the best documented of these targets are many kinds of ion channels, of both the voltage-gated and ligand-gated types. These include “pLGIC” protein channels (pentameric ligand-gated ion channels) such as GABA A (gamma-aminobutyric acid) receptors (Hemmings et al. 2019 ), Na+ channels (Barber et al. 2014 ), K+ channels (MacKinnon et al. 1998 ; Li et al. 2018 ), and Ca 2+ channels. Additionally, the anesthetics probably target the lipid bilayers of cellular plasma membranes (Pavel et al. 2020 ). Many of anesthetics’ “neuron-specific” effects on animals are conserved effects that have been elaborated to disrupt electrical signaling in the nervous system. In their list of conserved effects, Kelz and Mashour ( 2019 ) also included disruption of microtubules of the cell skeleton and inhibition of mitochondrial complex I, although the authors only discussed these effects in animals.

figure 1

Effects of anesthetics in different taxa of organisms. Conserved effects are in the bottom rows (molecular-cellular) and grade to more taxon-specific effects in the middle and top rows. Note that the effects on mitochondrial complex I have only been shown for animals/humans but may well be present in plants and single-celled organisms (see main text). Sources of the illustrations are (1) http://www.biology-resources.com/drawing-paramecium.html (D.G. Mackean); (2) https:www.biologie-seite.de/Biologie/Venusfliegenfalle (William Curtis 1790); (3) Frieda Kahlo painting, 1944 (the broken column showing the results of her spinal surgery for a painful back injury); (4) a fearful cat. Charles Darwin (1872) The expression of emotion in man and animals. John Murray, London

Turning to the effects of anesthetics on plants , the inhibition of electrical signaling has been documented (Yokawa et al. 2018 ; Pavlovič et al. 2020 ) as has a disruption of microtubules (Dustin 2012 ). In addition, considering the basic similarity in structure of the mitochondrial complex I in mammals, yeast, and plants (Davies et al. 2018 ), it is highly likely that substances targeting this complex in mammals also do so in plants. Ion channels, microtubules, and correctly functioning mitochondria are so fundamental to the physiology of plants that their inhibition through anesthetic treatment will inevitably lead to a shutdown of cell function. Therefore, it seems that conserved, general effects of anesthetics could account entirely for plants’ responses to them, and no neuron-like effects need be proposed.

As mentioned, plants have glutamate and GABA signaling and receptors. Animal versions of these receptors are targets of anesthetics in the animal nervous systems, especially at neuron-to-neuron synapses where glutamate and GABA act as neurotransmitters (Kelz and Mashour 2019 ). From this, plant neurobiologists have inferred that plants’ susceptibility to anesthetics reveals that plants have the same types of “neuronal” processes involved in animal consciousness (Baluška 2016 ; Yokawa et al. 2018 ; Trewavas et al. 2020 ). As pointed out by Taiz et al. ( 2020 ), however, this is a giant leap in logic especially because plants do not have true neurons or any equivalents of synapses (claims for “plant synapses” being especially dubious: Robinson et al. 2018 ). A neurotransmitter-like function is questionable for glutamate in plants, where glutamate acts as a multipurpose and far-ranging signal for many different physiological processes, a high fraction of which are not obviously involved in any information processing that could be related to a nervous system (seed germination, root architecture, pollen germination: Qiu et al. 2020 ). The argument that their GABA receptors show plants to have neuron-like GABA signaling is even less convincing because the plant version of this receptor is not homologous to that of animals (Jaiteh et al. 2016 ; Pavlovič et al. 2020 ), with many structural differences. Thus, there is no guarantee (in the absence of direct evidence) that the anesthetics would even bind to the plant GABA receptor, as they bind to the animal version. Recently, the plant neurobiologists acknowledged this GABA-related threat to their claims (Pavlovič et al. 2020 , pp. 180-181), where they also admitted, “. . . it is impossible to identify the protein target of an anesthetic on electrical signals in plants.” De Luccia ( 2012 , p. 1166) admitted the same thing. And without any specific information about targets (the ion channels, etc.), all the claims about anesthesia and plant consciousness are speculation.

In summary, plants lack the structural and functional systems required for anesthetization to reveal anything similar to the consciousness of animals and humans. Anesthetics are drugs whose mechanisms are not as “mysterious” as claimed (Baluška et al. 2016 ; Yokawa and Baluška 2018 ). Like many other drugs, especially with the effects in the central nervous system, they have multiple molecular targets and complex systemic effects. It is clear, however, that they disrupt the brain-wide coordinated neuronal activity patterns required for conscious experience and action (Kelz and Mashour 2019 ). This does not, and cannot, happen in plants where the actions of anesthetics can be explained as mere biochemical and biophysical effects. Similarly, if plants were to show biochemical reactions to antidepressant or antipsychotic drugs, we would not tend to believe that they suffer from depression or schizophrenia.

We conclude that plants do not possess the molecular and structural machinery for pain generation. For anesthetics, there is indeed evidence that these substances affect plants’ non-neural, physiological processes like electrical signaling, growth movements, germination, and multiple biochemical reactions. Taking these effects as evidence for consciousness in plants is, however, an argument without any scientific foundation (Fig. 2 ). The lack of consciousness also precludes the use of plants as model organisms for studying systemic effects of anesthetics in that context. We therefore cannot agree with Baluška and Reber ( 2019 ) who consider the model plant Arabidopsis thaliana as an ideal experimental system for studying anesthetics and consciousness. At the very most, studies on plants might aid in unravelling specific molecular or cellular functions of anesthetics, although we are not aware of any prominent example. Studying anesthetics in animals and humans, in contrast, is a flourishing branch of neuroscience and medicine, and all required methods, models, preparations, and conceptual tools are available. From a medical and neuroscience perspective, drugs acting on conscious experience should be foremost studied in organisms possessing consciousness. From a plant-science perspective, experiments on anesthetics in plants do not deliver any information relevant to the question of plant intelligence or consciousness.

figure 2

Effects of general anesthetics on plants versus animals. The top half shows the shared effects on plants and on all animals, whereas the bottom half shows that they affect consciousness and pain in certain animals with complex nervous systems. Dotted arrow indicates how plant neurobiologists speculate without evidence that the anesthetics cause the same consciousness-diminishing effects on plants. However, the basic, shared effects can account for plants’ responses without any need to invoke plant consciousness

Data availability

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Draguhn, A., Mallatt, J.M. & Robinson, D.G. Anesthetics and plants: no pain, no brain, and therefore no consciousness. Protoplasma 258 , 239–248 (2021). https://doi.org/10.1007/s00709-020-01550-9

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Anesthetics and plants: no pain, no brain, and therefore no consciousness

Affiliations.

  • 1 Institute for Physiology and Pathophysiology, Medical Faculty, University of Heidelberg, 69120, Heidelberg, Germany.
  • 2 The University of Washington WWAMI Medical Education Program, The University of Idaho, Moscow, ID, 83844, USA.
  • 3 Centre for Organismal Studies, University of Heidelberg, Im Neuenheimer Feld 230, D-69120, Heidelberg, Germany. [email protected].
  • PMID: 32880005
  • PMCID: PMC7907021
  • DOI: 10.1007/s00709-020-01550-9

Plants have a rich variety of interactions with their environment, including adaptive responses mediated by electrical signaling. This has prompted claims that information processing in plants is similar to that in animals and, hence, that plants are conscious, intelligent organisms. In several recent reports, the facts that general anesthetics cause plants to lose their sensory responses and behaviors have been taken as support for such beliefs. These lipophilic substances, however, alter multiple molecular, cellular, and systemic functions in almost every organism. In humans and other animals with complex brains, they eliminate the experience of pain and disrupt consciousness. The question therefore arises: do plants feel pain and have consciousness? In this review, we discuss what can be learned from the effects of anesthetics in plants. For this, we describe the mechanisms and structural prerequisites for pain sensations in animals and show that plants lack the neural anatomy and all behaviors that would indicate pain. By explaining the ubiquitous and diverse effects of anesthetics, we discuss whether these substances provide any empirical or logical evidence for "plant consciousness" and whether it makes sense to study the effects of anesthetics on plants for this purpose. In both cases, the answer is a resounding no.

Keywords: Cognition; General anesthetics; Ion channels; Perception; Sleep.

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Effects of anesthetics in different…

Effects of anesthetics in different taxa of organisms. Conserved effects are in the…

Effects of general anesthetics on…

Effects of general anesthetics on plants versus animals. The top half shows the…

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Do Plants Feel Pain?

Plant seedlings emerging from rich fertile soil

Given that plants do not have pain receptors, nerves , or a brain , they do not feel pain as we members of the animal kingdom understand it. Uprooting a carrot or trimming a hedge is not a form of botanical torture, and you can bite into that apple without worry. However, it seems that many plants can perceive and communicate physical stimuli and damage in ways that are more sophisticated than previously thought.

Some plants have obvious sensory abilities, such as the Venus flytrap and its incredible traps that can close in about half a second. Similarly, the sensitive plant rapidly collapses its leaves in response to touch, an adaptation that might serve to startle away potential herbivores . While these plants visibly display a clear sensory capacity, recent research has shown that other plants are able to perceive and respond to mechanical stimuli at a cellular level. Arabidopsis (a mustard plant commonly used in scientific studies) sends out electrical signals from leaf to leaf when it is being eaten by caterpillars or aphids , signals to ramp up its chemical defenses against herbivory. While this remarkable response is initiated by physical damage, the electrical warning signal is not equivalent to a pain signal, and we should not anthropomorphize an injured plant as a plant in pain. Plants have exceptional abilities to respond to sunlight, gravity, wind, and even tiny insect bites, but (thankfully) their evolutionary successes and failures have not been shaped by suffering, just simple life and death.

Do Plants Feel Pain?

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Published Online : Jul 15, 2020

Page range: 71 - 98, doi: https://doi.org/10.2478/disp-2020-0003, keywords plants , pain , moral patient , phenomenal consciousness , qualia, © 2020 adam hamilton et al., published by sciendo, this work is licensed under the creative commons attribution-noncommercial-noderivatives 3.0 license..

Many people are attracted to the idea that plants experience phenomenal conscious states like pain, sensory awareness, or emotions like fear. If true, this would have wide-ranging moral implications for human behavior, including land development, farming, vegetarianism, and more. Determining whether plants have minds relies on the work of both empirical disciplines and philosophy. Epistemology should settle the standards for evidence of other minds, and science should inform our judgment about whether any plants meet those standards. We argue that evidence for other minds comes either from testimony, behavior, anatomy/physiology, or phylogeny. However, none of these provide evidence that plants have conscious mental states. Therefore, we conclude that there is no evidence that plants have minds in the sense relevant for morality.

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Do Plants Feel Pain? No, and Here’s How Scientists Know

It’s a question people love to throw at vegans and vegetarians — so here’s a thorough explanation.

A closeup of two hands holding produce

Explainer • Science • Sentience

Seth Millstein

Words by Seth Millstein

When vegans and vegetarians argue against eating meat because of the pain it inflicts on animals, they’re often met with a pithy-sounding retort: What if plants feel pain , too? You can’t prove that they don’t, the argument goes, so isn’t a plant-based diet potentially inflicting just as much pain as a meat-based one?

It’s a common argument, but it isn’t a good one. Plants are incredibly complex organisms, and scientists have made some extraordinary discoveries in recent years about how plants  process and respond to external stimuli . However, absolutely nothing that we know about plants suggests that they’re capable of feeling pain, or anything similar to the sensation we know as pain. Here’s why.

How Scientists Define  Pain in the First Place

At its core, pain is a warning system — your body’s way of prompting you to make changes to your circumstances  to avoid injury.

The experience of pain is closely associated with a type of nerve ending called a nociceptor. When the body is exposed to  potentially injurious stimuli — an extreme temperature or laceration, for instance — nociceptors communicate this to the brain , and the brain in turn creates a pain sensation.

There are certain rare situations wherein it’s possible to experience pain without nociceptors; the classic example is phantom limb pain, when an amputee feels pain in a limb that they no longer have. Phantom limb pain is a poorly understood condition that perplexes scientists to this day, but it is relevant to the question of plant pain, as we’ll see in a moment.

Do Plants Feel Pain?

In short, no. It’s notoriously difficult to prove the non-existence of something , and doubly so when that thing is a subjective experience like pain. That said, almost everything we know about plants suggests that they aren’t capable of feeling pain — or anything, for that matter.

For one, plants don’t have nociceptors, nervous systems or brains. In species that do experience pain, the nervous system and the brain are both integral to that experience: the nervous system detects a noxious stimulus, and the brain creates the sensation of pain when it receives this message from the nervous system.

As mentioned earlier, the existence of phantom limb pain means that it is possible for someone to experience pain without having nociceptors at the site of the pain. But it’s not possible to experience phantom limb pain without a brain and a nervous system, and the phenomenon of phantom limb pain suggests that pain is ultimately constructed in the brain .

“Plants definitely perceive and respond to touch and temperature changes, but I am disinclined to say they ‘feel,’” Dr. Elizabeth Van Volkenburgh, a plant biologist, wrote in Psychology Today. “The whole business of feeling relies on a brain, and plants don’t have brains.”

If Plants Don’t Feel Pain, Why Do They React to Danger?

As Van Volkenburgh notes, plants are able to respond to external stimuli. We’ve all seen time-lapse videos of flowers rotating throughout the day to make sure they’re always facing the sun, but plant reactions go beyond this. Many plants emit chemicals when they’re cut or damaged, for instance; these chemicals can serve various purposes, from warning other nearby plants of the danger to poisoning whoever is causing the damage.

In other words, when plants are exposed to something threatening, they will sometimes respond in ways that, to our eyes, look a lot like a reaction to pain. And it’s true that pain is sometimes measured by observing how an organism reacts to ostensibly painful stimuli in their environment; if a friend stubs their toe and starts screaming in agony, for instance, you might reasonably conclude that they’re in pain.

But the fact that plants sometimes behave in ways that we associate with pain doesn’t prove that they’re actually feeling pain, because behavior doesn’t always correlate with experience in expected ways. It’s possible for an organism to be in pain without changing its behavior; chickens are notorious for hiding their pain when sick or injured, for instance. And it’s easy to act like you’re in pain when you aren’t, as demonstrated by this video of a cat pretending to be injured in order to convince someone to let them inside their house.

The way plants respond to injuries isn’t an example of pain, but rather, an example of a defense mechanism. Plants, like humans, have evolved ways to defend themselves against external threats, and while our defense involves a pain sensation, theirs does not. One could even argue that plants, in this one very specific sense, are more highly evolved than we are: they can effectively defend themselves against harm without experiencing unpleasant feelings of physical agony.

Why Animal Pain Is Different Than Plant Pain

If pain can never be directly observed, only experienced and inferred, how can we ever know that another organism is in pain?

In the most narrow technical sense, we can’t. But in the most narrow technical sense, we also can’t even be sure that other people exist — so scientists take a slightly less philosophical, more holistic approach when attempting to determine whether other animals can feel pain.

Generally speaking, scientists infer that  animals feel pain using a few different tools — namely, existing knowledge of the human experience and how humans traditionally react to pain, observations of  animal responses to potentially injurious stimuli or events, and the presence or absence of pain receptors, nervous systems and brains in said animals.

Using these tools, scientists have concluded that most  animals do feel pain , including not only mammals but also fish, reptiles, and even some decapods like lobsters and crabs. These animals are very dissimilar from each other, but they  all have two big things in common: nervous systems and brains. Plants lack both, and scientists have thus been unable to conclude that they’re able to feel pain.

If Plants Can’t Feel Pain, Why Should We Care About Them?

It’s absolutely crucial to point out that just because plants can’t feel pain doesn’t mean we should view them as disposable or unimportant. On the contrary: plants are extremely, extremely important. In the most literal sense possible, we would all be dead without them.

If not for plants, we wouldn’t be able to breathe, as they’re the ones that oxygenate the air around us. Without plants, we’d starve to death — not just because we eat them, but because the animals that many people  eat also eat them. Plants play a crucial role in keeping the planet’s temperatures within a livable range, and are essential ingredients in as much as 40 percent of the medications people use every day.

There are plenty of other vital purposes plants serve, but the point is clear: just because plants don’t feel pain, doesn’t mean they don’t matter. They most definitely do.

The Bottom Line

The reason plants can’t feel pain is because they lack nervous systems and brains. This is also the precise reason why so many nonhuman animals, including the many that we kill by the millions   every day for food, can and do feel pain. To understand why plants can’t feel pain is to understand why animals can. Wider recognition of this difference should arguably  lead more people to more seriously consider animals’ experiences of pain when deciding what to eat.

Independent Journalism Needs You

Seth Millstein is a writer and musician living in the Bay Area. He has helped launch several early-stage journalism startups, including Bustle and Timeline, and his work has been published in Bustle, Huffington Post, The Daily Dot and elsewhere.

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Do Plants Feel Pain? What We Know About Plants’ ‘Distress Signal’

Plants are often considered to be silent and passive organisms that merely react to their environment.

However, recent research has revealed that plants are capable of complex signaling and communication systems that allow them to sense and respond to various stimuli, including potential threats.

In this article, we will explore the fascinating question of whether plants feel pain, and how they use chemical and acoustic signals to convey their distress and defend themselves.

How Plants Sense and Respond to Stress (Photo : GUILLAUME SOUVANT/AFP via Getty Images)

Pain perception  is typically associated with living organisms that possess a nervous system, which includes specialized sensory receptors, neurons and regions of the brain responsible for processing sensory information.

Plants do not have a brain or nervous system, but they do exhibit intricate biochemical pathways and plant-signaling molecules like hormones that enable them to adapt to their environment.

Plants use a variety of chemical and electrical signals to sense changes in light, gravity, temperature and touch.

They can also respond to external stimuli by growing toward or away from them, adjusting their root and shoot growth and producing defense compounds against predators.

These responses are managed by a complex biological network that coordinates the activities of different cells and tissues.

One of the most remarkable examples of plant signaling is the release of volatile organic compounds (VOCs) that can serve multiple functions.

VOCs are airborne molecules that can travel over long distances and affect the behavior of other organisms.

For instance, plants can use VOCs to attract pollinators, repel herbivores, poison enemies, recruit allies, warn neighboring plants or even communicate with themselves.

The smell we associate with freshly cut grass is actually a chemical distress call, one used by plants to beg nearby critters to save them from attack (usually it's an affront by insects, but in this case, it's lawnmower blades). This defense response beckons the question: Do plants feel pain?

Also Read:   Fish Do Not Feel Pain, Say Scientists

How Plants Emit Ultrasonic Sounds When in Distress

The answer to whether plants feel pain is not straightforward, as they do not feel pain like us humans do, but some plant scientists posit that they may feel pain in their own way.

One of the most intriguing evidence  for this hypothesis is the discovery that some plants can emit ultrasonic sounds when they experience environmental stress.

A team of scientists from Tel Aviv University found that tobacco plants and tomato plants can produce high-frequency distress sounds that are between 20 and 100 kilohertz, which they believed could convey their distress to other organisms and plants within the vicinity.

The researchers tested the plants by not watering them and by cutting off their stems. They then recorded their response with a microphone that was placed 10 centimeters away.

In both cases, the scientists found that the plants began to emit ultrasonic sounds that varied in intensity and frequency depending on the type and severity of the stress.

When the stem of a tomato plant was cut, the researches found it emitted 25 ultrasonic distress sounds over the course of an hour. The tobacco plants that had their stem cut sent out 15 distress sounds.

When the team of scientists deprived each plant of water, the tomato plants emitted even more distress sounds, increasing to 35 in one hour, while the tobacco plants made 11.

The team of scientists wrote in their paper that these findings can alter the way that we think about the plant kingdom, which has been considered to be almost silent and not given much thought.

The researchers used the data that they had gathered in a machine learning model to be able to predict the different frequency of sound that plants may emit under other conditions like heavy rain or wind.

The team scientists believe that listening to the different types of sounds that are emitted by plants could help with precision agriculture, and it can allow farmers to identify any potential issue with their crops.

Related article:   Plants May Be Able to See, Scientists Discover

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Do Plants Feel Pain? Exploring the Science and Debate

 May 9th , 2024

CHIRANJIT MITRA

Can plants feel pain like humans and animals? This question sparks debate within the scientific community and among plant lovers.

Human pain involves sensory receptors, a nervous system, and awareness. Plants lack these structures.

How Do We Define Pain?

Plants respond to injuries, light changes, and threats by releasing chemicals and altering growth patterns.

Plants DO React

These responses are survival mechanisms. Scientists debate whether they are the same as feeling pain.

But Is It Pain?

Controversial studies suggest some anesthetics dull plant responses. However, this doesn't prove pain.

Anesthetics and Plants?

If plants could feel pain, it would impact how we treat them, from gardening to agriculture.

The Ethical Question

While research continues, there's no clear consensus on whether plants experience conscious pain.

The Ongoing Debate

The question of plant sentience raises fascinating ethical and philosophical discussions.

What do YOU think?

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Do plants really feel pain what does science say.

Do Plants Really Feel Pain? What Does Science Say?

Do plants really feel pain? Every now and then, a story will make the rounds on news sites and social media sharing the findings of a study that allegedly uncovered that plants, like animals, experience pain. These articles typically leverage the findings to push back at the ethics of not eating animals as if to say, if plants feel pain, then it’s really the same as eating meat , dairy , and eggs .

These articles often cherry-pick findings from actual scientific studies which show certain capabilities of plants, but is the argument that plants feel pain really accurate? The way these studies are reported in the media can be quite biased, drawing conclusions from the research that the original authors never mentioned.

Can Plants Hear Themselves Being Eaten?

An oft referenced study is a 2014 study published in the journal Oecologia that was undertaken at the University of Missouri. Researchers found that a certain species of plant released defense chemicals that made it less appealing to herbivorous creatures in response to the sound vibrations of caterpillars munching on it.

Do Plants Really Feel Pain? What Does Science Say?

The Sun newspaper reported on this study, the headline to the piece crowing, “what are the veggies going to eat now?” The article claimed that plants “know” when they are about to be eaten, and are “not happy” about it. Business Insider news website also published an article on this study, opening with “vegetarians and vegans pay heed,”  before going onto say that plants “don’t like it” when they are eaten.

The scientific study which these assumptions have been drawn from, predictably, makes no such claims suggesting that plants are as consciousness or as sentient as farm animals. While plants were able to differentiate between the vibrations caused by an insect dining and the rustle caused by wind, the study states that “the ecological significance of these responses is unclear.”

One of the researchers who conducted the study, Dr. Heidi Appel, summarized their findings as follows; “We found that feeding vibrations signal changes in the plant cells’ metabolism, creating more defensive chemicals that can repel attacks from caterpillars.”

Do Plants Really Feel Pain?

Our current understanding of pain involves sensory and emotional, both subjective components. Analogous neurological structures (for example, specialized pain receptors, also called nociceptors) are found in both human and non-human animals, according to a 2009 study in the National Academies Press .

research on plants feeling pain

Studies have also shown that animals are likely to experience the emotional, subjective components of pain. No matter what the animal – dog, cow, pig, cat, bird, etc – most will respond to pain in a physical sense. Unlike animals , plants don’t have a central nervous system or brain. If they did, then they might run away from or fight back against insects or machines that harvest them, like in the case of animals who have escaped slaughterhouse trucks.

Plants, however, do not have such analogous structures. Plants can respond to stimuli, like the aforementioned species that released unsavory chemicals while being eaten by an insect or they can turn towards the sunlight. While plants are rooted, videos show that they do move around throughout the day. But, they don’t have the same fight-or-flight response to the threat of pain or death that humans and non-human animals have. And there is no scientific evidence to show that they can “feel” in the same way as humans and other animals can.

Professor Daniel Chamovitz, Dean of the Faculty of Life Sciences at Tel Aviv University, is a plant scientist who had conducted extensive research into how plants experience the world. He has even written a popular book on the topic: 2013’s “ What a Plant Knows: A Field Guide to the Senses .” Although Professor Chamovitz often talks about plant feelings, stating that they are not the inanimate objects that many believe they are, he acknowledged in an interview that “a plant can’t suffer subjective pain in the absence of a brain, I also don’t think that it thinks.”

Speaking to how plants function, he said, “If you think about it, rootedness is a huge evolutionary constraint. It means that plants can’t escape a bad environment, can’t migrate in the search of food or a mate. So plants had to develop incredibly sensitive and complex sensory mechanisms that would let them survive in ever changing environments.”

In a nutshell, plants are able to sense things like sound, sun, and even smell as an evolutionary necessity because they are largely immobile. Additionally, animal right nonprofit Mercy for Animals notes that plants have no nociceptors, the specific receptors that allow humans and animals to feel pain.

research on plants feeling pain

Do Plants and Animals ‘Feel’ the Same Way?

Animals, on the other hand, are wholly capable of experiencing and responding to pain and stimuli. According to the International Association for the Study of Pain (IASP), pain is “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.” 

The definition, which is technically applicable to humans, emphasizes the importance of self-reporting pain – think the charts at a doctor’s office, a scale of one to ten, etc. Even the IASP acknowledges that measuring pain can’t be pinned down to an exact science, as different people will have different definitions of what a pain level is. One person’s “severe” could be another’s “moderate.”

And while animals can’t verbalize their pain in the same way that humans do, it doesn’t mean that they don’t experience it. Due to advancements in science, techniques such as Judgement Bias Testing (JBT) show that animals experience pain in a way similar to humans – not plants, as coverage of the “plants feel pain” study implies.

What JBT does is measure an individual’s “affective state,” or emotional state through how they respond to ambiguous situations. This can be applied to animals through training them to associate tasks with positive or negative outcomes. For example, one study involving dairy calves aimed to uncover if the animals were in a negative headspace following disbudding, a method of dehorning young cattle that involves use of a hot iron.

research on plants feeling pain

In the study, titled “Pain and Pessimism,” researchers trained calves to learn that if calves touched a red computer screen with their nose, they would be rewarded with milk. If the screen was white, they received nothing. Calves quickly learned the correlation and would touch the screens when red, but ignore it when the screen went white.

After that, researchers introduced the more ambiguous dark pink and light pink screens – and found that calves were more likely to touch dark pink screens. The calves then underwent hot-iron disbudding before being exposed to the colored screens again. After the painful experience, calves were less likely to respond to pink screens. Researchers concluded that the traumatic experience had a negative affect on the animals’ mental state.

For the trial, calves were given an anesthetic but in many countries, including Australia, Denmark, and New Zealand, no local anesthetic is required for calves under a certain age. It can be speculated that if the calves’ pain wasn’t numbed at all, then the effects on their mental state would be greater.

Plants, however, can’t be given the same treatment as calves – while they may respond to different levels of light, flora wouldn’t respond when presented with the same options as dairy calves.

Science is always evolving and advancing (that’s part of what makes it so great!), so it may be the case that in years to come we find out that plants are sentient in their own way, and if that day comes we may have to think about how we treat them. However, in terms of our current scientific understanding, there are clear differences between plants and animals as mentioned above.

Even if, in an unlikely future scenario, plants are found to have “feelings” similar to animals, using it as a counterargument against a eating animals is a moot point because livestock raised for meat, dairy, eggs, etc, are fed plants.

It is estimated that “for every 1 kg of high-quality animal protein produced, livestock are fed about 6 kg of plant protein,”  according to the study “Sustainability of meat-based and plant-based diets and the environment.”

If this is the case then many more plants are killed to feed an animal up to slaughter weight, and then kill and eat the animal, than to just kill and eat the plants ourselves. When it comes to soybeans – a staple ingredient used to make tofu, tempeh, and more modern plant-based meat – 98 percent of the crop grown in the US is actually used to feed livestock.

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The Intelligent Plant

Plants have electrical and chemical signalling systems may possess memory and exhibit brainy behavior in the absence of...

In 1973, a book claiming that plants were sentient beings that feel emotions, prefer classical music to rock and roll, and can respond to the unspoken thoughts of humans hundreds of miles away landed on the New York Times best-seller list for nonfiction. “The Secret Life of Plants,” by Peter Tompkins and Christopher Bird, presented a beguiling mashup of legitimate plant science, quack experiments, and mystical nature worship that captured the public imagination at a time when New Age thinking was seeping into the mainstream. The most memorable passages described the experiments of a former C.I.A. polygraph expert named Cleve Backster, who, in 1966, on a whim, hooked up a galvanometer to the leaf of a dracaena, a houseplant that he kept in his office. To his astonishment, Backster found that simply by imagining the dracaena being set on fire he could make it rouse the needle of the polygraph machine, registering a surge of electrical activity suggesting that the plant felt stress. “Could the plant have been reading his mind?” the authors ask. “Backster felt like running into the street and shouting to the world, ‘Plants can think!’ ”

Backster and his collaborators went on to hook up polygraph machines to dozens of plants, including lettuces, onions, oranges, and bananas. He claimed that plants reacted to the thoughts (good or ill) of humans in close proximity and, in the case of humans familiar to them, over a great distance. In one experiment designed to test plant memory, Backster found that a plant that had witnessed the murder (by stomping) of another plant could pick out the killer from a lineup of six suspects, registering a surge of electrical activity when the murderer was brought before it. Backster’s plants also displayed a strong aversion to interspecies violence. Some had a stressful response when an egg was cracked in their presence, or when live shrimp were dropped into boiling water, an experiment that Backster wrote up for the International Journal of Parapsychology , in 1968.

In the ensuing years, several legitimate plant scientists tried to reproduce the “Backster effect” without success. Much of the science in “The Secret Life of Plants” has been discredited. But the book had made its mark on the culture. Americans began talking to their plants and playing Mozart for them, and no doubt many still do. This might seem harmless enough; there will probably always be a strain of romanticism running through our thinking about plants. (Luther Burbank and George Washington Carver both reputedly talked to, and listened to, the plants they did such brilliant work with.) But in the view of many plant scientists “The Secret Life of Plants” has done lasting damage to their field. According to Daniel Chamovitz, an Israeli biologist who is the author of the recent book “What a Plant Knows,” Tompkins and Bird “stymied important research on plant behavior as scientists became wary of any studies that hinted at parallels between animal senses and plant senses.” Others contend that “The Secret Life of Plants” led to “self-censorship” among researchers seeking to explore the “possible homologies between neurobiology and phytobiology”; that is, the possibility that plants are much more intelligent and much more like us than most people think—capable of cognition, communication, information processing, computation, learning, and memory.

The quotation about self-censorship appeared in a controversial 2006 article in Trends in Plant Science proposing a new field of inquiry that the authors, perhaps somewhat recklessly, elected to call “plant neurobiology.” The six authors—among them Eric D. Brenner, an American plant molecular biologist; Stefano Mancuso, an Italian plant physiologist; František Baluška, a Slovak cell biologist; and Elizabeth Van Volkenburgh, an American plant biologist—argued that the sophisticated behaviors observed in plants cannot at present be completely explained by familiar genetic and biochemical mechanisms. Plants are able to sense and optimally respond to so many environmental variables—light, water, gravity, temperature, soil structure, nutrients, toxins, microbes, herbivores, chemical signals from other plants—that there may exist some brainlike information-processing system to integrate the data and coördinate a plant’s behavioral response. The authors pointed out that electrical and chemical signalling systems have been identified in plants which are homologous to those found in the nervous systems of animals. They also noted that neurotransmitters such as serotonin, dopamine, and glutamate have been found in plants, though their role remains unclear.

Hence the need for plant neurobiology, a new field “aimed at understanding how plants perceive their circumstances and respond to environmental input in an integrated fashion.” The article argued that plants exhibit intelligence, defined by the authors as “an intrinsic ability to process information from both abiotic and biotic stimuli that allows optimal decisions about future activities in a given environment.” Shortly before the article’s publication, the Society for Plant Neurobiology held its first meeting, in Florence, in 2005. A new scientific journal, with the less tendentious title Plant Signaling & Behavior, appeared the following year.

Depending on whom you talk to in the plant sciences today, the field of plant neurobiology represents either a radical new paradigm in our understanding of life or a slide back down into the murky scientific waters last stirred up by “The Secret Life of Plants.” Its proponents believe that we must stop regarding plants as passive objects—the mute, immobile furniture of our world—and begin to treat them as protagonists in their own dramas, highly skilled in the ways of contending in nature. They would challenge contemporary biology’s reductive focus on cells and genes and return our attention to the organism and its behavior in the environment. It is only human arrogance, and the fact that the lives of plants unfold in what amounts to a much slower dimension of time, that keep us from appreciating their intelligence and consequent success. Plants dominate every terrestrial environment, composing ninety-nine per cent of the biomass on earth. By comparison, humans and all the other animals are, in the words of one plant neurobiologist, “just traces.”

The Intelligent Plant

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Many plant scientists have pushed back hard against the nascent field, beginning with a tart, dismissive letter in response to the Brenner manifesto, signed by thirty-six prominent plant scientists (Alpi et al., in the literature) and published in Trends in Plant Science . “We begin by stating simply that there is no evidence for structures such as neurons, synapses or a brain in plants,” the authors wrote. No such claim had actually been made—the manifesto had spoken only of “homologous” structures—but the use of the word “neurobiology” in the absence of actual neurons was apparently more than many scientists could bear.

“Yes, plants have both short- and long-term electrical signalling, and they use some neurotransmitter-like chemicals as chemical signals,” Lincoln Taiz, an emeritus professor of plant physiology at U.C. Santa Cruz and one of the signers of the Alpi letter, told me. “But the mechanisms are quite different from those of true nervous systems.” Taiz says that the writings of the plant neurobiologists suffer from “over-interpretation of data, teleology, anthropomorphizing, philosophizing, and wild speculations.” He is confident that eventually the plant behaviors we can’t yet account for will be explained by the action of chemical or electrical pathways, without recourse to “animism.” Clifford Slayman, a professor of cellular and molecular physiology at Yale, who also signed the Alpi letter (and who helped discredit Tompkins and Bird), was even more blunt. “ ‘Plant intelligence’ is a foolish distraction, not a new paradigm,” he wrote in a recent e-mail. Slayman has referred to the Alpi letter as “the last serious confrontation between the scientific community and the nuthouse on these issues.” Scientists seldom use such language when talking about their colleagues to a journalist, but this issue generates strong feelings, perhaps because it smudges the sharp line separating the animal kingdom from the plant kingdom. The controversy is less about the remarkable discoveries of recent plant science than about how to interpret and name them: whether behaviors observed in plants which look very much like learning, memory, decision-making, and intelligence deserve to be called by those terms or whether those words should be reserved exclusively for creatures with brains.

No one I spoke to in the loose, interdisciplinary group of scientists working on plant intelligence claims that plants have telekinetic powers or feel emotions. Nor does anyone believe that we will locate a walnut-shaped organ somewhere in plants which processes sensory data and directs plant behavior. More likely, in the scientists’ view, intelligence in plants resembles that exhibited in insect colonies, where it is thought to be an emergent property of a great many mindless individuals organized in a network. Much of the research on plant intelligence has been inspired by the new science of networks, distributed computing, and swarm behavior, which has demonstrated some of the ways in which remarkably brainy behavior can emerge in the absence of actual brains.

“If you are a plant, having a brain is not an advantage,” Stefano Mancuso points out. Mancuso is perhaps the field’s most impassioned spokesman for the plant point of view. A slight, bearded Calabrian in his late forties, he comes across more like a humanities professor than like a scientist. When I visited him earlier this year at the International Laboratory of Plant Neurobiology, at the University of Florence, he told me that his conviction that humans grossly underestimate plants has its origins in a science-fiction story he remembers reading as a teen-ager. A race of aliens living in a radically sped-up dimension of time arrive on Earth and, unable to detect any movement in humans, come to the logical conclusion that we are “inert material” with which they may do as they please. The aliens proceed ruthlessly to exploit us. (Mancuso subsequently wrote to say that the story he recounted was actually a mangled recollection of an early “Star Trek” episode called “Wink of an Eye.”)

In Mancuso’s view, our “fetishization” of neurons, as well as our tendency to equate behavior with mobility, keeps us from appreciating what plants can do. For instance, since plants can’t run away and frequently get eaten, it serves them well not to have any irreplaceable organs. “A plant has a modular design, so it can lose up to ninety per cent of its body without being killed,” he said. “There’s nothing like that in the animal world. It creates a resilience.”

Indeed, many of the most impressive capabilities of plants can be traced to their unique existential predicament as beings rooted to the ground and therefore unable to pick up and move when they need something or when conditions turn unfavorable. The “sessile life style,” as plant biologists term it, calls for an extensive and nuanced understanding of one’s immediate environment, since the plant has to find everything it needs, and has to defend itself, while remaining fixed in place. A highly developed sensory apparatus is required to locate food and identify threats. Plants have evolved between fifteen and twenty distinct senses, including analogues of our five: smell and taste (they sense and respond to chemicals in the air or on their bodies); sight (they react differently to various wavelengths of light as well as to shadow); touch (a vine or a root “knows” when it encounters a solid object); and, it has been discovered, sound. In a recent experiment, Heidi Appel, a chemical ecologist at the University of Missouri, found that, when she played a recording of a caterpillar chomping a leaf for a plant that hadn’t been touched, the sound primed the plant’s genetic machinery to produce defense chemicals. Another experiment, done in Mancuso’s lab and not yet published, found that plant roots would seek out a buried pipe through which water was flowing even if the exterior of the pipe was dry, which suggested that plants somehow “hear” the sound of flowing water.

The sensory capabilities of plant roots fascinated Charles Darwin, who in his later years became increasingly passionate about plants; he and his son Francis performed scores of ingenious experiments on plants. Many involved the root, or radicle, of young plants, which the Darwins demonstrated could sense light, moisture, gravity, pressure, and several other environmental qualities, and then determine the optimal trajectory for the root’s growth. The last sentence of Darwin’s 1880 book, “The Power of Movement in Plants,” has assumed scriptural authority for some plant neurobiologists: “It is hardly an exaggeration to say that the tip of the radicle . . . having the power of directing the movements of the adjoining parts, acts like the brain of one of the lower animals; the brain being seated within the anterior end of the body, receiving impressions from the sense organs and directing the several movements.” Darwin was asking us to think of the plant as a kind of upside-down animal, with its main sensory organs and “brain” on the bottom, underground, and its sexual organs on top.

“Why did we buy such huge furniture”

Scientists have since found that the tips of plant roots, in addition to sensing gravity, moisture, light, pressure, and hardness, can also sense volume, nitrogen, phosphorus, salt, various toxins, microbes, and chemical signals from neighboring plants. Roots about to encounter an impenetrable obstacle or a toxic substance change course before they make contact with it. Roots can tell whether nearby roots are self or other and, if other, kin or stranger. Normally, plants compete for root space with strangers, but, when researchers put four closely related Great Lakes sea-rocket plants ( Cakile edentula ) in the same pot, the plants restrained their usual competitive behaviors and shared resources.

Somehow, a plant gathers and integrates all this information about its environment, and then “decides”—some scientists deploy the quotation marks, indicating metaphor at work; others drop them—in precisely what direction to deploy its roots or its leaves. Once the definition of “behavior” expands to include such things as a shift in the trajectory of a root, a reallocation of resources, or the emission of a powerful chemical, plants begin to look like much more active agents, responding to environmental cues in ways more subtle or adaptive than the word “instinct” would suggest. “Plants perceive competitors and grow away from them,” Rick Karban, a plant ecologist at U.C. Davis, explained, when I asked him for an example of plant decision-making. “They are more leery of actual vegetation than they are of inanimate objects, and they respond to potential competitors before actually being shaded by them.” These are sophisticated behaviors, but, like most plant behaviors, to an animal they’re either invisible or really, really slow.

The sessile life style also helps account for plants’ extraordinary gift for biochemistry, which far exceeds that of animals and, arguably, of human chemists. (Many drugs, from aspirin to opiates, derive from compounds designed by plants.) Unable to run away, plants deploy a complex molecular vocabulary to signal distress, deter or poison enemies, and recruit animals to perform various services for them. A recent study in Science found that the caffeine produced by many plants may function not only as a defense chemical, as had previously been thought, but in some cases as a psychoactive drug in their nectar. The caffeine encourages bees to remember a particular plant and return to it, making them more faithful and effective pollinators.

One of the most productive areas of plant research in recent years has been plant signalling. Since the early nineteen-eighties, it has been known that when a plant’s leaves are infected or chewed by insects they emit volatile chemicals that signal other leaves to mount a defense. Sometimes this warning signal contains information about the identity of the insect, gleaned from the taste of its saliva. Depending on the plant and the attacker, the defense might involve altering the leaf’s flavor or texture, or producing toxins or other compounds that render the plant’s flesh less digestible to herbivores. When antelopes browse acacia trees, the leaves produce tannins that make them unappetizing and difficult to digest. When food is scarce and acacias are overbrowsed, it has been reported, the trees produce sufficient amounts of toxin to kill the animals.

Perhaps the cleverest instance of plant signalling involves two insect species, the first in the role of pest and the second as its exterminator. Several species, including corn and lima beans, emit a chemical distress call when attacked by caterpillars. Parasitic wasps some distance away lock in on that scent, follow it to the afflicted plant, and proceed to slowly destroy the caterpillars. Scientists call these insects “plant bodyguards.”

Plants speak in a chemical vocabulary we can’t directly perceive or comprehend. The first important discoveries in plant communication were made in the lab in the nineteen-eighties, by isolating plants and their chemical emissions in Plexiglas chambers, but Rick Karban, the U.C. Davis ecologist, and others have set themselves the messier task of studying how plants exchange chemical signals outdoors, in a natural setting. Recently, I visited Karban’s study plot at the University of California’s Sagehen Creek Field Station, a few miles outside Truckee. On a sun-flooded hillside high in the Sierras, he introduced me to the ninety-nine sagebrush plants—low, slow-growing gray-green shrubs marked with plastic flags—that he and his colleagues have kept under close surveillance for more than a decade.

Karban, a fifty-nine-year-old former New Yorker, is slender, with a thatch of white curls barely contained by a floppy hat. He has shown that when sagebrush leaves are clipped in the spring—simulating an insect attack that triggers the release of volatile chemicals—both the clipped plant and its unclipped neighbors suffer significantly less insect damage over the season. Karban believes that the plant is alerting all its leaves to the presence of a pest, but its neighbors pick up the signal, too, and gird themselves against attack. “We think the sagebrush are basically eavesdropping on one another,” Karban said. He found that the more closely related the plants the more likely they are to respond to the chemical signal, suggesting that plants may display a form of kin recognition. Helping out your relatives is a good way to improve the odds that your genes will survive.

The field work and data collection that go into making these discoveries are painstaking in the extreme. At the bottom of a meadow raked by the slanted light of late summer, two collaborators from Japan, Kaori Shiojiri and Satomi Ishizaki, worked in the shade of a small pine, squatting over branches of sagebrush that Karban had tagged and cut. Using clickers, they counted every trident-shaped leaf on every branch, and then counted and recorded every instance of leaf damage, one column for insect bites, another for disease. At the top of the meadow, another collaborator, James Blande, a chemical ecologist from England, tied plastic bags around sagebrush stems and inflated the bags with filtered air. After waiting twenty minutes for the leaves to emit their volatiles, he pumped the air through a metal cylinder containing an absorbent material that collected the chemical emissions. At the lab, a gas chromatograph-mass spectrometer would yield a list of the compounds collected—more than a hundred in all. Blande offered to let me put my nose in one of the bags; the air was powerfully aromatic, with a scent closer to aftershave than to perfume. Gazing across the meadow of sagebrush, I found it difficult to imagine the invisible chemical chatter, including the calls of distress, going on all around—or that these motionless plants were engaged in any kind of “behavior” at all.

Research on plant communication may someday benefit farmers and their crops. Plant-distress chemicals could be used to prime plant defenses, reducing the need for pesticides. Jack Schultz, a chemical ecologist at the University of Missouri, who did some of the pioneering work on plant signalling in the early nineteen-eighties, is helping to develop a mechanical “nose” that, attached to a tractor and driven through a field, could help farmers identify plants under insect attack, allowing them to spray pesticides only when and where they are needed.

“This is where we practice our warning shots.”

Karban told me that, in the nineteen-eighties, people working on plant communication faced some of the same outrage that scientists working on plant intelligence (a term he cautiously accepts) do today. “This stuff has been enormously contentious,” he says, referring to the early days of research into plant communication, work that is now generally accepted. “It took me years to get some of these papers published. People would literally be screaming at one another at scientific meetings.” He added, “Plant scientists in general are incredibly conservative. We all think we want to hear novel ideas, but we don’t, not really.”

I first met Karban at a scientific meeting in Vancouver last July, when he presented a paper titled “Plant Communication and Kin Recognition in Sagebrush.” The meeting would have been the sixth gathering of the Society for Plant Neurobiology, if not for the fact that, under pressure from certain quarters of the scientific establishment, the group’s name had been changed four years earlier to the less provocative Society for Plant Signaling and Behavior. The plant biologist Elizabeth Van Volkenburgh, of the University of Washington, who was one of the founders of the society, told me that the name had been changed after a lively internal debate; she felt that jettisoning “neurobiology” was probably for the best. “I was told by someone at the National Science Foundation that the N.S.F. would never fund anything with the words ‘plant neurobiology’ in it. He said, and I quote, ‘ “Neuro” belongs to animals.’ ” (An N.S.F. spokesperson said that, while the society is not eligible for funding by the foundation’s neurobiology program, “the N.S.F. does not have a boycott of any sort against the society.”) Two of the society’s co-founders, Stefano Mancuso and František Baluška, argued strenuously against the name change, and continue to use the term “plant neurobiology” in their own work and in the names of their labs.

The meeting consisted of three days of PowerPoint presentations delivered in a large, modern lecture hall at the University of British Columbia before a hundred or so scientists. Most of the papers were highly technical presentations on plant signalling—the kind of incremental science that takes place comfortably within the confines of an established scientific paradigm, which plant signalling has become. But a handful of speakers presented work very much within the new paradigm of plant intelligence, and they elicited strong reactions.

The most controversial presentation was “Animal-Like Learning in Mimosa Pudica,” an unpublished paper by Monica Gagliano, a thirty-seven-year-old animal ecologist at the University of Western Australia who was working in Mancuso’s lab in Florence. Gagliano, who is tall, with long brown hair parted in the middle, based her experiment on a set of protocols commonly used to test learning in animals. She focussed on an elementary type of learning called “habituation,” in which an experimental subject is taught to ignore an irrelevant stimulus. “Habituation enables an organism to focus on the important information, while filtering out the rubbish,” Gagliano explained to the audience of plant scientists. How long does it take the animal to recognize that a stimulus is “rubbish,” and then how long will it remember what it has learned? Gagliano’s experimental question was bracing: Could the same thing be done with a plant?

Mimosa pudica , also called the “sensitive plant,” is that rare plant species with a behavior so speedy and visible that animals can observe it; the Venus flytrap is another. When the fernlike leaves of the mimosa are touched, they instantly fold up, presumably to frighten insects. The mimosa also collapses its leaves when the plant is dropped or jostled. Gagliano potted fifty-six mimosa plants and rigged a system to drop them from a height of fifteen centimetres every five seconds. Each “training session” involved sixty drops. She reported that some of the mimosas started to reopen their leaves after just four, five, or six drops, as if they had concluded that the stimulus could be safely ignored. “By the end, they were completely open,” Gagliano said to the audience. “They couldn’t care less anymore.”

Was it just fatigue? Apparently not: when the plants were shaken, they again closed up. “ ‘Oh, this is something new,’ ” Gagliano said, imagining these events from the plants’ point of view. “You see, you want to be attuned to something new coming in. Then we went back to the drops, and they didn’t respond.” Gagliano reported that she retested her plants after a week and found that they continued to disregard the drop stimulus, indicating that they “remembered” what they had learned. Even after twenty-eight days, the lesson had not been forgotten. She reminded her colleagues that, in similar experiments with bees, the insects forgot what they had learned after just forty-eight hours. Gagliano concluded by suggesting that “brains and neurons are a sophisticated solution but not a necessary requirement for learning,” and that there is “some unifying mechanism across living systems that can process information and learn.”

A lively exchange followed. Someone objected that dropping a plant was not a relevant trigger, since that doesn’t happen in nature. Gagliano pointed out that electric shock, an equally artificial trigger, is often used in animal-learning experiments. Another scientist suggested that perhaps her plants were not habituated, just tuckered out. She argued that twenty-eight days would be plenty of time to rebuild their energy reserves.

On my way out of the lecture hall, I bumped into Fred Sack, a prominent botanist at the University of British Columbia. I asked him what he thought of Gagliano’s presentation. “Bullshit,” he replied. He explained that the word “learning” implied a brain and should be reserved for animals: “Animals can exhibit learning, but plants evolve adaptations.” He was making a distinction between behavioral changes that occur within the lifetime of an organism and those which arise across generations. At lunch, I sat with a Russian scientist, who was equally dismissive. “It’s not learning,” he said. “So there’s nothing to discuss.”

“The forecast for today is grumpy.”

Later that afternoon, Gagliano seemed both stung by some of the reactions to her presentation and defiant. Adaptation is far too slow a process to explain the behavior she had observed, she told me. “How can they be adapted to something they have never experienced in their real world?” She noted that some of her plants learned faster than others, evidence that “this is not an innate or programmed response.” Many of the scientists in her audience were just getting used to the ideas of plant “behavior” and “memory” (terms that even Fred Sack said he was willing to accept); using words like “learning” and “intelligence” in plants struck them, in Sack’s words, as “inappropriate” and “just weird.” When I described the experiment to Lincoln Taiz, he suggested the words “habituation” or “desensitization” would be more appropriate than “learning.” Gagliano said that her mimosa paper had been rejected by ten journals: “None of the reviewers had problems with the data.” Instead, they balked at the language she used to describe the data. But she didn’t want to change it. “Unless we use the same language to describe the same behavior”—exhibited by plants and animals—“we can’t compare it,” she said.

Rick Karban consoled Gagliano after her talk. “I went through the same thing, just getting totally hammered,” he told her. “But you’re doing good work. The system is just not ready.” When I asked him what he thought of Gagliano’s paper, he said, “I don’t know if she’s got everything nailed down, but it’s a very cool idea that deserves to get out there and be discussed. I hope she doesn’t get discouraged.”

Scientists are often uncomfortable talking about the role of metaphor and imagination in their work, yet scientific progress often depends on both. “Metaphors help stimulate the investigative imagination of good scientists,” the British plant scientist Anthony Trewavas wrote in a spirited response to the Alpi letter denouncing plant neurobiology. “Plant neurobiology” is obviously a metaphor—plants don’t possess the type of excitable, communicative cells we call neurons. Yet the introduction of the term has raised a series of questions and inspired a set of experiments that promise to deepen our understanding not only of plants but potentially also of brains. If there are other ways of processing information, other kinds of cells and cell networks that can somehow give rise to intelligent behavior, then we may be more inclined to ask, with Mancuso, “What’s so special about neurons?”

Mancuso is the poet-philosopher of the movement, determined to win for plants the recognition they deserve and, perhaps, bring humans down a peg in the process. His somewhat grandly named International Laboratory of Plant Neurobiology, a few miles outside Florence, occupies a modest suite of labs and offices in a low-slung modern building. Here a handful of collaborators and graduate students work on the experiments Mancuso devises to test the intelligence of plants. Giving a tour of the labs, he showed me maize plants, grown under lights, that were being taught to ignore shadows; a poplar sapling hooked up to a galvanometer to measure its response to air pollution; and a chamber in which a PTR-TOF machine—an advanced kind of mass spectrometer—continuously read all the volatiles emitted by a succession of plants, from poplars and tobacco plants to peppers and olive trees. “We are making a dictionary of each species’ entire chemical vocabulary,” he explained. He estimates that a plant has three thousand chemicals in its vocabulary, while, he said with a smile, “the average student has only seven hundred words.”

Mancuso is fiercely devoted to plants—a scientist needs to “love” his subject in order to do it justice, he says. He is also gentle and unassuming, even when what he is saying is outrageous. In the corner of his office sits a forlorn Ficus benjamina, or weeping fig, and on the walls are photographs of Mancuso in an astronaut’s jumpsuit floating in the cabin of a zero-gravity aircraft; he has collaborated with the European Space Agency, which has supported his research on plant behavior in micro- and hyper-gravity. (One of his experiments was carried on board the last flight of the space shuttle Endeavor, in May of 2011.) A decade ago, Mancuso persuaded a Florentine bank foundation to underwrite much of his research and help launch the Society for Plant Neurobiology; his lab also receives grants from the European Union.

Early in our conversation, I asked Mancuso for his definition of “intelligence.” Spending so much time with the plant neurobiologists, I could feel my grasp on the word getting less sure. It turns out that I am not alone: philosophers and psychologists have been arguing over the definition of intelligence for at least a century, and whatever consensus there may once have been has been rapidly slipping away. Most definitions of intelligence fall into one of two categories. The first is worded so that intelligence requires a brain; the definition refers to intrinsic mental qualities such as reason, judgment, and abstract thought. The second category, less brain-bound and metaphysical, stresses behavior, defining intelligence as the ability to respond in optimal ways to the challenges presented by one’s environment and circumstances. Not surprisingly, the plant neurobiologists jump into this second camp.

“I define it very simply,” Mancuso said. “Intelligence is the ability to solve problems.” In place of a brain, “what I am looking for is a distributed sort of intelligence, as we see in the swarming of birds.” In a flock, each bird has only to follow a few simple rules, such as maintaining a prescribed distance from its neighbor, yet the collective effect of a great many birds executing a simple algorithm is a complex and supremely well-coördinated behavior. Mancuso’s hypothesis is that something similar is at work in plants, with their thousands of root tips playing the role of the individual birds—gathering and assessing data from the environment and responding in local but coördinated ways that benefit the entire organism.

“Neurons perhaps are overrated,” Mancuso said. “They’re really just excitable cells.” Plants have their own excitable cells, many of them in a region just behind the root tip. Here Mancuso and his frequent collaborator, František Baluška, have detected unusually high levels of electrical activity and oxygen consumption. They’ve hypothesized in a series of papers that this so-called “transition zone” may be the locus of the “root brain” first proposed by Darwin. The idea remains unproved and controversial. “What’s going on there is not well understood,” Lincoln Taiz told me, “but there is no evidence it is a command center.”

How plants do what they do without a brain—what Anthony Trewavas has called their “mindless mastery”—raises questions about how our brains do what they do. When I asked Mancuso about the function and location of memory in plants, he speculated about the possible role of calcium channels and other mechanisms, but then he reminded me that mystery still surrounds where and how our memories are stored: “It could be the same kind of machinery, and figuring it out in plants may help us figure it out in humans.”

“Theres so much evidence we should put some aside for a different case.”

The hypothesis that intelligent behavior in plants may be an emergent property of cells exchanging signals in a network might sound far-fetched, yet the way that intelligence emerges from a network of neurons may not be very different. Most neuroscientists would agree that, while brains considered as a whole function as centralized command centers for most animals, within the brain there doesn’t appear to be any command post; rather, one finds a leaderless network. That sense we get when we think about what might govern a plant—that there is no there there, no wizard behind the curtain pulling the levers—may apply equally well to our brains.

In Martin Amis’s 1995 novel, “The Information,” we meet a character who aspires to write “The History of Increasing Humiliation,” a treatise chronicling the gradual dethronement of humankind from its position at the center of the universe, beginning with Copernicus. “Every century we get smaller,” Amis writes. Next came Darwin, who brought the humbling news that we are the product of the same natural laws that created animals. In the last century, the formerly sharp lines separating humans from animals—our monopolies on language, reason, toolmaking, culture, even self-consciousness—have been blurred, one after another, as science has granted these capabilities to other animals.

Mancuso and his colleagues are writing the next chapter in “The History of Increasing Humiliation.” Their project entails breaking down the walls between the kingdoms of plants and animals, and it is proceeding not only experiment by experiment but also word by word. Start with that slippery word “intelligence.” Particularly when there is no dominant definition (and when measurements of intelligence, such as I.Q., have been shown to be culturally biased), it is possible to define intelligence in a way that either reinforces the boundary between animals and plants (say, one that entails abstract thought) or undermines it. Plant neurobiologists have chosen to define intelligence democratically, as an ability to solve problems or, more precisely, to respond adaptively to circumstances, including ones unforeseen in the genome.

“I agree that humans are special,” Mancuso says. “We are the first species able to argue about what intelligence is. But it’s the quantity, not the quality” of intelligence that sets us apart. We exist on a continuum with the acacia, the radish, and the bacterium. “Intelligence is a property of life,” he says. I asked him why he thinks people have an easier time granting intelligence to computers than to plants. (Fred Sack told me that he can abide the term “artificial intelligence,” because the intelligence in this case is modified by the word “artificial,” but not “plant intelligence.” He offered no argument, except to say, “I’m in the majority in saying it’s a little weird.”) Mancuso thinks we’re willing to accept artificial intelligence because computers are our creations, and so reflect our own intelligence back at us. They are also our dependents, unlike plants: “If we were to vanish tomorrow, the plants would be fine, but if the plants vanished . . .” Our dependence on plants breeds a contempt for them, Mancuso believes. In his somewhat topsy-turvy view, plants “remind us of our weakness.”

“Memory” may be an even thornier word to apply across kingdoms, perhaps because we know so little about how it works. We tend to think of memories as immaterial, but in animal brains some forms of memory involve the laying down of new connections in a network of neurons. Yet there are ways to store information biologically that don’t require neurons. Immune cells “remember” their experience of pathogens, and call on that memory in subsequent encounters. In plants, it has long been known that experiences such as stress can alter the molecular wrapping around the chromosomes; this, in turn, determines which genes will be silenced and which expressed. This so-called “epigenetic” effect can persist and sometimes be passed down to offspring. More recently, scientists have found that life events such as trauma or starvation produce epigenetic changes in animal brains (coding for high levels of cortisol, for example) that are long-lasting and can also be passed down to offspring, a form of memory much like that observed in plants.

While talking with Mancuso, I kept thinking about words like “will,” “choice,” and “intention,” which he seemed to attribute to plants rather casually, almost as if they were acting consciously. At one point, he told me about the dodder vine, Cuscuta europaea , a parasitic white vine that winds itself around the stalk of another plant and sucks nourishment from it. A dodder vine will “choose” among several potential hosts, assessing, by scent, which offers the best potential nourishment. Having selected a target, the vine then performs a kind of cost-benefit calculation before deciding exactly how many coils it should invest—the more nutrients in the victim, the more coils it deploys. I asked Mancuso whether he was being literal or metaphorical in attributing intention to plants.

“Here, I’ll show you something,” he said. “Then you tell me if plants have intention.” He swivelled his computer monitor around and clicked open a video.

Time-lapse photography is perhaps the best tool we have to bridge the chasm between the time scale at which plants live and our own. This example was of a young bean plant, shot in the lab over two days, one frame every ten minutes. A metal pole on a dolly stands a couple of feet away. The bean plant is “looking” for something to climb. Each spring, I witness the same process in my garden, in real time. I always assumed that the bean plants simply grow this way or that, until they eventually bump into something suitable to climb. But Mancuso’s video seems to show that this bean plant “knows” exactly where the metal pole is long before it makes contact with it. Mancuso speculates that the plant could be employing a form of echolocation. There is some evidence that plants make low clicking sounds as their cells elongate; it’s possible that they can sense the reflection of those sound waves bouncing off the metal pole.

The bean plant wastes no time or energy “looking”—that is, growing—anywhere but in the direction of the pole. And it is striving (there is no other word for it) to get there: reaching, stretching, throwing itself over and over like a fly rod, extending itself a few more inches with every cast, as it attempts to wrap its curling tip around the pole. As soon as contact is made, the plant appears to relax; its clenched leaves begin to flutter mildly. All this may be nothing more than an illusion of time-lapse photography. Yet to watch the video is to feel, momentarily, like one of the aliens in Mancuso’s formative science-fiction story, shown a window onto a dimension of time in which these formerly inert beings come astonishingly to life, seemingly conscious individuals with intentions.

The Intelligent Plant

In October, I loaded the bean video onto my laptop and drove down to Santa Cruz to play it for Lincoln Taiz. He began by questioning its value as scientific data: “Maybe he has ten other videos where the bean didn’t do that. You can’t take one interesting variation and generalize from it.” The bean’s behavior was, in other words, an anecdote, not a phenomenon. Taiz also pointed out that the bean in the video was leaning toward the pole in the first frame. Mancuso then sent me another video with two perfectly upright bean plants that exhibited very similar behavior. Taiz was now intrigued. “If he sees that effect consistently, it would be exciting,” he said—but it would not necessarily be evidence of plant intention. “If the phenomenon is real, it would be classified as a tropism,” such as the mechanism that causes plants to bend toward light. In this case, the stimulus remains unknown, but tropisms “do not require one to postulate either intentionality or ‘brainlike’ conceptualization,” Taiz said. “The burden of proof for the latter interpretation would clearly be on Stefano.”

Perhaps the most troublesome and troubling word of all in thinking about plants is “consciousness.” If consciousness is defined as inward awareness of oneself experiencing reality—“the feeling of what happens,” in the words of the neuroscientist Antonio Damasio—then we can (probably) safely conclude that plants don’t possess it. But if we define the term simply as the state of being awake and aware of one’s environment—“online,” as the neuroscientists say—then plants may qualify as conscious beings, at least according to Mancuso and Baluška. “The bean knows exactly what is in the environment around it,” Mancuso said. “We don’t know how. But this is one of the features of consciousness: You know your position in the world. A stone does not.”

In support of their contention that plants are conscious of their environment, Mancuso and Baluška point out that plants can be rendered unconscious by the same anesthetics that put animals out: drugs can induce in plants an unresponsive state resembling sleep. (A snoozing Venus flytrap won’t notice an insect crossing its threshold.) What’s more, when plants are injured or stressed, they produce a chemical—ethylene—that works as an anesthetic on animals. When I learned this startling fact from Baluška in Vancouver, I asked him, gingerly, if he meant to suggest that plants could feel pain. Baluška, who has a gruff mien and a large bullet-shaped head, raised one eyebrow and shot me a look that I took to mean he deemed my question impertinent or absurd. But apparently not.

“If plants are conscious, then, yes, they should feel pain,” he said. “If you don’t feel pain, you ignore danger and you don’t survive. Pain is adaptive.” I must have shown some alarm. “That’s a scary idea,” he acknowledged with a shrug. “We live in a world where we must eat other organisms.”

Unprepared to consider the ethical implications of plant intelligence, I could feel my resistance to the whole idea stiffen. Descartes, who believed that only humans possessed self-consciousness, was unable to credit the idea that other animals could suffer from pain. So he dismissed their screams and howls as mere reflexes, as meaningless physiological noise. Could it be remotely possible that we are now making the same mistake with plants? That the perfume of jasmine or basil, or the scent of freshly mowed grass, so sweet to us, is (as the ecologist Jack Schultz likes to say) the chemical equivalent of a scream? Or have we, merely by posing such a question, fallen back into the muddied waters of “The Secret Life of Plants”?

Lincoln Taiz has little patience for the notion of plant pain, questioning what, in the absence of a brain, would be doing the feeling. He puts it succinctly: “No brain, no pain.” Mancuso is more circumspect. We can never determine with certainty whether plants feel pain or whether their perception of injury is sufficiently like that of animals to be called by the same word. (He and Baluška are careful to write of “plant-specific pain perception.”) “We just don’t know, so we must be silent.”

Mancuso believes that, because plants are sensitive and intelligent beings, we are obliged to treat them with some degree of respect. That means protecting their habitats from destruction and avoiding practices such as genetic manipulation, growing plants in monocultures, and training them in bonsai. But it does not prevent us from eating them. “Plants evolved to be eaten—it is part of their evolutionary strategy,” he said. He cited their modular structure and lack of irreplaceable organs in support of this view.

The central issue dividing the plant neurobiologists from their critics would appear to be this: Do capabilities such as intelligence, pain perception, learning, and memory require the existence of a brain, as the critics contend, or can they be detached from their neurobiological moorings? The question is as much philosophical as it is scientific, since the answer depends on how these terms get defined. The proponents of plant intelligence argue that the traditional definitions of these terms are anthropocentric—a clever reply to the charges of anthropomorphism frequently thrown at them. Their attempt to broaden these definitions is made easier by the fact that the meanings of so many of these terms are up for grabs. At the same time, since these words were originally created to describe animal attributes, we shouldn’t be surprised at the awkward fit with plants. It seems likely that, if the plant neurobiologists were willing to add the prefix “plant-specific” to intelligence and learning and memory and consciousness (as Mancuso and Baluška are prepared to do in the case of pain), then at least some of this “scientific controversy” might evaporate.

Indeed, I found more consensus on the underlying science than I expected. Even Clifford Slayman, the Yale biologist who signed the 2007 letter dismissing plant neurobiology, is willing to acknowledge that, although he doesn’t think plants possess intelligence, he does believe they are capable of “intelligent behavior,” in the same way that bees and ants are. In an e-mail exchange, Slayman made a point of underlining this distinction: “We do not know what constitutes intelligence, only what we can observe and judge as intelligent behavior.” He defined “intelligent behavior” as “the ability to adapt to changing circumstances” and noted that it “must always be measured relative to a particular environment.” Humans may or may not be intrinsically more intelligent than cats, he wrote, but when a cat is confronted with a mouse its behavior is likely to be demonstrably more intelligent.

“Those who ignore history are entitled to repeat it.”

Slayman went on to acknowledge that “intelligent behavior could perfectly well develop without such a nerve center or headquarters or director or brain—whatever you want to call it. Instead of ‘brain,’ think ‘network.’ It seems to be that many higher organisms are internally networked in such a way that local changes,” such as the way that roots respond to a water gradient, “cause very local responses which benefit the entire organism.” Seen that way, he added, the outlook of Mancuso and Trewavas is “pretty much in line with my understanding of biochemical/biological networks.” He pointed out that while it is an understandable human prejudice to favor the “nerve center” model, we also have a second, autonomic nervous system governing our digestive processes, which “operates most of the time without instructions from higher up.” Brains are just one of nature’s ways of getting complex jobs done, for dealing intelligently with the challenges presented by the environment. But they are not the only way: “Yes, I would argue that intelligent behavior is a property of life.”

To define certain words in such a way as to bring plants and animals beneath the same semantic umbrella—whether of intelligence or intention or learning—is a philosophical choice with important consequences for how we see ourselves in nature. Since “The Origin of Species,” we have understood, at least intellectually, the continuities among life’s kingdoms—that we are all cut from the same fabric of nature. Yet our big brains, and perhaps our experience of inwardness, allow us to feel that we must be fundamentally different—suspended above nature and other species as if by some metaphysical “skyhook,” to borrow a phrase from the philosopher Daniel Dennett. Plant neurobiologists are intent on taking away our skyhook, completing the revolution that Darwin started but which remains—psychologically, at least—incomplete.

“What we learned from Darwin is that competence precedes comprehension,” Dennett said when I called to talk to him about plant neurobiology. Upon a foundation of the simplest competences—such as the on-off switch in a computer, or the electrical and chemical signalling of a cell—can be built higher and higher competences until you wind up with something that looks very much like intelligence. “The idea that there is a bright line, with real comprehension and real minds on the far side of the chasm, and animals or plants on the other—that’s an archaic myth.” To say that higher competences such as intelligence, learning, and memory “mean nothing in the absence of brains” is, in Dennett’s view, “cerebrocentric.”

All species face the same existential challenges—obtaining food, defending themselves, reproducing—but under wildly varying circumstances, and so they have evolved wildly different tools in order to survive. Brains come in handy for creatures that move around a lot; but they’re a disadvantage for ones that are rooted in place. Impressive as it is to us, self-consciousness is just another tool for living, good for some jobs, unhelpful for others. That humans would rate this particular adaptation so highly is not surprising, since it has been the shining destination of our long evolutionary journey, along with the epiphenomenon of self-consciousness that we call “free will.”

In addition to being a plant physiologist, Lincoln Taiz writes about the history of science. “Starting with Darwin’s grandfather, Erasmus,” he told me, “there has been a strain of teleology in the study of plant biology”—a habit of ascribing purpose or intention to the behavior of plants. I asked Taiz about the question of “choice,” or decision-making, in plants, as when they must decide between two conflicting environmental signals—water and gravity, for example.

“Does the plant decide in the same way that we choose at a deli between a Reuben sandwich or lox and bagel?” Taiz asked. “No, the plant response is based entirely on the net flow of auxin and other chemical signals. The verb ‘decide’ is inappropriate in a plant context. It implies free will. Of course, one could argue that humans lack free will too, but that is a separate issue.”

I asked Mancuso if he thought that a plant decides in the same way we might choose at a deli between a Reuben or lox and bagels.

“Yes, in the same way,” Mancuso wrote back, though he indicated that he had no idea what a Reuben was. “Just put ammonium nitrate in the place of Reuben sandwich (whatever it is) and phosphate instead of salmon, and the roots will make a decision.” But isn’t the root responding simply to the net flow of certain chemicals? “I’m afraid our brain makes decisions in the same exact way.”

“Why would a plant care about Mozart?” the late ethnobotanist Tim Plowman would reply when asked about the wonders catalogued in “The Secret Life of Plants.” “And even if it did, why should that impress us? They can eat light, isn’t that enough?”

One way to exalt plants is by demonstrating their animal-like capabilities. But another way is to focus on all the things plants can do that we cannot. Some scientists working on plant intelligence have questioned whether the “animal-centric” emphasis, along with the obsession with the term “neurobiology,” has been a mistake and possibly an insult to the plants. “I have no interest in making plants into little animals,” one scientist wrote during the dustup over what to call the society. “Plants are unique,” another wrote. “There is no reason to . . . call them demi-animals.”

When I met Mancuso for dinner during the conference in Vancouver, he sounded very much like a plant scientist getting over a case of “brain envy”—what Taiz had suggested was motivating the plant neurologists. If we could begin to understand plants on their own terms, he said, “it would be like being in contact with an alien culture. But we could have all the advantages of that contact without any of the problems—because it doesn’t want to destroy us!” How do plants do all the amazing things they do without brains? Without locomotion? By focussing on the otherness of plants rather than on their likeness, Mancuso suggested, we stand to learn valuable things and develop important new technologies. This was to be the theme of his presentation to the conference, the following morning, on what he called “bioinspiration.” How might the example of plant intelligence help us design better computers, or robots, or networks?

Mancuso was about to begin a collaboration with a prominent computer scientist to design a plant-based computer, modelled on the distributed computing performed by thousands of roots processing a vast number of environmental variables. His collaborator, Andrew Adamatzky, the director of the International Center of Unconventional Computing, at the University of the West of England, has worked extensively with slime molds, harnessing their maze-navigating and computational abilities. (Adamatzky’s slime molds, which are a kind of amoeba, grow in the direction of multiple food sources simultaneously, usually oat flakes, in the process computing and remembering the shortest distance between any two of them; he has used these organisms to model transportation networks.) In an e-mail, Adamatzky said that, as a substrate for biological computing, plants offered both advantages and disadvantages over slime molds. “Plants are more robust,” he wrote, and “can keep their shape for a very long time,” although they are slower-growing and lack the flexibility of slime molds. But because plants are already “analog electrical computers,” trafficking in electrical inputs and outputs, he is hopeful that he and Mancuso will be able to harness them for computational tasks.

“You havent seen security till youve seen it on the iPad 2.”

Mancuso was also working with Barbara Mazzolai, a biologist-turned-engineer at the Italian Institute of Technology, in Genoa, to design what he called a “plantoid”: a robot designed on plant principles. “If you look at the history of robots, they are always based on animals—they are humanoids or insectoids. If you want something swimming, you look at a fish. But what about imitating plants instead? What would that allow you to do? Explore the soil!” With a grant from the European Union’s Future and Emerging Technologies program, their team is developing a “robotic root” that, using plastics that can elongate and then harden, will be able to slowly penetrate the soil, sense conditions, and alter its trajectory accordingly. “If you want to explore other planets, the best thing is to send plantoids.”

The most bracing part of Mancuso’s talk on bioinspiration came when he discussed underground plant networks. Citing the research of Suzanne Simard, a forest ecologist at the University of British Columbia, and her colleagues, Mancuso showed a slide depicting how trees in a forest organize themselves into far-flung networks, using the underground web of mycorrhizal fungi which connects their roots to exchange information and even goods. This “wood-wide web,” as the title of one paper put it, allows scores of trees in a forest to convey warnings of insect attacks, and also to deliver carbon, nitrogen, and water to trees in need.

When I reached Simard by phone, she described how she and her colleagues track the flow of nutrients and chemical signals through this invisible underground network. They injected fir trees with radioactive carbon isotopes, then followed the spread of the isotopes through the forest community using a variety of sensing methods, including a Geiger counter. Within a few days, stores of radioactive carbon had been routed from tree to tree. Every tree in a plot thirty metres square was connected to the network; the oldest trees functioned as hubs, some with as many as forty-seven connections. The diagram of the forest network resembled an airline route map.

The pattern of nutrient traffic showed how “mother trees” were using the network to nourish shaded seedlings, including their offspring—which the trees can apparently recognize as kin—until they’re tall enough to reach the light. And, in a striking example of interspecies coöperation, Simard found that fir trees were using the fungal web to trade nutrients with paper-bark birch trees over the course of the season. The evergreen species will tide over the deciduous one when it has sugars to spare, and then call in the debt later in the season. For the forest community, the value of this coöperative underground economy appears to be better over-all health, more total photosynthesis, and greater resilience in the face of disturbance.

In his talk, Mancuso juxtaposed a slide of the nodes and links in one of these subterranean forest networks with a diagram of the Internet, and suggested that in some respects the former was superior. “Plants are able to create scalable networks of self-maintaining, self-operating, and self-repairing units,” he said. “Plants.”

As I listened to Mancuso limn the marvels unfolding beneath our feet, it occurred to me that plants do have a secret life, and it is even stranger and more wonderful than the one described by Tompkins and Bird. When most of us think of plants, to the extent that we think about plants at all, we think of them as old—holdovers from a simpler, prehuman evolutionary past. But for Mancuso plants hold the key to a future that will be organized around systems and technologies that are networked, decentralized, modular, reiterated, redundant—and green, able to nourish themselves on light. “Plants are the great symbol of modernity.” Or should be: their brainlessness turns out to be their strength, and perhaps the most valuable inspiration we can take from them.

At dinner in Vancouver, Mancuso said, “Since you visited me in Florence, I came across this sentence of Karl Marx, and I became obsessed with it: ‘Everything that is solid melts into air.’ Whenever we build anything, it is inspired by the architecture of our bodies. So it will have a solid structure and a center, but that is inherently fragile. This is the meaning of that sentence—‘Everything solid melts into air.’ So that’s the question: Can we now imagine something completely different, something inspired instead by plants?” ♦

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Plants can communicate and respond to touch. does that mean they're intelligent.

"The primary way plants communicate with each other is through a language, so to speak, of chemical gasses," journalist Zoë Schlanger says.

In the 1960s and '70s, a series of questionable experiments claimed to prove that plants could behave like humans, that they had feelings, responded to music and could even take a polygraph test .

Though most of those claims have since been debunked, climate journalist Zoë Schlanger says a new wave of research suggests that plants are indeed "intelligent" in complex ways that challenge our understanding of agency and consciousness.

"Agency is this effect of having ... an active stake in the outcome of your life," Schlanger says. "And when I was looking at plants and speaking to botanists, it became very clear to me that plants have this."

In her new book, The Light Eaters: How the Unseen World of Plant Intelligence Offers a New Understanding of Life on Earth , Schlanger, a staff reporter at The Atlantic, writes about how plants use information from the environment, and from the past, to make "choices" for the future.

Schlanger notes that some tomato plants, when being eaten by caterpillars, fill their leaves with a chemical that makes them so unappetizing that the caterpillars start eating each other instead. Corn plants have been known to sample the saliva of predator caterpillars — and then use that information to emit a chemical to attract a parasitic wasp that will attack the caterpillar.

Schlanger acknowledges that our understanding of plants is still developing — as are the definitions of "intelligence" and "consciousness." "Science is there [for] observation and to experiment, but it can't answer questions about this ineffable, squishy concept of intelligence and consciousness," she says.

But, she adds, "part of me feels like it almost doesn't matter, because what we see plants doing — what we now understand they can do — simply brings them into this realm of alert, active processing beings, which is a huge step from how many of us were raised to view them, which is more like ornaments in our world or this decorative backdrop for our our lives."

Interview highlights

research on plants feeling pain

On the concept of plant "intelligence"

Intelligence is this thing that's loaded with so much human meaning. It's too muddled up sometimes with academic notions of intelligence. ... Is this even something we want to layer on to plants? And that's something that I hear a lot of plant scientists talk about. They recognize more than anyone that plants are not little humans. They don't want their subjects to be reduced in a way to human tropes or human standards of either of those things.

On the debate over if plants have nervous systems

I was able to go to a lab in Wisconsin where there [were] plants that had ... been engineered to glow, but only to glow when they've been touched. So I used tweezers to pinch a plant on its vein, ... the kind of mid-rib of a leaf. And I got to watch this glowing green signal emanate from the point where I pinch the plant out to the whole rest of the plant. Within two minutes, the whole plant had received a signal of my touch, of my "assault," so to speak, with these tweezers. And research like that is leading people within the plant sciences, but also people who work on neurobiology in people to question whether or not it's time to expand the notion of a nervous system.

On if plants feel pain

We have nothing at the moment to suggest that plants feel pain, but do they sense being touched, or sense being eaten, and respond with a flurry of defensive chemicals that suggest that they really want to prevent whatever's going on from continuing? Absolutely. So this is where we get into tricky territory. Do we ascribe human concepts like pain ... to a plant, even though it has no brain? And we can't ask it if it feels pain. We have not found pain receptors in a plant. But then again, I mean, the devil's advocate view here is that we only found the mechanoreceptors for pain in humans, like, fairly recently. But we do know plants are receiving inputs all the time. They know when a caterpillar is chewing on them, and they will respond with aggressive defensiveness. They will do wild things to keep that caterpillar from destroying them further.

On how plants communicate with each other

Zoë Schlanger is a staff writer at <em>The Atlantic.</em>

The primary way plants communicate with each other is through a language, so to speak, of chemical gasses. ... And there's little pores on plants that are microscopic. And under the microscope, they look like little fish lips. ... And they open to release these gasses. And those gasses contain information. So when a plant is being eaten or knocked over by an animal or hit by wind too hard, it will release an alarm call that other plants in the area can pick up on. And this alarm call can travel pretty long distances, and the plants that receive it will prime their immune systems and their defense systems to be ready for this invasion, for this group of chewing animals before they even arrive. So it's a way of saving themselves, and it makes evolutionary sense. If you're a plant, you don't want to be standing out in a field alone, so to speak. It's not good for reproductive fitness. It's not good for attracting pollinators. It's often in the interest of plants to warn their neighbors of attacks like this.

On plant "memory"

There's one concept that I think is very beautiful, called the "memory of winter." And that's this thing where many plants, most of our fruit trees, for example, have to have the "memory," so to speak, of a certain number of days of cold in the winter in order to bloom in the spring. It's not enough that the warm weather comes. They have to get this profound cold period as well, which means to some extent they're counting. They're counting the elapsed days of cold and then the elapsed days of warmth to make sure they're also not necessarily emerging in a freak warm spell in February. This does sometimes happen, of course. We hear stories about farmers losing their crops to freak warm spells. But there is evidence to suggest there's parts of plants physiology that helps them record this information. But much like in people, we don't quite know the substrate of that memory. We can't quite locate where or how it's possibly being recorded.

On not anthropomorphizing plants

What's interesting is that scientists and botany journals will do somersaults to avoid using human language for plants. And I totally get why. But when you go meet them in their labs, they are willing to anthropomorphize the heck out of their study subjects. They'll say things like, "Oh, the plants hate when I do that." Or, "They really like this when I do this or they like this treatment." I once heard a scientist talk about, "We're going to go torture the plant again." So they're perfectly willing to do that in private. And the reason for that is not because they're holding some secret about how plants are actually just little humans. It's that they've already resolved that complexity in their mind. They trust themselves to not be reducing their subjects to human, simplistic human tropes. And that's going to be a task for all of us to somehow come to that place.

It's a real challenge for me. So much of what I was learning while doing research for this book was super intangible. You can't see a plant communicating, you can't watch a plant priming its immune system or manipulating an insect. A lot of these things are happening in invisible ways. ... Now when I go into a park, I feel totally surrounded by little aliens. I know that there is immense plant drama happening all over the place around me.

Sam Briger and Susan Nyakundi produced and edited this interview for broadcast. Bridget Bentz and Molly Seavy-Nesper adapted it for the web.

Copyright 2024 Fresh Air

research on plants feeling pain

June 5, 2012

Do Plants Think?

Scientist Daniel Chamovitz unveils the surprising world of plants that see, feel, smell—and remember

By Gareth Cook

How aware are plants? This is the central question behind a fascinating new book, “ What a Plant Knows, ” by Daniel Chamovitz , director of the Manna Center for Plant Biosciences at Tel Aviv University. A plant, he argues, can see, smell and feel. It can mount a defense when under siege, and warn its neighbors of trouble on the way. A plant can even be said to have a memory. But does this mean that plants think — or that one can speak of a “neuroscience” of the flower? Chamovitz answered questions from Mind Matters editor Gareth Cook .

1. How did you first get interested in this topic? My interest in the parallels between plant and human senses got their start when I was a young postdoctoral fellow in the laboratory of Xing-Wang Deng at Yale University in the mid 1990s. I was interested in studying a biological process that would be specific to plants, and would not be connected to human biology (probably as a response to the six other “doctors” in my family, all of whom are physicians). So I was drawn to the question of how plants sense light to regulate their development.

It had been known for decades that plants use light not only for photosynthesis, but also as a signal that changes the way plants grow. In my research I discovered a unique group of genes necessary for a plant to determine if it’s in the light or in the dark. When we reported our findings, it appeared these genes were unique to the plant kingdom, which fit well with my desire to avoid any thing touching on human biology. But much to my surprise and against all of my plans, I later discovered that this same group of genes is also part of the human DNA.

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This led to the obvious question as to what these seemingly “plant-specific” genes do in people.  Many years later, we now know that these same genes are important in animals for the timing of cell division, the axonal growth of neurons, and the proper functioning of the immune system.

But most amazingly, these genes also regulate responses to light in animals! While we don’t change our form in response to light as plants do, we are affected by lab at the level of our internal clock. Our internal circadian clocks keep us on a 24 hour rhythm, which is why when we travel half way around the world we experience jet lag. But this clock can be reset by light. A few years ago I showed, in collaboration with Justin Blau at NYU, that mutant fruit flies that were missing some of these genes lost the ability to respond to light. In other words, if we changed their clocks, they remained in jetlag.

This led me to realize that the genetic difference between plants and animals is not as significant as I had once naively believed. So while not actively researching this field, I began to question the parallels between plant and human biology even as my own research evolved from studying plant responses to light to leukemia in fruit flies.

2. How do think people should change how they think about plants? People have to realize that plants are complex organisms that live rich, sensual lives. You know many of us relate to plants as inanimate objects, not much different from stones. Even the fact that many people substitute silk flowers for real ones, or artificial Christmas trees for a live one, is exemplary at some level of how we relate to plants. You know, I don’t know anyone who keeps a stuffed dog in place of a real one!

But if we realize that all of plant biology arises from the evolutionary constriction of the “rootedness” that keep plants immobile, then we can start to appreciate the very sophisticated biology going on in leaves and flowers. If you think about it, rootedness is a huge evolutionary constraint. It means that plants can’t escape a bad environment, can’t migrate in the search of food or a mate. So plants had to develop incredibly sensitive and complex sensory mechanisms that would let them survive in ever changing environments. I mean if you’re hungry or thirsty, you can walk to the nearest watering hole (or bar). If you’re hot, you can move north, if you’re looking for a mate, you can go out to a party. But plants are immobile. They need to see where their food is. They need to feel the weather, and they need to smell danger. And then they need to be able to integrate all of this very dynamic and changing information. Just because we don’t see plants moving doesn’t mean that there’s not a very rich and dynamic world going on inside the plant.

3. You say that plants have a sense of smell? Sure. But to answer this we have to define for ourselves what “smell” is. When we smell something, we sense a volatile chemical that’s dissolved in the air, and then react in someway to this smell. The clearest example in plants is what happens during fruit ripening. You may have heard that if you put a ripe and an unripe fruit together in the same bag, the unripe one will ripen faster. This happens because the ripe one releases a ripening pheromone into the air, and the green fruit smells it and then starts ripening itself. This happens not only in our kitchens, but also, or even primarily, in nature. When one fruit starts to ripen, it releases this hormone which is called ethylene, which is sensed by neighboring fruits, until entire trees and groves ripen more or less in synchrony.

Another example of a plant using smell is how a parasitic plant called dodder finds its food. Dodder can’t do photosynthesis, and so has to live off of other plants. The way it finds its host plant is by smelling. A dodder can detect minute amounts of chemicals released in the air by neighboring plants, and will actually pick the one that it finds tastiest! In one classic experiment scientists showed that dodder prefers tomato to wheat because it prefers the smell.

3B. How about hearing? This is a bit trickier because while loads of research support the idea that plants see, smell, taste and feel, support for plant auditory prowess is indirectly proportional to the amount of anecdotal information we have about the ways in which music may influence how a plant grows. Many of us have heard stories about plants flourishing in rooms with classical music. Typically, though, much of the research on music and plants was, to put it mildly, not carried out by investigators grounded in the scientific method. Not surprisingly, in most of these studies, the plants thrived in music that the experimenter also preferred.

From an evolutionary perspective, it also could be that plants haven’t really needed to hear. The evolutionary advantage created from hearing in humans and other animals serves as one way our bodies warn us of potentially dangerous situations. Our early human ancestors could hear a dangerous predator stalking them through the forest, while today we hear the motor of an approaching car. Hearing also enables rapid communication between individuals and between animals. Elephants can find each other across vast distances by vocalizing subsonic waves that rumble around objects and travel for miles. A dolphin pod can find a dolphin pup lost in the ocean through its distress chirps. What’s common in all of these situations is that sound enables a rapid communication of information and a response, which is often movement—fleeing from a fire, escaping from attack, finding family.

But plants are rooted, sessile organisms. While they can grow toward the sun, and bend with gravity, they can’t flee. They can’t escape. They don’t migrate with the seasons. As such, perhaps the audible signals we’re used to in our world are irrelevant for a plant.

All that being said, I have to cover myself hear by pointing out that some very recent research hints that plants may respond to sounds. Not to music mind you, which is irrelevant for a plant, but to certain vibrations. It will be very interesting to see how this pans out.

4. Do plants communicate with each other? At a basic level, yes.  But I guess it centers around how you define communication. There is no doubt that plants respond to cues from other plants. For example, if a maple tree is attacked by bugs, it releases a pheromone into the air that is picked up by the neighboring trees. This induces the receiving trees to start making chemicals that will help it fight off the impending bug attack. So on the face of it, this is definitely communication.

But I think we also have to ask the question of intent (if we can even use that word when describing plants, but humor me while I anthropomorphize). Are the trees communicating, meaning is that attacked tree warning its surrounding ones? Or could it be more subtle? Maybe it makes more sense that the attacked branch is communicating to the other branches of the same tree in an effort for self survival, while the neighboring trees, well they’re just eavesdropping and benefiting from the signal.

There are also other examples of this type of communication. For example a very recent study showed that plants also communicate through signals passed from root to root. In this case the “talking” plant had been stressed by drought, and it “told” its neighboring plants to prepare for a lack of water. We know the signal went through the roots because this never happened if the two plants were simply in neighboring pots. They had to have neighboring roots.

5. Do plants have a memory? Plants definitely have several different forms of memory, just like people do. They have short term memory, immune memory and even transgenerational memory! I know this is a hard concept to grasp for some people, but if memory entails forming the memory (encoding information), retaining the memory (storing information), and recalling the memory (retrieving information), then plants definitely remember. For example a Venus Fly Trap needs to have two of the hairs on its leaves touched by a bug in order to shut, so it remembers that the first one has been touched. But this only lasts about 20 seconds, and then it forgets. Wheat seedlings remember that they’ve gone through winter before they start to flower and make seeds. And some stressed plants give rise to progeny that are more resistant to the same stress, a type of transgenerational memory that’s also been recently shown also in animals. While the short term memory in the venus fly trap is electricity-based, much like neural activity, the longer term memories are based in epigenetics — changes in gene activity that don’t require alterations in the DNA code, as mutations do, which are still passed down from parent to offspring. 

6. Would you say, then, that plants “think”? No I wouldn’t, but maybe that’s where I’m still limited in my own thinking! To me thinking and information processing are two different constructs. I have to be careful here since this is really bordering on the philosophical, but I think purposeful thinking necessitates a highly developed brain and autonoetic , or at least noetic, consciousness. Plants exhibit elements of anoetic consciousness which doesn’t include, in my understanding, the ability to think.  Just as a plant can’t suffer subjective pain in the absence of a brain, I also don’t think that it thinks.

7. Do you see any analogy between what plants do and what the human brain does? Can there be a neuroscience of plants, minus the neurons? First off, and at the risk of offending some of my closest friends, I think the term plant neurobiology is as ridiculous as say, human floral biology. Plants do not have neuron just as humans don’t have flowers!

But you don’t need neurons in order to have cell to cell communication and information storage and processing.  Even in animals, not all information is processed or stored only in the brain. The brain is dominant in higher-order processing in more complex animals, but not in simple ones.  Different parts of the plant communicate with each other, exchanging information on cellular, physiological and environmental states. For example root growth is dependent on a hormonal signal that’s generated in the tips of shoots and transported to the growing roots, while shoot development is partially dependent on a signal that’s generated in the roots. Leaves send signals to the tip of the shoot telling them to start making flowers.  In this way, if you really want to do some major hand waving, the entire plant is analogous to the brain.

But while plants don’t have neurons, plants both produce and are affected by neuroactive chemicals! For example, the glutamate receptor is a neuroreceptor in the human brain necessary for memory formation and learning. While plants don’t have neurons, they do have glutamate receptors and what’s fascinating is that the same drugs that inhibit the human glutamate receptor also affect plants. From studying these proteins in plants, scientists have learned how glutamate receptors mediate communication from cell to cell. So maybe the question should be posed to a neurobiologist if there could be a botany of humans, minus the flowers!

Darwin, one of the great plant researchers, proposed what has become known as the “root-brain” hypothesis. Darwin proposed that the tip of the root, the part that we call the meristem, acts like the brain does in lower animals, receiving sensory input and directing movement. Several modern-day research groups are following up on this line of research.

Are you a scientist who specializes in neuroscience, cognitive science, or psychology? And have you read a recent peer-reviewed paper that you would like to write about? Please send suggestions to Mind Matters editor Gareth Cook, a Pulitzer prize-winning journalist at the Boston Globe. He can be reached at garethideas AT gmail.com or Twitter @garethideas .

FTLOScience

Do Plants Feel Pain? A Biochemical Perspective

Plants are scientific enigmas; they are all around us, and yet we barely take notice of their existence. We know relatively little about how they respond to their environments because, well, it’s not like they can interact with us directly. Using invisible signaling mechanisms, they communicate messages across huge distances from their roots to their leaves, and even with each other! But do they have a ‘sense’ of touch, and can plants feel pain?

Plants don’t feel pain because they lack a central nervous system. However, they do respond to stress and touch through signaling mechanisms. The produce hormones in response to ‘pain’, affecting the way they grow and signaling to other plants about incoming danger.

What Goes on Inside a Plant?

There are approximately 391,000 species of plants in the world, and around 2,000 new species are discovered each year 1 . On Earth, plants make up over 80% of the combined mass of all living organisms 2 . Despite their proliferation around us, we tend to disregard their lofty status within the natural world.

Many vegans argue that it is more ethical to eat plants because they do not feel pain, hence sparing animals the cruelty that is associated with their slaughter for consumption. Regardless of whether you think it’s ethical or not, it’s a good idea to eat less meat because it also considerably reduces your carbon footprint . However, is it really true that plants do not feel pain? To answer the question, we first need to explore how plants work.

Anatomy of a Plant

For simplicity’s sake, let’s only consider the type of plant we are most familiar with—vascular plants. These are plants that are able to distribute water, nutrients and photosynthates (products of photosynthesis) around the plant through a system of vessels, as opposed to non-vascular plants that rely on osmosis to transport water and nutrients. The main highways of plant transport consist of vascular tissue; xylem cells transporting water and phloem cells transporting nutrients and minerals up and down the stem.

Vascular plants also tend to have roots and leaves; nutrients and water from the soil are drawn in through the roots, while sucrose is produced in the leaves via photosynthesis and transported to the rest of the plant.

Transporting nutrients around when you have a sound infrastructure in place sounds simple enough, but a closer look reveals an impressive array of signaling mechanisms. These allow plants to perform tasks more efficiently and simply do what plants do best: photosynthesize and grow.

The Sense of Touch

How can we tell that plants are able to ‘sense’ their immediate environment? If you have ever seen a vine wrapped around anything that happens to be sitting nearby, then you’ve witnessed this in action. Similarly, some trees exhibit a phenomenon known as crown shyness whereby their canopies avoid touching.

One unique plant which truly demonstrates the ability of plants to react to touch is the touch-me-not plant ( Mimosa pudica ), which has leaves that close when brushed—a fascinating example of rapid plant movement. There’s ample evidence to suggest that plants respond to touch, but some of the mechanisms behind this remain unclear. We tend to think of plants as slow and unresponsive, but these examples definitely show otherwise.

Do Plants Feel Pain?

Animals—including humans—hunt when they are hungry, recoil when they feel pain, and look for shelter from heat and rain. These responses to stimuli are possible only because our bodies contain a collection of signaling mechanisms known as the nervous system. Neurons transmit electric signals around our body with the brain acting as the main processing center. Basically, this allows us to quickly react and adjust to unfavorable conditions.

Without neurons, synapses or even a brain, plants lack a strict nervous system. Hence, they are unable to feel pain in the traditional sense. However, they seem to still be able to respond to external physical stimuli. It is no surprise then that plants have developed their own set of responses to ‘pain’. After all, they already have a few hundred million years of survival and evolution under their belt!

finger touching a mimosa pudica touch me not plant

Plant Responses to ‘Pain’

Altering their genes.

When plants are touched, certain genes in their DNA are expressed, which in turn changes the way they grow. Since plants are unable to ‘move’ away from the cause of the stimuli, the only way they can protect themselves is to change their own physiology. A 2016 study found that spraying water onto plants initiated changes in gene expressions within just a few minutes 3 !

Similar reactions were caused when the leaves were touched, cut with scissors, blown with a hairdryer or placed in shadow. Although the outward appearance of the plants did not appear to change when observed immediately after the stimulus, it was clear that the plants that were touched daily over a long period of time experienced stunted growth compared to plants that were left alone.  

Methyl Jasmonate: The Pain Hormone

These changes in growth are caused by the release of plant hormones (signal molecules that control the growth and development of the plant). One hormone which could play an important role in this process is methyl jasmonate, an ester derivative of the hormone jasmonate.

Methyl jasmonate is a lipid hormone in plants that regulates many different processes, but its best-studied role is as a response to attacks. When a hungry herbivore comes along to munch on a plant’s leaves, the methyl jasmonate biosynthetic pathway kicks in. The increase in methyl jasmonate within the plant causes changes in the expression of certain genes.

In the tomato plant, for example, this activates genes that make its leaves harder to digest 4 . Furthermore, the closely related jasmonic acid can travel through the air, inducing nearby plants to synthesize defensive compounds before a potential attack – an interesting form of plant communication!

red tomatoes in basket

One 2012 study found that plants that produced jasmonate flowered later, grew shorter stems and produced smaller clusters of leaves when touched, while plants that did not produce jasmonate grew normally 5 . The same study determined that, despite the detrimental effect of jasmonate synthesis on growth, plants that were touched exhibited a stronger ability to respond to insect attacks and fungal infections.

Apart from deterring attackers and stunting plant growth, jasmonate also causes other effects through the expression of certain genes. These include genes that govern reproduction (either promoting or delaying fertility) and genes that code for nutrient storage. Many of these mechanisms and pathways are the subject of current research.

Role of Calcium Ions

One hypothesis involves calcium ions, which already play an important role in animals as a messenger in cell signaling. A 2018 study found that when a leaf was cut, an increase in calcium concentration was triggered by the release of glutamate (an amino acid that acts as a neurotransmitter in vertebrates).

This increase was observed to originate next to the wound and was subsequently spread around the plant, signaling the location of the cut 6 . What this means is that the way plants communicate internally and the way animal nervous systems work can, in fact, be more similar than we think.

Mechanosensitive Channels

A related hypothesis looks at mechanosensitive channels; these are proteins that open or close pores in response to mechanical deformation of the cell membrane. When the pores are open, electrically conductive ions are able to diffuse into or out of the cell 7 .

In animals, these actions act as signals which in turn generate sensory perceptions; in plants, it is believed that the opening of the channels allows calcium ions to pass through the cell, triggering responses to protect against the physical stimuli. 

The touch-me-not ( Mimosa pudica ) mentioned earlier is able to ‘perceive’ touch through such mechanosensitive channels. A structure known as the pulvinus sits at the base of each leaf where it meets the stem, and mechanical stimulation causes an outward flux of ions 8 .

By osmosis, water quickly exits the structure, leading to a fall in pressure inside the pulvinus and causing the leaves to close. Water can re-enter the pulvinus but this is a much slower process, taking up to 20 minutes before the touch-me-not plant can open its leaves again.

Should We Still Eat Vegetables?

So yes, it’s obvious that plants can sense when they are touched. However, the mechanisms behind intercellular communication in plants are complex and still largely unexplored, and there is much ongoing research examining how plants can respond to stimuli. Do plants feel pain as we perceive it?

While we do have some idea of what happens internally when a plant is damaged, we cannot compare it to the way animal systems respond to injury because plants do not have a central nervous system. Therefore, it is entirely possible that plants feel pain, but definitely not in the way we are familiar with.

But whatever your ethical standing on plants and their feelings, the truth remains that a fruit and vegetable-heavy diet lowers your risk for all sorts of diseases . And if you really want to live a longer, healthier life, plants should make up at least 50% of all your meals 9 !

Now, please excuse me while I eat a carrot.

  • Thorn, J. & Royal Botanical Gardens, Kew. (2016). State of the World’s Plants 2016. Retrieved from https://www.researchgate.net/publication/320673453_State_of_the_World’s_Plants_2016
  • Pennisi, E. (2018). Plants outweigh all other life on Earth. Retrieved from https://www.sciencemag.org/news/2018/05/plants-outweigh-all-other-life-earth
  • Nolch, G. (2016). Plants respond to touch. Australasian Science, 37 (6), 7.
  • Farmer, E. E., & Ryan, C. A. (1990). Interplant communication: airborne methyl jasmonate induces synthesis of proteinase inhibitors in plant leaves. Proceedings of the National Academy of Sciences , 87(19), 7713-7716.
  • Grens, K. (2012). How Plants Feel. The Scientist, 26 (12), 50.
  • Toyota, M., Spencer, D., Sawai-Toyota, S., Jiaqi, W., Zhang, T., Koo, A. J., Howe, G. A., & Gilroy, S. (2018). Glutamate triggers long-distance, calcium-based plant defense signalling. Science, 361 , 1112-1115.
  • Fischer, W. B., Wang, Y-T., Schindler, C., & Chen, C-P. (2012). Mechanism of Function of Viral Channel Proteins and Implications for Drug Development. International Review of Cell and Molecular Biology, 294 , 259-321.
  • Fleurat-Lessard, P., Frangne, N., Maeshima, M., Ratajczak, R., Bonnemain, J. L., & Martinoia, E. (1997). Increased expression of vacuolar aquaporin and H+-ATPase related to motor cell function in Mimosa pudica L. Plant Physiology , 114(3), 827-834.
  • Federal Occupational Health. (n.d.). THE ORIGINAL RENEWABLE ENERGY SOURCE. Retrieved from https://foh.psc.gov/calendar/nutrition.html

About the Author

Linda FTLOScience editor

Linda is a writer with a love for physics, chemistry and debunking science misconceptions. She holds a Bachelor of Science and a Master of Publishing. Her hobbies include photography, hiking and watching Netflix on a Saturday night.

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New research on plant intelligence may forever change how you think about plants

research on plants feeling pain

Plants, like these sunflowers, have proven to have amazing sensory abilities, but scientists aren’t exactly sure how.

The Intelligent Plant. That is the title of a recent article in The New Yorker — and new research is showing that plants have astounding abilities to sense and react to the world.

But can a plant be intelligent?  Some plant scientists insist they are — since they can sense, learn, remember and even react in ways that would be familiar to humans.

Michael Pollan , author of such books as "The Omnivore's Dilemma" and "The Botany of Desire," wrote the New Yorker piece about the developments in plant science. He says for the longest time, even mentioning the idea that plants could be intelligent was a quick way to being labeled "a whacko." But no more, which might be comforting to people who have long talked to their plants or played music for them.

The new research, he says, is in a field called plant neurobiology — which is something of a misnomer, because even scientists in the field don't argue that plants have neurons or brains.

"They have analagous structures," Pollan explains. "They have ways of taking all the sensory data they gather in their everyday lives … integrate it and then behave in an appropriate way in response. And they do this without brains, which, in a way, is what's incredible about it, because we automatically assume you need a brain to process information."

And we assume you need ears to hear. But researchers, says Pollan, have played a recording of a caterpillar munching on a leaf to plants — and the plants react. They begin to secrete defensive chemicals — even though the plant isn't really threatened, Pollan says.  "It is somehow hearing what is, to it, a terrifying sound of a caterpillar munching on its leaves."

Pollan says plants have all the same senses as humans, and then some. In addition to hearing, taste, for example, they can sense gravity, the presence of water, or even feel that an obstruction is in the way of its roots, before coming into contact with it. Plant roots will shift direction, he says, to avoid obstacles.

So what about pain? Do plants feel? Pollan says they do respond to anesthetics. "You can put a plant out with a human anesthetic. … And not only that, plants produce their own compounds that are anesthetic to us." But scientists are reluctant to go as far as to say they are responding to pain.

How plants sense and react is still somewhat unknown. They don't have nerve cells like humans, but they do have a system for sending electrical signals and even produce neurotransmitters, like dopamine, serotonin and other chemicals the human brain uses to send signals.

"We don't know why they have them, whether this was just conserved through evolution or if it performs some sort of information processing function. We don't know. There's a lot we don't know," Pollan says.

And chalk up another human-like ability — memory. 

Pollan describes an experiment done by animal biologist Monica Gagliano. She presented research that suggests the mimosa pudica plant can learn from experience. And, Pollan says, merely suggesting a plant could learn was so controversial that her paper was rejected by 10 scientific journals before it was finally published.

Mimosa is a plant, which looks something like a fern, that collapses its leaves temporarily when it is disturbed.  So Gagliano set up a contraption that would drop the mimosa plant, without hurting it. When the plant  dropped, as expected, its leaves collapsed. She kept dropping the plants every five to six seconds.

"After five or six drops, the plants would stop responding, as if they'd learned to tune out the stimulus as irrelevent," Pollan says. "This is a very important part of learning — to learn what you can safely ignore in your environment."

Maybe the plant was just getting worn out from all the dropping? To test that, Gagliano took the plants that had stopped responding to the drops and shook them instead. 

"They would continue to collapse," Pollan says. "They had made the distinction that [dropping] was a signal they could safely ignore. And what was more incredible is that [Gagliano] would retest them every week for four weeks and, for a month, they continued to remember their lesson."

That's as far out as Gagliano tested. It's possible they remember even longer. Conversely, Pollan points out, bees that are given a similar dishabituation test forget what they've learned in as little as 48 hours.

Pollan says not everyone accepts that what Gagliano describes is really learning. In fact, there are many critics with many alternative theories for explaining the response the plants are having. Still …

"Plants can do incredible things. They do seem to remember stresses and events, like that experiment. They do have the ability to respond to 15 to 20 environmental variables," Pollan says. "The issue is, is it right to call it learning?  Is that the right word? Is it right to call it intelligence?  Is it right, even, to call what they are conscious . Some of these plant neurobiologists believe that plants are conscious — not self-conscious, but conscious in the sense they know where they are in space … and react appropriately to their position in space."

Pollan says there is no agreed definition of intelligence. "Go to Wikipedia and look up intelligence. They despair of giving you an answer. T hey basically have a chart where they give you nine different definitions. And about half of them depend on a brain — they refer to abstract reasoning or judgment.

"And the other half merely refer to a problem-solving ability. And that's the kind of intelligence we are talking about here. … So intelligence may well be a property of life. And our difference from these other creatures may be a matter of difference of degree rather than kind. We may just have more of this problem-solving ability and we may do it in different ways."

Pollan says that really freaks people out — "that the line between plants and animals might be a little softer than we traditionally think of it as."

And he suggests that plants may be able to teach humans a thing or two, such as how to process information without a central command post like a brain.

Check out this video of Michael Pollan discussing time-lapse photography of bean plants looking very purposeful.

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  • DOI: 10.2478/disp-2020-0003
  • Corpus ID: 220634237

Do Plants Feel Pain?

  • A. Hamilton , Justin P. McBrayer
  • Published 1 May 2020
  • Environmental Science, Philosophy, Biology

7 Citations

Debunking a myth: plant consciousness, a critical review of plant sentience: moving beyond traditional approaches, aesthetic animism, is a vegetarian diet morally safe, why social robots need self-preservation to be objects of moral consideration, what are the red flags for neural network suffering, a biosemiotic reading of michel onfray’s cosmos: rethinking the essence of communication from an ecocentric and scientific perspective, 62 references, do animals feel pain, are plants sentient, the mind behind anthropomorphic thinking: attribution of mental states to other species, mortal questions: what is it like to be a bat, mind in life : biology, phenomenology, and the sciences of mind, plant neurobiology: no brain, no gain, consciousness and experience, on seeing human: a three-factor theory of anthropomorphism., theory of mind and autism: a review, the opacity of mind: an integrative theory of self-knowledge, related papers.

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Plants feel pain and might even see.

It’s time to retire the hierarchical classification of living things.

  • By Peter Wohlleben
  • July 21, 2021

Wohlleben_HERO

I n 2018, a German newspaper asked me if I would be interested in having a conversation with the philosopher Emanuele Coccia, who had just written a book about plants, Die Wurzeln der Welt (published in English as The Life of Plants ). I was happy to say yes.

The German title of Coccia’s book translates as “The Roots of the World,” and the book really does cover this. It upends our view of the living world, putting plants at the top of the hierarchy with humans down at the bottom. I had been giving a great deal of thought to this myself. Ranking the natural world and scoring species according to their importance or their superiority seemed to me outdated. It distorts our view of nature and makes all the other species around us seem more primitive and somehow unfinished. For some time now, I have not been comfortable with viewing humans as the crown of creation, separating animals into higher and lower life-forms, and treating plants as something on the side, definitively banished to a lower level.

And so I found the conversation with Coccia most refreshing when he visited our Forest Academy . A small bearded man, Coccia turned up in a blue suit and blue checkered tie, completely inappropriate attire for the outdoors, even though we had agreed that we would take a walk in the forest together. Although he is from Italy and now teaches in France and writes in French, he also speaks fluent German because at one time he studied and worked in Freiburg.

research on plants feeling pain

After our first cup of coffee, we were soon deep into our main topic: trees and plants in general. Coccia argued that our biological classifications are not grounded in science. They are strongly influenced by theology and are dominated by two ideas: the supremacy of the human race and the world as a place humans must bend to their will. And then there is our centuries-old compulsion to categorize everything. When you combine these concepts, you get a ranking system that puts humankind at the top, animals in the middle, and plants way down at the bottom.

I listened, fascinated by what he had to say. Here was a man of my own heart. I would prefer it, I told Coccia, if science categorized species one beside the other. That would still allow an order, a system of sorting, without imposing any kind of a hierarchy. He immediately agreed. He reiterated his belief that the ordering system we have today is not scientific but rather influenced by cultural, historical, and religious values. For Coccia, the hard boundary between the plant and animal world does not exist. He believes plants can experience sensations and even reflect on them. And he is not the only one who thinks this.

Did the plants wake up as we do when we come to after a general anesthetic?

František Baluška is also very good at making inconceivable connections. Baluška, a plant cell biologist at University of Bonn, has for some time now been of the opinion that plants are intelligent—after all, they can process information and make decisions. But do plants have consciousness? That takes the discussion to a whole different level. If we could prove that plants have consciousness, we would have to radically change the way we interact with them, because we’d find ourselves facing the same kinds of issues that we face with factory farming in conventional agriculture.

Baluška, together with colleagues from around the world, including Stefano Mancuso from the University of Florence, has come a little closer to answering the question about plant consciousness. Baluška and his colleagues sedated plants that feature moving parts, such as Venus flytraps. These plants catch their prey in a trap that snaps shut as soon as insects touch trigger hairs on the inner side of their double-lobed leaves. The two sides of the leaf fold together in a flash, capturing the insect between them, and the plant then digests its prey. The anesthetics the scientists used, which included some that are used on people, deactivated electric activity in the plants so that the traps no longer reacted when they were touched. Sedated peas showed similar changes in behavior. Their tendrils, which usually move in all directions as they slowly feel their way through their surroundings to find supporting structures to grow on, stopped searching and started to spiral on the spot. After the plants broke the narcotics down, they resumed their normal behavior.

Did the plants wake up as we do when we come to after a general anesthetic? This is the critical question, because in order to wake up, you need one thing above all others: consciousness. And it was exactly this question that a reporter from The New York Times posed to Baluška. I really liked his answer: “No one can answer this because you cannot ask [the plants].”

I excitedly imagined what Baluska’s kind of plant research would look like: well-equipped laboratories with plants all over the place monitored by elaborate apparatuses finally giving up their secrets. That was something I absolutely had to see. On a sunny afternoon in 2018, I parked my car in front of his institute. I took a musty-smelling elevator to the fourth floor. Then (according to the email I received from Baluška), I was to turn right when I stepped out of the elevator and take a flight of wooden stairs up to his office. The corridor straight in front of the elevator door led to neat, uniformly gray rooms of the kind you expect to see in universities. The wooden staircase to the right led to an out-of-the-way corner in the huge building complex. Up there, on a tiny landing, Baluška greeted me with his strong Slovakian accent.

He led me into the conference room and we sat side by side at a huge round table. I was eager to hear what he had to say. After all, I had cited his research in my book The Hidden Life of Trees and repeatedly mentioned his groundbreaking research when I attended events. His results sounded so fantastic that I sometimes wondered if I had interpreted them correctly when I translated them into everyday language for the general public. Baluška immediately put my fears to rest.

One of the first things we talked about was how plants feel pain. Fellow foresters roll their eyes when I talk about spruce feeling pain when they are attacked by bark beetles. “Of course a plant, trees can feel pain,” the professor answered when I asked him about it. “Every life form must be able to do that in order to react appropriately.” He explained that there is evidence for this at the molecular level. Like animals, plants produce substances that suppress pain. He doesn’t see why that would be necessary if there was no pain.

Baluška was ready with other quite different discoveries. There’s a vine that grows in South America that adapts to the form of the tree or bush it is climbing on. Its leaves look just like the leaves on the host plant. You might think this is chemically controlled. In that case, the vine might be detecting scent compounds from the bush and changing the shape of its leaves in a way that was genetically predetermined. Three different leaf shapes had been observed. Then a researcher came up with the idea of creating an artificial plant with plastic leaves and relocating our botanical chameleon to its new home. What happened next was amazing. The vine imitated the artificial leaves, just as it had imitated the leaves in nature. For Baluška this is clear proof that the vine can see. How else could it get information about a shape it had never encountered before? In this case, the usual suspects—chemical messages released by the host plant or electric signals between both plants—were absent. He went further. In his opinion, it is conceivable that all plants might be able to see.

Forests need foresters? Trees have existed for more than 300 million years, modern humans for 300,000.

Up until then, the only thing I knew was that trees can differentiate between light and dark. Sleep behavior has been researched in birches and oaks, and beeches can measure day length—all of this requires light receptors that transmit signals to the trees and spur the whole organism into action. This is far removed, though, from vision in the sense of being able to recognize shapes and colors. And now this: plants which register precisely that and change their behavior accordingly. I found that astonishing.

Baluška directed me to research being done on the cuticle or outer layer of leaves. On most plants, this layer is completely transparent, which makes no sense if all the leaves are doing is collecting light to manufacture sugar. In that case, these outer cells should be equipped with green chloroplasts, the organs used for photosynthesis—after all, this is where the most sunlight falls. Logically, less light is harvested in layers farther from the surface. And yet the cuticle is transparent, which seems wasteful. Not only that. In several plants, the cuticle is constructed in the shape of a lens, which means that it focuses light, making the cuticle functionally similar to the lens in our eye. It doesn’t seem logical to me to focus light if photosynthesis is the only goal, because the cuticle could simply let the sun’s rays through. Focusing light doesn’t increase how much light falls on a leaf. The same amount of light is simply more concentrated or, more specifically, focused more intensely to the back of the cell.

Leaves that function like eyes? There’s an idea that takes some getting used to, particularly as a tree regularly discards its “eyes” in the autumn when its leaves fall off. Does that make leaves disposable eyes? In a certain sense, yes. A working life of six months (under European climate conditions) is relatively long in comparison with some animals. Flies, for example, use their eyes for little more than a month simply because that’s how long they live. And mayflies, which live for barely a day after metamorphosing from a larva into a flying insect, use their visual apparatus for less than 24 hours—and yet the eyes they have are real.

There’s another thing with trees. The cells in the leaves, once they are formed, last for the whole growing season, which means they are relatively long lived. In contrast, our eyes are in a constant state of partial rejuvenation: The cells in the outer cornea, for instance, are completely replaced every seven days.

Y ou would think that plants experiencing pain and now the hypothesis that they might even be able to see would put the whole scientific community into a state of high excitement. The reaction, however, was muted. I had assumed that plant neurobiology was an up-and-coming scientific field. Baluška shook his head. He was practically the only one still studying the topic in depth. And that means this branch of science could disappear and be forgotten for a second time.  The first time it disappeared was back in Darwin’s day.

Darwin had studied plant roots and even back then he postulated that the tips might function like the brains of simple animals. Roots containing “tiny brains”? The hard boundary between animal and plant could have fallen in his time. Could have. The research was put on hold for a hundred years and then suffered another blow from which it has not recovered to this day. The blow came in the form of a well-intentioned book by Peter Tompkins and Christopher Bird entitled The Secret Life of Plants , published in 1973. It was based on experiments that were not reproducible and definitely strayed from science into the mystic.

He went further. In his opinion, it is conceivable that all plants might be able to see.

There was, however, another problem, Baluška explained. All the research on nerves, the brain, and phenomena such as pain had originally been done on people. All the important biological terminology, therefore, was already taken. This meant it would not be scientifically correct to transfer the definitions to plants that exhibited very similar structures and processes. And so, neurobiology was reserved for animals, which is why a similar periodical for plant research is called Plant Signaling & Behavior and not Plant Neuroscience . I immediately thought that philosophy and biology should be more closely connected, because Coccia’s thoughts on the subject matched those of Baluška.

The path to greater harmony between all life forms is long and turns on perspective and scientific clarity. For example, the more I think about the differences between conventional forestry and the original ecosystems of the forest, the more I conclude that the differences rest on a big misunderstanding. Conventional foresters believe that they are protecting ecosystems and through their stewardship are imitating or at most speeding up natural processes. However, the understanding of these ecosystems is grounded in a different philosophy about natural processes, in short in a different definition of evolution. This definition goes back to Darwin and his colleagues, who coined the phrase “survival of the fittest.” However, that doesn’t mean every life form fights every other life form and the strongest prevails. Rather, it’s more about being able to thrive in an environment and reproduce successfully. That is a completely different interpretation of “survival of the fittest” and means, for example, that social communities can also be very successful in nature.

Trees and wolves—and especially our own species—prove how successful social communities can be. A more accurate rendering of the phrase would be “survival of the most well adapted” (“fittest” in the sense of being the best fit rather than the strongest), which means survival of the species that manage best in the environment in which they find themselves. If that were not the case, evolution would mean that ever stronger and therefore perhaps also more aggressive species would be the ones that survived. If you read the phrase as the strong species surviving best, you would expect earlier species to have been underdeveloped, whereas in reality they were well adapted to the conditions that prevailed at the time. But because nature is always in flux, continents wander, and climate changes, the appearance and disappearance of species is not evolution in the sense of improvement but simply in the sense of adapting to new environmental conditions.

I, for one, used to interpret the phrase completely differently and thought that species were constantly improving until we finally got to us. And so, according to this outdated understanding, the logical conclusion was that humans stood at the pinnacle of creation. From a scientific point of view, however, this conclusion is incorrect. Its current meaning can only be explained from a cultural and religious perspective. And when we get to trees, we have got the wrong end of the stick completely, just like many foresters.

Foresters believe that trees not only of different species but also of the same species fight each other for light, water, and food. In managed forests, foresters get involved in what they think is the fight that plays out in undisturbed forests. You could say they see themselves as the referees. In Germany, I have often heard them say that the native forests could not survive without foresters. And yet, trees have existed for more than 300 million years, modern humans for 300,000, and the profession of forestry for just 300. For most of the time, trees have managed very well without human referees—in no small part because they have not been fighting.

And here I return to Coccia. He thinks it is a great shame that for the past 100 years we’ve seen nature as a huge war zone in which everyone is fighting everyone else. But, according to Coccia, nature is not a war zone. On the contrary, it is characterized by solidarity. To that thought, I have nothing to add.

Peter Wohlleben is the author of numerous books, including the New York Times bestseller The Hidden Life of Trees, and its follow-ups, The Inner Life of Animals and The Secret Wisdom of Nature. He is also the author of books for children including Can You Hear the Trees Talking? and Peter and the Tree Children. When he’s not writing, Wohlleben manages a sustainable forest and runs a forest academy near Germany’s Eifel Mountains.

Excerpted and adapted from The Heartbeat of Trees: Embracing Our Ancient Bond With Forests and Nature , by Peter Wohlleben, available now from Greystone Books. Excerpted by permission of the publisher.

Lead image: Fona / Shutterstock

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Plants Really Do Respond to The Way We Touch Them, Scientists Reveal

research on plants feeling pain

It's something that plant lovers have long suspected, but now Australian scientists have found evidence that plants really can feel  when we're touching them.

Not only that, but different sensations trigger a cascade of physiological and genetic changes, depending on the stimulation the plants are receiving, whether it's a few drops of rain, or a little soft pat, which is probably the coolest thing we've heard all week.

"Although people generally assume plants don't feel when they are being touched, this shows that they are actually very sensitive to it," said lead researcher Olivier Van Aken from the University of Western Australia.

"While plants don't appear to complain when we pinch a flower, step on them or just brush by them while going for a walk, they are fully aware of this contact and are rapidly responding to our treatment of them," he added.

But first thing's first, let's not get ahead of ourselves and anthropomorphise the crap out of this situation, as we humans love to do. Although this whole thing sounds super adorable and touchy feely, plants don't have brains and they don't 'think'.

We also don't have evidence to suggest that they actually 'feel' in any way resembling our perception of the sense.

That said, previous research has shown that plants do have pretty good awareness of their surroundings. For example, they can 'hear' when they're being chewed on by insects, and release chemicals to stop it. And they're also able to communicate with each other via a subterranean 'internet' of fungus. 

While there's no visible response to any of this stimulus, what this input does is help the plant stay aware of its surroundings and prepare itself for any potential danger, or get ready to take advantage of changing weather conditions. 

One thing the scientists found was that spraying water droplets on plants caused them to change the expression of thousands of genes - a dramatic physiological response that started within minutes of the stimulus and stopped within half an hour. 

"We were able to show that this response was not caused by any active compounds in the spray but rather by the physical contact caused by water drops landing on the leaf surface," says Van Aken.

Curious to know how else they might respond, the team also found that gently patting the plants or touching them with tweezers could trigger a similar physiological cascade. So could a sudden shadow falling over their leaves.

All of this information could be essential to plants survival in the wild, the researchers explain in the journal  Plant Physiology.

"Unlike animals, plants are unable to run away from harmful conditions. Instead, plants appear to have developed intricate stress defence systems to sense their environment and help them detect danger and respond appropriately," says Van Aken.

Importantly, the study also identified two proteins that could switch off the plant's touch response. In the future, this could help plants in controlled environments, such as greenhouses, from changing their genes and responding to 'false alarm' stimuli.

One study on its own obviously isn't enough to overhaul our understanding of plant stimulation perception, and more research is needed to replicate the finds. But for now, maybe we should all be more thoughtful when we're prodding and poking our plants, or blocking their light with our giant human heads.

The good news?  Singing seems to be pretty safe. "As yet, there's no evidence to back the idea held by some people that the vibrations caused by just talking to plants has a strong enough effect to move plants," Van Aken told Peter Spinks from the  The Age .

BRB, going to sing some Frank Sinatra to my ficus.

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Do Plants Have Feelings? All Sides of the Debate

By Adilya Zaripova Categories: Environment & Nature May 29, 2023, 8:59 AM

do plants have feelings

Do plants have feelings? Can plants feel pain? If you think you know the answer, read on. You won’t believe what modern science says about it.

You won’t believe you never realized this about plants! The debate about whether or not plants have feelings continues, presenting new scientific evidence. It seems that plants use the same senses we do every day and experience the world in a very human-like way. And not only are they sensitive, but they also actively interact with the environment.

Does it mean that plants do have feelings after all? Let’s explore all the arguments.

How Do Feelings Work?

Just like humans, animals are sentient and definitely have feelings.

What are feelings, and why do we have them? A feeling is generally defined as a physical or emotional experience or awareness. In neurology, feelings are what arise as our brain interprets emotions . While emotions themselves are physical signals of the body reacting to external or internal triggers.

To understand how feelings work, think of a moment when something surprised you. Surprise is one of the basic emotions that represents our body’s reaction to something unexpected. It causes your heart to race and changes your facial expression at that moment. But when the brain interprets this emotion, it can respond with numerous different feelings. It can be happiness, stress or even hatred, depending on what, when and where surprised you.

What we feel in a particular situation is influenced by our personal beliefs, experiences and memories. This is why people who find themselves in the same circumstance and are affected by the same emotion can have very different feelings.

The human capacity to feel and experience the world subjectively is what makes us sentient. Sentience essentially means the capacity to have feelings. It requires a level of self-awareness and cognitive ability. Multiple studies prove that animals are also sentient beings who can experience positive and negative feelings.

What about plant sentience ? Do plants have feelings? Here is what research says about it.

Do Plants Have Feelings?

Trees have their own "language" and can talk to each other.

Years of botanical research have proven that, unlike animals and humans, plants don’t have brains and nervous systems — in other words, they are unable to have a brain response that we define as a feeling. However, research has also shown that many plants respond to stimulation by sending and receiving electrical signals from and to various areas of their bodies. Some researchers refer to this capability as the “nervous system of plants”, but they emphasize that it works very differently from the human nervous system.

In their 1973 book The Secret Life of Plants , Peter Tompkins and Christopher Bird documented experiments that claimed to prove plant sentience and the ability of plants to communicate. The book generated a lot of media attention. But the experiments were deemed controversial, and the whole topic of plant sentience became a joke in the field of plant biology.

Recent studies suggest that this joke might actually have some truth to it. They show that trees do communicate in their own way. And some plants are capable of transmitting ultrasonic sounds. Though it’s not clear yet if they are using these sounds to talk to each other.

Facts about trees.

Facts about trees are surprisingly similar to facts about humans. They are very much alive and a vital link in…

Do Plants Feel Pain?

Is this dew or tears of pain?

Anatomically speaking, plants can’t feel pain since they don’t have pain receptors or brains . We use pain as a defense mechanism to help us either “fight” or “flight” when faced with danger. Since plants don’t have this ability, it seems logical that they don’t have a biological need for pain. Can we be sure, though?

No, we can’t. Whether or not plants feel pain or have feelings is still an open question at this point in the research. According to some studies, they might be experiencing the world very similarly to us, using the same basic senses.

Plants can touch

Climbing plants touch things around them to find support and grow. Others get stressed if touched and react immediately. The “touch-me-not” flower, Mimosa pudica , folds its leaves to prevent damage.

Plants can hear

Studies prove that plants can sense sounds and even display certain behaviors when they “hear” something. When some flowers detect bees buzzing, they produce sweeter nectar to increase the chances of cross-pollination.

plant facts

Think you’re a bonafide plant expert? We’ll see! From carnivorous plants to the Tree of Life, expand your knowledge of…

Plants can taste

Most plants don’t eat like humans or animals, though some come close. Think of Dionaea muscipula , also known as Venus flytrap, a carnivore plant capable of luring and catching prey. Besides, plants can “ taste” soil with their roots to find nutrients in it and avoid rooting near toxic substances.

Plants can smell

Plants don’t need a nose to smell. They receive information from odor molecules and use it to adapt to environmental challenges. Some studies even claim that they can “ sniff” one another’s chemical signals and detect threats.

Plants can see

No, plants don’t have eyes. But that doesn’t mean they can’t see. Plants can detect many different forms of light , from ultraviolet to infrared. Using this ability, sunflowers track the sun from east to west during the day and then reorient during the night to face the dawn.

What Should We Do if Plants Have Feelings?

Nature makes us feel happy. But do plants share our feelings?

One thing is certain: plants are living, extraordinary beings. They have an incredible ability to sense the surrounding world and react to sunlight, gravity, wind, damage and temperature changes. There is no doubt that plants get stressed in bad environments . What’s even more amazing is that they produce their own anesthetic substances to lessen their injuries when wounded or under attack.

But does it mean that plants have feelings? Modern research that relies on human understanding of emotional reactions certainly concludes that plants don’t feel pain or have any other feelings. Yet the debate is far from over.

Regardless of what the final answer is, it wouldn’t change the fact that a plant-based diet is the most plant-friendly nutritional choice you can make. By going vegan , you can reduce your carbon footprint, which is a great way to help the planet and its flora.

Read more: 

  • Best Fertilizer for Fruit Trees: Per Age and Tree Type
  • 11 Flowers for Bees: Turn Your Garden or Balcony Into a Bee Paradise
  • Benefits of Going Vegetarian: Simple Tips for Beginners

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Human Subjects Office

Medical terms in lay language.

Please use these descriptions in place of medical jargon in consent documents, recruitment materials and other study documents. Note: These terms are not the only acceptable plain language alternatives for these vocabulary words.

This glossary of terms is derived from a list copyrighted by the University of Kentucky, Office of Research Integrity (1990).

For clinical research-specific definitions, see also the Clinical Research Glossary developed by the Multi-Regional Clinical Trials (MRCT) Center of Brigham and Women’s Hospital and Harvard  and the Clinical Data Interchange Standards Consortium (CDISC) .

Alternative Lay Language for Medical Terms for use in Informed Consent Documents

A   B   C   D   E   F   G   H   I  J  K   L   M   N   O   P   Q   R   S   T   U   V   W  X  Y  Z

ABDOMEN/ABDOMINAL body cavity below diaphragm that contains stomach, intestines, liver and other organs ABSORB take up fluids, take in ACIDOSIS condition when blood contains more acid than normal ACUITY clearness, keenness, esp. of vision and airways ACUTE new, recent, sudden, urgent ADENOPATHY swollen lymph nodes (glands) ADJUVANT helpful, assisting, aiding, supportive ADJUVANT TREATMENT added treatment (usually to a standard treatment) ANTIBIOTIC drug that kills bacteria and other germs ANTIMICROBIAL drug that kills bacteria and other germs ANTIRETROVIRAL drug that works against the growth of certain viruses ADVERSE EFFECT side effect, bad reaction, unwanted response ALLERGIC REACTION rash, hives, swelling, trouble breathing AMBULATE/AMBULATION/AMBULATORY walk, able to walk ANAPHYLAXIS serious, potentially life-threatening allergic reaction ANEMIA decreased red blood cells; low red cell blood count ANESTHETIC a drug or agent used to decrease the feeling of pain, or eliminate the feeling of pain by putting you to sleep ANGINA pain resulting from not enough blood flowing to the heart ANGINA PECTORIS pain resulting from not enough blood flowing to the heart ANOREXIA disorder in which person will not eat; lack of appetite ANTECUBITAL related to the inner side of the forearm ANTIBODY protein made in the body in response to foreign substance ANTICONVULSANT drug used to prevent seizures ANTILIPEMIC a drug that lowers fat levels in the blood ANTITUSSIVE a drug used to relieve coughing ARRHYTHMIA abnormal heartbeat; any change from the normal heartbeat ASPIRATION fluid entering the lungs, such as after vomiting ASSAY lab test ASSESS to learn about, measure, evaluate, look at ASTHMA lung disease associated with tightening of air passages, making breathing difficult ASYMPTOMATIC without symptoms AXILLA armpit

BENIGN not malignant, without serious consequences BID twice a day BINDING/BOUND carried by, to make stick together, transported BIOAVAILABILITY the extent to which a drug or other substance becomes available to the body BLOOD PROFILE series of blood tests BOLUS a large amount given all at once BONE MASS the amount of calcium and other minerals in a given amount of bone BRADYARRHYTHMIAS slow, irregular heartbeats BRADYCARDIA slow heartbeat BRONCHOSPASM breathing distress caused by narrowing of the airways

CARCINOGENIC cancer-causing CARCINOMA type of cancer CARDIAC related to the heart CARDIOVERSION return to normal heartbeat by electric shock CATHETER a tube for withdrawing or giving fluids CATHETER a tube placed near the spinal cord and used for anesthesia (indwelling epidural) during surgery CENTRAL NERVOUS SYSTEM (CNS) brain and spinal cord CEREBRAL TRAUMA damage to the brain CESSATION stopping CHD coronary heart disease CHEMOTHERAPY treatment of disease, usually cancer, by chemical agents CHRONIC continuing for a long time, ongoing CLINICAL pertaining to medical care CLINICAL TRIAL an experiment involving human subjects COMA unconscious state COMPLETE RESPONSE total disappearance of disease CONGENITAL present before birth CONJUNCTIVITIS redness and irritation of the thin membrane that covers the eye CONSOLIDATION PHASE treatment phase intended to make a remission permanent (follows induction phase) CONTROLLED TRIAL research study in which the experimental treatment or procedure is compared to a standard (control) treatment or procedure COOPERATIVE GROUP association of multiple institutions to perform clinical trials CORONARY related to the blood vessels that supply the heart, or to the heart itself CT SCAN (CAT) computerized series of x-rays (computerized tomography) CULTURE test for infection, or for organisms that could cause infection CUMULATIVE added together from the beginning CUTANEOUS relating to the skin CVA stroke (cerebrovascular accident)

DERMATOLOGIC pertaining to the skin DIASTOLIC lower number in a blood pressure reading DISTAL toward the end, away from the center of the body DIURETIC "water pill" or drug that causes increase in urination DOPPLER device using sound waves to diagnose or test DOUBLE BLIND study in which neither investigators nor subjects know what drug or treatment the subject is receiving DYSFUNCTION state of improper function DYSPLASIA abnormal cells

ECHOCARDIOGRAM sound wave test of the heart EDEMA excess fluid collecting in tissue EEG electric brain wave tracing (electroencephalogram) EFFICACY effectiveness ELECTROCARDIOGRAM electrical tracing of the heartbeat (ECG or EKG) ELECTROLYTE IMBALANCE an imbalance of minerals in the blood EMESIS vomiting EMPIRIC based on experience ENDOSCOPIC EXAMINATION viewing an  internal part of the body with a lighted tube  ENTERAL by way of the intestines EPIDURAL outside the spinal cord ERADICATE get rid of (such as disease) Page 2 of 7 EVALUATED, ASSESSED examined for a medical condition EXPEDITED REVIEW rapid review of a protocol by the IRB Chair without full committee approval, permitted with certain low-risk research studies EXTERNAL outside the body EXTRAVASATE to leak outside of a planned area, such as out of a blood vessel

FDA U.S. Food and Drug Administration, the branch of federal government that approves new drugs FIBROUS having many fibers, such as scar tissue FIBRILLATION irregular beat of the heart or other muscle

GENERAL ANESTHESIA pain prevention by giving drugs to cause loss of consciousness, as during surgery GESTATIONAL pertaining to pregnancy

HEMATOCRIT amount of red blood cells in the blood HEMATOMA a bruise, a black and blue mark HEMODYNAMIC MEASURING blood flow HEMOLYSIS breakdown in red blood cells HEPARIN LOCK needle placed in the arm with blood thinner to keep the blood from clotting HEPATOMA cancer or tumor of the liver HERITABLE DISEASE can be transmitted to one’s offspring, resulting in damage to future children HISTOPATHOLOGIC pertaining to the disease status of body tissues or cells HOLTER MONITOR a portable machine for recording heart beats HYPERCALCEMIA high blood calcium level HYPERKALEMIA high blood potassium level HYPERNATREMIA high blood sodium level HYPERTENSION high blood pressure HYPOCALCEMIA low blood calcium level HYPOKALEMIA low blood potassium level HYPONATREMIA low blood sodium level HYPOTENSION low blood pressure HYPOXEMIA a decrease of oxygen in the blood HYPOXIA a decrease of oxygen reaching body tissues HYSTERECTOMY surgical removal of the uterus, ovaries (female sex glands), or both uterus and ovaries

IATROGENIC caused by a physician or by treatment IDE investigational device exemption, the license to test an unapproved new medical device IDIOPATHIC of unknown cause IMMUNITY defense against, protection from IMMUNOGLOBIN a protein that makes antibodies IMMUNOSUPPRESSIVE drug which works against the body's immune (protective) response, often used in transplantation and diseases caused by immune system malfunction IMMUNOTHERAPY giving of drugs to help the body's immune (protective) system; usually used to destroy cancer cells IMPAIRED FUNCTION abnormal function IMPLANTED placed in the body IND investigational new drug, the license to test an unapproved new drug INDUCTION PHASE beginning phase or stage of a treatment INDURATION hardening INDWELLING remaining in a given location, such as a catheter INFARCT death of tissue due to lack of blood supply INFECTIOUS DISEASE transmitted from one person to the next INFLAMMATION swelling that is generally painful, red, and warm INFUSION slow injection of a substance into the body, usually into the blood by means of a catheter INGESTION eating; taking by mouth INTERFERON drug which acts against viruses; antiviral agent INTERMITTENT occurring (regularly or irregularly) between two time points; repeatedly stopping, then starting again INTERNAL within the body INTERIOR inside of the body INTRAMUSCULAR into the muscle; within the muscle INTRAPERITONEAL into the abdominal cavity INTRATHECAL into the spinal fluid INTRAVENOUS (IV) through the vein INTRAVESICAL in the bladder INTUBATE the placement of a tube into the airway INVASIVE PROCEDURE puncturing, opening, or cutting the skin INVESTIGATIONAL NEW DRUG (IND) a new drug that has not been approved by the FDA INVESTIGATIONAL METHOD a treatment method which has not been proven to be beneficial or has not been accepted as standard care ISCHEMIA decreased oxygen in a tissue (usually because of decreased blood flow)

LAPAROTOMY surgical procedure in which an incision is made in the abdominal wall to enable a doctor to look at the organs inside LESION wound or injury; a diseased patch of skin LETHARGY sleepiness, tiredness LEUKOPENIA low white blood cell count LIPID fat LIPID CONTENT fat content in the blood LIPID PROFILE (PANEL) fat and cholesterol levels in the blood LOCAL ANESTHESIA creation of insensitivity to pain in a small, local area of the body, usually by injection of numbing drugs LOCALIZED restricted to one area, limited to one area LUMEN the cavity of an organ or tube (e.g., blood vessel) LYMPHANGIOGRAPHY an x-ray of the lymph nodes or tissues after injecting dye into lymph vessels (e.g., in feet) LYMPHOCYTE a type of white blood cell important in immunity (protection) against infection LYMPHOMA a cancer of the lymph nodes (or tissues)

MALAISE a vague feeling of bodily discomfort, feeling badly MALFUNCTION condition in which something is not functioning properly MALIGNANCY cancer or other progressively enlarging and spreading tumor, usually fatal if not successfully treated MEDULLABLASTOMA a type of brain tumor MEGALOBLASTOSIS change in red blood cells METABOLIZE process of breaking down substances in the cells to obtain energy METASTASIS spread of cancer cells from one part of the body to another METRONIDAZOLE drug used to treat infections caused by parasites (invading organisms that take up living in the body) or other causes of anaerobic infection (not requiring oxygen to survive) MI myocardial infarction, heart attack MINIMAL slight MINIMIZE reduce as much as possible Page 4 of 7 MONITOR check on; keep track of; watch carefully MOBILITY ease of movement MORBIDITY undesired result or complication MORTALITY death MOTILITY the ability to move MRI magnetic resonance imaging, diagnostic pictures of the inside of the body, created using magnetic rather than x-ray energy MUCOSA, MUCOUS MEMBRANE moist lining of digestive, respiratory, reproductive, and urinary tracts MYALGIA muscle aches MYOCARDIAL pertaining to the heart muscle MYOCARDIAL INFARCTION heart attack

NASOGASTRIC TUBE placed in the nose, reaching to the stomach NCI the National Cancer Institute NECROSIS death of tissue NEOPLASIA/NEOPLASM tumor, may be benign or malignant NEUROBLASTOMA a cancer of nerve tissue NEUROLOGICAL pertaining to the nervous system NEUTROPENIA decrease in the main part of the white blood cells NIH the National Institutes of Health NONINVASIVE not breaking, cutting, or entering the skin NOSOCOMIAL acquired in the hospital

OCCLUSION closing; blockage; obstruction ONCOLOGY the study of tumors or cancer OPHTHALMIC pertaining to the eye OPTIMAL best, most favorable or desirable ORAL ADMINISTRATION by mouth ORTHOPEDIC pertaining to the bones OSTEOPETROSIS rare bone disorder characterized by dense bone OSTEOPOROSIS softening of the bones OVARIES female sex glands

PARENTERAL given by injection PATENCY condition of being open PATHOGENESIS development of a disease or unhealthy condition PERCUTANEOUS through the skin PERIPHERAL not central PER OS (PO) by mouth PHARMACOKINETICS the study of the way the body absorbs, distributes, and gets rid of a drug PHASE I first phase of study of a new drug in humans to determine action, safety, and proper dosing PHASE II second phase of study of a new drug in humans, intended to gather information about safety and effectiveness of the drug for certain uses PHASE III large-scale studies to confirm and expand information on safety and effectiveness of new drug for certain uses, and to study common side effects PHASE IV studies done after the drug is approved by the FDA, especially to compare it to standard care or to try it for new uses PHLEBITIS irritation or inflammation of the vein PLACEBO an inactive substance; a pill/liquid that contains no medicine PLACEBO EFFECT improvement seen with giving subjects a placebo, though it contains no active drug/treatment PLATELETS small particles in the blood that help with clotting POTENTIAL possible POTENTIATE increase or multiply the effect of a drug or toxin (poison) by giving another drug or toxin at the same time (sometimes an unintentional result) POTENTIATOR an agent that helps another agent work better PRENATAL before birth PROPHYLAXIS a drug given to prevent disease or infection PER OS (PO) by mouth PRN as needed PROGNOSIS outlook, probable outcomes PRONE lying on the stomach PROSPECTIVE STUDY following patients forward in time PROSTHESIS artificial part, most often limbs, such as arms or legs PROTOCOL plan of study PROXIMAL closer to the center of the body, away from the end PULMONARY pertaining to the lungs

QD every day; daily QID four times a day

RADIATION THERAPY x-ray or cobalt treatment RANDOM by chance (like the flip of a coin) RANDOMIZATION chance selection RBC red blood cell RECOMBINANT formation of new combinations of genes RECONSTITUTION putting back together the original parts or elements RECUR happen again REFRACTORY not responding to treatment REGENERATION re-growth of a structure or of lost tissue REGIMEN pattern of giving treatment RELAPSE the return of a disease REMISSION disappearance of evidence of cancer or other disease RENAL pertaining to the kidneys REPLICABLE possible to duplicate RESECT remove or cut out surgically RETROSPECTIVE STUDY looking back over past experience

SARCOMA a type of cancer SEDATIVE a drug to calm or make less anxious SEMINOMA a type of testicular cancer (found in the male sex glands) SEQUENTIALLY in a row, in order SOMNOLENCE sleepiness SPIROMETER an instrument to measure the amount of air taken into and exhaled from the lungs STAGING an evaluation of the extent of the disease STANDARD OF CARE a treatment plan that the majority of the medical community would accept as appropriate STENOSIS narrowing of a duct, tube, or one of the blood vessels in the heart STOMATITIS mouth sores, inflammation of the mouth STRATIFY arrange in groups for analysis of results (e.g., stratify by age, sex, etc.) STUPOR stunned state in which it is difficult to get a response or the attention of the subject SUBCLAVIAN under the collarbone SUBCUTANEOUS under the skin SUPINE lying on the back SUPPORTIVE CARE general medical care aimed at symptoms, not intended to improve or cure underlying disease SYMPTOMATIC having symptoms SYNDROME a condition characterized by a set of symptoms SYSTOLIC top number in blood pressure; pressure during active contraction of the heart

TERATOGENIC capable of causing malformations in a fetus (developing baby still inside the mother’s body) TESTES/TESTICLES male sex glands THROMBOSIS clotting THROMBUS blood clot TID three times a day TITRATION a method for deciding on the strength of a drug or solution; gradually increasing the dose T-LYMPHOCYTES type of white blood cells TOPICAL on the surface TOPICAL ANESTHETIC applied to a certain area of the skin and reducing pain only in the area to which applied TOXICITY side effects or undesirable effects of a drug or treatment TRANSDERMAL through the skin TRANSIENTLY temporarily TRAUMA injury; wound TREADMILL walking machine used to test heart function

UPTAKE absorbing and taking in of a substance by living tissue

VALVULOPLASTY plastic repair of a valve, especially a heart valve VARICES enlarged veins VASOSPASM narrowing of the blood vessels VECTOR a carrier that can transmit disease-causing microorganisms (germs and viruses) VENIPUNCTURE needle stick, blood draw, entering the skin with a needle VERTICAL TRANSMISSION spread of disease

WBC white blood cell

IMAGES

  1. Do Plants Feel Pain: Eye-Opening Facts About Plants You Need To Know

    research on plants feeling pain

  2. Plants feel PAIN!

    research on plants feeling pain

  3. Do Plants Feel Pain? A Biochemical Perspective

    research on plants feeling pain

  4. Do Plants Feel Pain? Scientists Prove It With This Cool Expe

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  5. Do Plants Feel Pain? New Research Reveals the Unexpected Truth

    research on plants feeling pain

  6. Do plants feel pain? Some Interesting Facts to Know

    research on plants feeling pain

VIDEO

  1. Plants DO feel pain

  2. PLANTS DONT FEEL PAIN

  3. plants do feel pain

  4. PlAnTs DoNt FeEl pAiN

  5. plants do feel pain!

  6. Pain of plants #plants #pain

COMMENTS

  1. Anesthetics and plants: no pain, no brain, and therefore no consciousness

    They therefore cannot experience pain. Advocates of consciousness and cognition in plants point out, however, that plants react to damaging cues with widespread electrical and chemical signals, resembling a coordinated reaction (van Bel et al. 2014; Gallé et al. 2015 ). Plants do indeed respond to burning injuries and destructive wounding by ...

  2. A Group of Scientists Suggest that Plants Feel Pain

    A Group of Scientists Suggest that Plants Feel Pain. For years, scientists are baffled by the question of whether plants can feel pain or not. A team of scientists from Tel Aviv University may ...

  3. Do Plants Feel Pain? A Primer on Plant Neurobiology

    According to researchers at the Institute for Applied Physics at the University of Bonn in Germany, plants release gases that are the equivalent of crying out in pain. Using a laser-powered microphone, researchers have picked up sound waves produced by plants releasing gases when cut or injured. Although not audible to the human ear, the secret ...

  4. Debunking a myth: plant consciousness

    For instance, could research on genetically modified plants face even more resistance if plants were regarded as conscious? How might laboratory-research regulations be impacted when scientists are seen to perform invasive manipulations on plants that feel pain? ... Do plants feel pain? Disputatio. 2020; 12:71-98. doi: 10.2478/disp-2020-0003 ...

  5. (PDF) Do Plants Feel Pain?

    Abstract. Many people are attracted to the idea that plants experience phenomenal conscious states like pain, sensory awareness, or emotions like fear. If true, this would have wide-ranging moral ...

  6. Anesthetics and plants: no pain, no brain, and therefore no ...

    Plants have a rich variety of interactions with their environment, including adaptive responses mediated by electrical signaling. This has prompted claims that information processing in plants is similar to that in animals and, hence, that plants are conscious, intelligent organisms. In several recent reports, the facts that general anesthetics cause plants to lose their sensory responses and ...

  7. Anesthetics and plants: no pain, no brain, and therefore no

    Anesthetics and plants: no pain, no brain, and therefore no consciousness Protoplasma. 2021 Mar;258(2):239-248. doi: 10.1007/s00709-020-01550-9. ... The question therefore arises: do plants feel pain and have consciousness? In this review, we discuss what can be learned from the effects of anesthetics in plants. For this, we describe the ...

  8. Do Plants Feel Pain?

    Given that plants do not have pain receptors, nerves, or a brain, they do not feel pain as we members of the animal kingdom understand it. Uprooting a carrot or trimming a hedge is not a form of botanical torture, and you can bite into that apple without worry. However, it seems that many plants can perceive and communicate physical stimuli and ...

  9. Do Plants Feel Pain?

    Many people are attracted to the idea that plants experience phenomenal conscious states like pain, sensory awareness, or emotions like fear. If true, this would have wide-ranging moral implications for human behavior, including land development, farming, vegetarianism, and more. Determining whether plants have minds relies on the work of both empirical disciplines and philosophy. Epistemology ...

  10. PDF Do Plants Feel Pain?

    Do Plants Feel Pain? Adam Hamilton Independent researcher Justin McBrayer Fort Lewis College DOI: 10.2478/disp-2020-0003 BIBLID [0873-626X (2020) 56; pp.71-98] Abstract

  11. Do Plants Feel Pain? No, and Here's How Scientists Know

    In short, no. It's notoriously difficult to prove the non-existence of something, and doubly so when that thing is a subjective experience like pain. That said, almost everything we know about plants suggests that they aren't capable of feeling pain — or anything, for that matter. For one, plants don't have nociceptors, nervous systems ...

  12. Do Plants Feel Pain? What We Know About Plants' 'Distress Signal'

    The answer to whether plants feel pain is not straightforward, as they do not feel pain like us humans do, but some plant scientists posit that they may feel pain in their own way. One of the most ...

  13. Do Plants Feel Pain? Exploring the Science and Debate

    If plants could feel pain, it would impact how we treat them, from gardening to agriculture. ... While research continues, there's no clear consensus on whether plants experience conscious pain. The Ongoing Debate. The question of plant sentience raises fascinating ethical and philosophical discussions.

  14. Do Plants Really Feel Pain? What Does Science Say?

    Due to advancements in science, techniques such as Judgement Bias Testing (JBT) show that animals experience pain in a way similar to humans - not plants, as coverage of the "plants feel pain" study implies. What JBT does is measure an individual's "affective state," or emotional state through how they respond to ambiguous situations.

  15. The Intelligent Plant

    The Intelligent Plant. By Michael Pollan. December 15, 2013. Plants have electrical and chemical signalling systems, may possess memory, and exhibit brainy behavior in the absence of brains ...

  16. Plants can communicate and respond to touch. Does that mean they're

    Within two minutes, the whole plant had received a signal of my touch, of my "assault," so to speak, with these tweezers. And research like that is leading people within the plant sciences, but also people who work on neurobiology in people to question whether or not it's time to expand the notion of a nervous system. On if plants feel pain

  17. Do Plants Think?

    Plants exhibit elements of anoetic consciousness which doesn't include, in my understanding, the ability to think. Just as a plant can't suffer subjective pain in the absence of a brain, I ...

  18. Do Plants Feel Pain? A Biochemical Perspective

    However, the mechanisms behind intercellular communication in plants are complex and still largely unexplored, and there is much ongoing research examining how plants can respond to stimuli. Do plants feel pain as we perceive it? While we do have some idea of what happens internally when a plant is damaged, we cannot compare it to the way ...

  19. New research on plant intelligence may forever change how you think

    So what about pain? Do plants feel? Pollan says they do respond to anesthetics. "You can put a plant out with a human anesthetic. … And not only that, plants produce their own compounds that are anesthetic to us." But scientists are reluctant to go as far as to say they are responding to pain. How plants sense and react is still somewhat unknown.

  20. Do Plants Feel Pain?

    There is no evidence that plants have minds in the sense relevant for morality, and evidence for other minds comes either from testimony, behavior, anatomy/physiology, or phylogeny. Abstract Many people are attracted to the idea that plants experience phenomenal conscious states like pain, sensory awareness, or emotions like fear. If true, this would have wide-ranging moral implications for ...

  21. Plants Feel Pain and Might Even See

    You would think that plants experiencing pain and now the hypothesis that they might even be able to see would put the whole scientific community into a state of high excitement. The reaction, however, was muted. I had assumed that plant neurobiology was an up-and-coming scientific field. Baluška shook his head.

  22. Plants Really Do Respond to The Way We Touch Them ...

    It's something that plant lovers have long suspected, but now Australian scientists have found evidence that plants really can feel when we're touching them. Not only that, but different sensations trigger a cascade of physiological and genetic changes, depending on the stimulation the plants are receiving, whether it's a few drops of rain, or ...

  23. Do Plants Have Feelings? All Sides of the Debate

    Modern research that relies on human understanding of emotional reactions certainly concludes that plants don't feel pain or have any other feelings. Yet the debate is far from over. Regardless of what the final answer is, it wouldn't change the fact that a plant-based diet is the most plant-friendly nutritional choice you can make.

  24. Medical Terms in Lay Language

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