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Plants cannot “think and remember,” but there’s nothing stupid about them: They’re shockingly sophisticated

The views expressed are those of the author and are not necessarily those of Scientific American.


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New research shows that plants "can think and remember," according to a news story published this week.

Plants can transmit information "from leaf to leaf in a very similar way to our own nervous systems," BBC News wrote. The article continues to assert that plants remember information and use "information encrypted in the light to immunize themselves against seasonal pathogens."

Plants cannot think or remember. These borrowed terms do not accurately describe how plants function. However, like most organisms, plants can sense the world around them, process information from their environment, and respond to this information by altering their growth and development. In fact, plants respond to changes in their environment in ways that many would find surprisingly sophisticated, although botanists have known of these abilities for centuries.

"A big mistake people make is speaking as if plants ‘know’ what they’re doing," says Elizabeth Van Volkenburgh, a botanist at the University of Washington. "Biology teachers, researchers, students and lay people all make the same mistake. I’d much rather say a plant senses and responds, rather than the plant ‘knows.’ Using words like ‘intelligence’ or ‘think’ for plants is just wrong. Sometimes it’s fun to do, it’s a little provocative. But it’s just wrong. It’s easy to make the mistake of taking a word from another field and applying it to a plant."

The BBC News story is based on a study set for publication in The Plant Cell. Co-author Stanislaw Karpinski of the Warsaw University of Life Sciences in Poland recently presented his research at the annual meeting of the Society for Experimental Biology in Prague, Czech Republic.

The story maintains that, according to the study, stimulating one leaf cell with light creates a cascade of electrochemical events across the entire plant, communicated via specialized cells called bundle-sheath cells just as electrical impulses are propagated along the nerve cells in the nervous system of an animal. The researchers found that these reactions continued several hours later, even in the dark, which they interpreted to indicate a kind of memory.

This is like saying that because the surface of a pond continues to ripple once struck by a pebble, the water is "remembering" something. The analogy doesn’t quite hold. But plants do produce electrical signals and the function of these signals in response to light is the real focus of the new study—the most recent contribution to a growing body of work about electrical signaling in plants.

Although plants don’t have nerves, plants cells are capable of generating electrical impulses called action potentials, just as nerve cells in animals do. In fact, all biological cells are electrical.

Cells use membranes to keep their interiors separate from their exteriors. Some very tiny molecules can infiltrate the membranes, but most molecules must pass through pores or channels found within the membrane. One group of migratory molecules is the ion family: charged particles like sodium, potassium, chloride and calcium.

Whenever different concentrations of ions accumulate on opposite sides of a cell membrane, there exists the potential for an electrical current. Cells manage this electric potential using protein channels and pumps embedded in the cell membrane—gatekeepers that regulate the flow of charged particles across the cell membrane. The controlled flow of ions in and out of a cell constitutes electrical signaling in both plants and animals.

"In any cell you have a membrane," explains Alexander Volkov, a plant physiologist at Oakwood University in Alabama. "You have ions on both sides in different concentrations, which creates an electrical potential. It doesn’t matter if it’s an animal or plant cell—it’s general chemistry."

Because certain types of plant cells have some features in common with nerve cells—they are arranged in tubular bundles, they harbor ion channels in their membranes—some botanists have suggested that plants propagate action potentials along connected networks of these cells, akin to signaling in an animal’s nervous system. But most botanists agree that plants don’t have networks of cells that have evolved specifically for rapid electrical signaling across long distances, as most animals do. Plants simply don’t have true nervous systems.

So if plants aren’t using electrical signals in nervous systems like animals, what do they do with the electrical impulses they produce? In most cases, plant biologists don’t know. "We’ve known about electrical signaling in plants for as long as we’ve known about it in animals," says Van Volkenburgh. "But in most plants, what those signals are for is an open question." The notable exceptions to this mystery are plants that rely on electric signals for rapid movement, like the carnivorous Venus flytrap or Mimosa pudica—a plant whose leaves fold up when brushed to discourage herbivores (see movie below).

In recent years, some research has suggested that electrical signaling in plants modifies and regulates all kinds of biological processes in plant cells. Electrical signals, some botanists have argued, power more than the snapping traps of the exotic Venus flytrap—they are just as important for the grass growing on your lawn. Measuring electrical impulses in plants is easy, but linking them to specific plant functions is much more difficult and the plant biology community is nowhere near reaching a consensus about how most plants use those impulses.

Karpinski’s new study attempts to link light-activated electrical activity to immune defenses in plants. In the new study, researchers infected the leaves of Arabidopsis thaliana (thale cress) with a bacterial pathogen either one hour before exposing the plant to a strong dose of blue, red or white light or one, eight or 24 hours after exposing the plant to light. Plants treated with light before infection developed resistance, but plants infected without any preceding illumination showed no resistance.

When exposed to strong light, Karpinski explains, plants absorb more energy than they can use for photosynthesis—but he doesn’t think plants waste this excess energy. Karpinski says plants convert the energy to heat and electrochemical activity that can later trigger biological processes, like immune defenses. "It seems that plants can raise resistance against pathogens only using their light absorption system," Karpinski says. "We found that electrochemical signaling is regulating this process. Electrical signaling in plants is known from the time of Darwin—it is nothing new. But what was not described is that light can induce action potentials. We have found there is a different signaling for blue, white and red light. If plants can signal differently different wavelengths of light, then plants can see colors as well."

Karpinski thinks plants generate different electrical impulses when different wavelengths of light hit their leaves and that plants use these impulses to somehow regulate their immune defenses. He even speculates that plants can use this ability to battle seasonal pathogens. But exactly how this mechanism would work is unclear.

The role of electrical signaling in most plants remains largely mysterious and unexplained—and certainly does not warrant claims that plants can "think and remember." But there are plenty of well-documented examples of the sophisticated ways in which plants change their own growth in response to changes in their environment.

Just think about the fact that roots always grow in the direction of gravity and shoots always grow toward the light—even if you turn a plant on its side. Biologists have worked out that these processes, called gravitropism and phototropism respectively, rely on hormones that change the rate of cellular growth in plant tissues: If one side of a root or shoot is growing faster than another, it’s going to bend. Climbing plants, like vines and creepers, use similar mechanisms to respond to touch, clinging and curling around the first pole, wall, or branch they contact.

Plants also process information from their environment and change their growth based on that information. "Some plants flower as the days are getting shorter and others as the days are getting longer. They ‘know’ that the days are getting longer or shorter by having tabulated reactions to each day and night length," says Van Volkenburgh. "The way this works is based on the circadian rhythm of plants. People don’t realize plants have a circadian rhythm just like animals do. Plants have all kinds of movement based on their circadian rhythms."

Young sunflowers and other young plants’ flowering tops and leaves can trace the sun’s arc from East to West—a phenomenon called heliotropism that ensures maximum light exposure during a crucial period of growth. Then there are more startling examples of plants changing in response to their environment. Consider the Telegraph plant: a peculiar Asian shrub with tiny satellite leaves that constantly swivel to monitor the light in its environment. The satellite leaves pivot so dependably and swiftly that you can actually observe them moving in real time (see movie below). Their perpetual dance tracks the movement of light over the course of the day, adjusting the position of the primary leaves to absorb as much light as possible.

With such surprising examples of plants’ abilities to process information and adapt to their environments, there’s no need to try and endow plants with intelligence, thought, memory or other cognitive abilities they do not truly possess and do not need. They’re plenty smart already.

Image of leaf courtesy of Wikimedia Commons





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  1. 1. JamesDavis 9:37 pm 07/16/2010

    I am too dumb to know if a plant is smart, but I do know that some of them are very clever; consider the dandelion. I think I only have a few in my yard, so I will wait until those things get tall enough so I can cut those little yellow heads off with the lawnmower. The next morning, there are a thousand or more of them already up and most of them had already gone to seed. The ones I cut down the day before was a "sacrifice" I get the lawnmower again to cut the ones down that haven’t went to seed and when I look back to see if I got them all, the ones that hadn’t went to seed only grew high enough to miss the lawnmower blade. Some times I would swear on a stack of bibles that those dandelion that only grew high enough to miss the mower blade is laughing at me. Smart…I don’t know, but damn clever…yes.

    Link to this
  2. 2. BuzzCoastin 12:23 am 07/17/2010

    Since we really don’t understand the mechanisms of human thought or memory, it is neither incorrect nor correct to say that plants think and remember. The conclusion we might draw from the data at this point is: plants seem to exhibit traits that we would call cognitive when compared with the traits of human perception. And regrettably, I have known many people who seem less intelligent (less cognitively sophisticated) than plants.

    Possibly plants hold some clues as to how our thought process and memory process work.

    Link to this
  3. 3. dbtinc 8:54 am 07/17/2010

    I suspected that my geraniums were more intelligent than a number of politicians but I guess we get what we deserve …

    Link to this
  4. 4. jtdwyer 7:31 pm 07/17/2010

    While my old memory fails me and I’m too tired to do any research, I watched an interesting documentary a year or so ago about antelopes dying in some fenced in African reserves, but not others. It turns out they were being poisoned by the shrubbery. Once this particular type of plant had been overgrazed by the antelopes, it released a chemical compound into the atmosphere, signaling other plants to increase their production of toxins. Antelopes in reserves with overgrazed plants died those. So in some sense plants may not only think and learn but communicate.

    Since plants don’t usually move much, their internal clocks may be much slower than animals’. Plans most often move by preferential growth. New roots are directed towards the immediate area of grater moisture, only when they are growing, when water and nutrients are available, which can cause plants to ‘move’ towards the banks of streams, for example.

    But what do they really know? It’s probably all just their imagination…

    Link to this
  5. 5. ultimobo 10:34 pm 07/17/2010

    I walk past a park gazebo with I think Wisteria vine tendrils waving in the breeze. I note that if they find and contact something solid, then they will wind around and capture that – otherwise they will wither. Looks kindof intelligent to me.

    Link to this
  6. 6. stan_39 1:19 am 07/18/2010

    A big mistake is when botanist-physiologists disuse molecular, biophysical and physiological data without reading and understanding the experiments described in the Plant Cell (www.plantcell.org/cgi/doi/10.1105/tpc.109.069302). In other words Elisabeth van Volkenburgh expressed opinion that was not rooted in the experimental facts presented by the researchers from the Warsaw University of Life Sciences.
    Definition of thinking: Representative reactions towards stimuli from internal chemical reactions or external environmental factors (this definition precludes the notion that anything inorganic could ever be made to "think.
    It is written in TPC article: A definition of memory and intelligence for plants was proposed by Trewavas (2003): adaptively variable growth and development during the lifetime of the individual. In animals, memory is connected with intelligence in such a way; the more intelligent the organism is, the greater the degree of individual adaptively variable behavior. Because this definition was used to describe intelligence in other organisms than humans, we used this definition in our experimental system. Do plants exhibit memory and behavior that result from memorized previous events? Our data (Figures 6 and 7; see Supplemental Figure 4 online) indicate that plants possess memory of previous light incidents, hereafter called cellular light memory, which is used for optimization of future light acclimatory and immune defense responses. In other words, plants can store and use information from the spectral composition of light to anticipate changes that might appear in the near future in the environment, for example, for anticipation of pathogen attack (Figures 6 and 7). Therefore, plants have to possess a mechanism for processing of the memorized information.

    Accordingly to the above definitions plant leaves, cells, can perform thinking and specifically memorize different light incidents. This is a scientific fact not an opinion.

    The same is concerning comments made by Alexander Volcov. In TPC paper are presented experimental evidences, that not any cell in plants can systemicly transduce photoelectrophysiological signaling, but the bundle sheath cells of the vienal tissues are able to do it.

    Sincerely,

    Stanislaw Karpinski

    Link to this
  7. 7. jtdwyer 2:09 am 07/18/2010

    stan_39 – Your research looks to my casual perusal to be very interesting. I guess you may be on to significant discovery and wish you well.

    As an old information systems analyst, it’s interesting to me that physicists consider the state of elementary particle characteristic properties to be ‘quantum information’. I have some objection to their casual borrowing of terms and loose misapplication of concepts, but there is some valid (and invalid) usage.

    Conceptually, even the structural characteristics of cellular organisms can in some sense be considered memory. Your experimental evidence that plants utilize the energy of excess light exposure for information processing is very interesting. While we rush to make electronic processes that cycle at extraordinary rates, plants have little need to process information so quickly. Without going so far as to speculate about conscious self awareness (avoiding corrective treatment), the cellular mass of collective plant material has a tremendous potential for information storage and processing, perhaps at rates we cannot perceive. But that’s carrying things too far. Again, good luck in your research, but watch your speed!

    By the way, I think your assessment of non-organic intelligence fails to appreciate the potential of electromechanical chemical receptors, etc. Unfortunately, I think there’s little that can be accomplished (by nature) with biochemistry that may not be someday achieved with electronics based technology, given adequately capable designers.

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  8. 8. christophermark 8:54 am 07/18/2010

    Several species of passionflower in Central America have developed cyst-like bumps on their leaves that mimic the size, color and shape of a hatch of butterfly eggs. The tiny cysts, in the form of dummy eggs, confuses all egg-bearing butterflies of the offending species, giving the impression that the plants territory is occupied, and since the host cannot support two hatches of larvae, butterflies bearing eggs, seeing it, pass on in search of greener pastures. Most mimicry involves similarity of appearance. Further investigations have disclosed cases of orchids in which smell, behavior, and even biochemistry is mimicked. An unanswered question: how does the passionflower, for example, know the size, color and shape of a hatch of butterfly eggs? (cf. 1995 Attenborough, D., The Private Lives of Plants, BBC Books, London, p. 66-67;cf also 124-131 and Mimicry/Defensive egg dummies, Britannica CD 2000 Deluxe Edition, 1999-2000. Encyclopdia Britannica, Inc.)

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  9. 9. christophermark 9:26 am 07/18/2010

    Several species of passionflower in Central America are said to have developed tiny cyst-like bumps on their leaves that mimic the size, color and shape of a hatch of butterfly eggs. The “cysts”, in the form of “dummy” eggs, confuse the egg-bearing butterflies of the offending species, giving the impression that the plant’s territory is “occupied”, and since the host cannot support two hatches of larvae, butterflies bearing eggs pass on in search of greener pastures. There is the also case 36 orchid species that mimic the biochemistry of female pheromones in 36 species of bees. The unanswered question: how does the passionflower “know” the size, color and shape of a hatch of butterfly eggs? In the case of the orchid, how does it “know” the biochemistry of female sex pheromone of a particular species of bee thereby attracting the male of that species to pollinate it? As for the thirty-five other species of orchids, they similarly attract thirty-five other species of bees, each orchid attracting a single species of bee by mimicking its sexual pheromone. (cf. 1995 Attenborough, D., The Private Lives of Plants, BBC Books, London, p. 66-67;cf also 124-131 and “Mimicry”/”Defensive egg dummies”, Britannica© CD 2000 Deluxe Edition, 1999-2000. Encyclopædia Britannica, Inc.) Would greatly appreciate anyone with links, comments, etc. that further illuminate these examples.

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  10. 10. jtdwyer 10:50 am 07/18/2010

    christophermark – I was going to pass along Carl Sagan’s story in the Cosmos Series about crabs in Japan that have the remarkable appearance of a stylized Japanese Samurai on the back of their shell, artificially selected by Japanese crab fishermen throwing them back, but it turn out to be a myth, unless fossils of these crabs had been selected by early hominids. Its an interesting anti-mimicry adjunct, though:
    http://crustacea.nhm.org/people/martin/publications/pdf/103.pdf

    An interesting experiment might determine how many tens of thousands or millions of years it takes for orchids to mimic a new bee species’ pheromones.

    Interesting that your examples all involve flowering plants and interdependent insect species. Any possibility that the bees are also cooperating by tuning their pheromones to orchid scents? Just an idle thought…

    Link to this
  11. 11. zstansfi 11:53 pm 07/18/2010

    It’s clearly important to point out that any term when defined in a particular manner can be used in a variety of ways. While undoubtedly the authors of this paper have shown that specific plants may react in a manner that fits their chosen definition of ‘thought’ or ‘intelligence’, it is also clear that those terms are often defined much differently in the animal literature. Thus, when based on a more traditional definition of intelligence or thought, such terms are not accurate descriptions of any physiological process that occurs in these plant (so far as we know).

    On the other hand, the ever-widening definition of ‘memory’ – which is often now equated with rapid structural changes at the synaptic level – very likely does encompass the process that the authors describe in the article. In particular, the study shows the development of long-term (over several hours or days) adaptations to environmental stressors (i.e. harmful pathogens) following stimulus presentation (i.e. a particular wave-length of light). This could easily fit into a definition of ‘memory’ used within the animal literature.

    That said, it appears as though the primary issue being contested in this instance is the characterization of this study in the media. In particular, the BBC article quotes a researcher unaffiliated with the study as stating that this sort of adaptation "requires an appraisal of the situation and an appropriate response – that’s a form of intelligence". While this statement may accurately describe intelligence, it is inaccurate to state that these results demonstrate anything like an ‘appraisal’ occurring in the plants. Moreover, considering the lay definition of intelligence, it is not difficult to see how such an unqualified characterization of these results would appear as nothing more than an absurd analogy taken to the extreme.

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  12. 12. jtdwyer 1:46 am 07/19/2010

    zstansfi – Human language in general and the specific terminology of psychology and other sciences have been developed to describe our perceptions of and conceptions about human intellect. This language has been adopted and adapted over more than a hundred years to apply to animals and more recently electronic computers. Any discovery of information processing in plants should not be dismissed because it doesn’t easily fit within the context our existing conceptions of intelligence.

    Any system that employs accumulated information to direct current or future actions must be considered an information processing system regardless of is storage mediums or processing methods; whether its processing cycle time is nanoseconds or years.

    If any new conception of plant information processing cannot be fit within existing terminology established by scientific disciplines, then some new terminology must be negotiated to extend our current level of understanding.

    If the world’s biomass has any information to pass along to us, even if it is merely perhaps a recording of environmental conditions, it would be foolish for us to ignore it.

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  13. 13. christophermark 5:46 am 07/19/2010

    Thanks JT; All three of your comments deserve careful consideration. Interestingly, Darwin himself uses the term ‘contrivances’ for manifold deceits orchids use to get themselves pollinated; Attenborough prefers the verb ‘bamboozle’ – both imply a certain complexity and ‘working out’ a way ahead for an apparent purpose (e.g. survival). Yes, both scientists are subject to charges of enlisting anthropocentric thought forms and levying them onto plants, but bear in mind both are practiced communicators who ordinarily choose their words very carefully. Another evolution scenario would have the female butterfly ‘realize’ she is being bamboozled and lay her eggs anyway, or, in your example, that the female bee ‘realizes’ that by mimicking an orchid scent she has decreased her chances of being (no pun intended) fertilized for she is now in competition with an orchid. In any case, two ‘problems’ confront us on separate levels: the apparent complexity of the relationship between plant and insect on the one hand and the danger of glossing over such anomalies for the sake of staying on the sweet, narrow and straight path of evolution theory, believing that in its present form it can explain everything.

    Link to this
  14. 14. jtdwyer 7:27 am 07/19/2010

    christophermark – Thanks for your thoughtful consideration. In my case its always more appropriate to assume that nothing is completely understood.

    Link to this
  15. 15. stan_39 8:29 am 07/19/2010

    Some researchers think that, scientific terms like memory, thinking and nerve system is exclusively reserved for humans and maybe for some higher animals. Let them think like that. Einstein was also thinking that the Universe is static and homogenous and did not accept the finding of escape of galaxies made by Hubble not mention the black energy and matter. Time has verified his mistake. We are not animal neurophysiologists but we are molecular physiologists and biophysicists and we can our job very well. Moreover the article went through the tuff peer review process in the Plant Cell.

    The peculiar future of the some critical comments concerning the memory, thinking and nerve system in plants is that the interlocutors express their opinion without prior knowledge what was presented in The Society of Experimental Biologists annual general meeting in Prague and what was published in the Plant Cell article. This is very serious mistake of Ferris Jabr and selected by her some researchers that comment (I do not know what). This is typical cowboys attitude shoot first ask questions later I am sure that Ferris Jabr wrote this opinion article before interviewing me and before reading the Plant Cell article. I advice to see:

    http://www.popsci.com/science/article/2010-07/study-unveils-plant-nervous-system-illuminating-how-plants-remember-and-react,

    which present objectively the finding we did. Because Ferris Jabr wrote that Plants cannot think and remember and they do not have nerve system they certainly cannot and dont!
    Let it be….

    Link to this
  16. 16. jaytudu 7:10 am 07/20/2010

    I have one very basic question, is the same experiment produce same reponses for the dead plant (plant which is separated from the root) also. I am just interested to see the difference between dead plan and living plant.

    Thank you

    Link to this
  17. 17. tiurlumphd 2:38 am 07/22/2010

    amazing progress report about plants,leaves, roots etc.keep up the discovery series guys…

    Link to this
  18. 18. Buu 11:28 pm 08/5/2010

    Last time I piss in a bush.

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  19. 19. britt1915 6:42 pm 09/12/2010

    No one would ever think that plants could absorb information around them. They are also smart because plants have evolved like humans did so and survived as well. In order for plants to have survived over the centuries they had to learn about their environment and gather information in order to understand what is going on around them. Also along with learning plants DNA changes over time and gets passed to their offspring so they can survive. However even though plants do not think they do learn which makes them very smart. Another way plants are smart is they have the ability to battle pathogens that harm them by raising their resistance to them like humans. This is considered very smart because plants are able to survive. If plants did not have this ability they really wouldnt be so smart because they would be dead. Plants are a bit like humans because they learn from their surroundings and can change in order to adjust to what is happening to them.

    Link to this
  20. 20. 411314 8:48 am 09/17/2010

    "While my old memory fails me and I’m too tired to do any research, I watched an interesting documentary a year or so ago about antelopes dying in some fenced in African reserves, but not others. It turns out they were being poisoned by the shrubbery. Once this particular type of plant had been overgrazed by the antelopes, it released a chemical compound into the atmosphere, signaling other plants to increase their production of toxins. Antelopes in reserves with overgrazed plants died those. So in some sense plants may not only think and learn but communicate.

    Since plants don’t usually move much, their internal clocks may be much slower than animals’. Plans most often move by preferential growth. New roots are directed towards the immediate area of grater moisture, only when they are growing, when water and nutrients are available, which can cause plants to ‘move’ towards the banks of streams, for example.

    But what do they really know? It’s probably all just their imagination…"

    I’m pretty sure you’re making the same mistake Karpinski did, misinterpreting plants’ ability to react to their environment as evidence of sentience.

    Link to this
  21. 21. 411314 8:59 am 09/17/2010

    They referred to things mentioned in the article you linked to (for example, the fact that shining a light on a plant causes a cascade of electrical events all along the plant), so I’m pretty sure they DID read it.

    Link to this
  22. 22. 411314 1:42 pm 09/17/2010

    Your story actually seems like further evidence of the article’s point. If the plants were self-aware, why is it they didn’t poison the antelope untill after they’d been overgrazed? That would mean that untill the grazing reached a certain limit, some of the plants allowed themselves to be eaten! Would you allow an animal to eat you so long as they hadn’t "overeaten" the local human population? Do you think animals woud let you shoot them so long as you weren’t killing to many of them in too short a time?

    I don’t know how the signaling or the always growing into moistest areas things work, but just because one doesn’t know the answer to something isn’t a good reason to assume the least likely explanation.

    Link to this

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