Plant cognition or plant gnosophysiology is the study of the
mental capacities of
plant
Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclud ...
s. It explores the idea that plants are capable of responding to and learning from stimuli in their surroundings in order to choose and make decisions that are most appropriate to ensure survival. Over recent years, experimental evidence for the cognitive nature of plants has grown rapidly and has revealed the extent to which plants can use senses and cognition to respond to their environments. Some researchers claim that plants process information in similar ways as animal
nervous system
In biology, the nervous system is the highly complex part of an animal that coordinates its actions and sensory information by transmitting signals to and from different parts of its body. The nervous system detects environmental changes th ...
s.
History
The idea of cognition in plants was first explored by
Charles Darwin
Charles Robert Darwin ( ; 12 February 1809 – 19 April 1882) was an English naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all species of life have descended fr ...
in the late 1800s in the book ''
The Power of Movement in Plants
''The Power of Movement in Plants'' is a book by Charles Darwin on phototropism and other types of movement in plants. This book continues his work in producing evidence for his theory of natural selection. As it was one of his last books, fol ...
'', co-authored with his son Francis. Using a neurological metaphor, he described the sensitivity of plant roots in proposing that the tip of roots acts like the
brain
A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a v ...
of some lower animals. This involves reacting to sensation in order to determine their next movement even though plants possess neither brains nor nerves.
Irrespective of whether this neurological metaphor is correct or, more generally, the modern application of
neuroscience
Neuroscience is the scientific study of the nervous system (the brain, spinal cord, and peripheral nervous system), its functions and disorders. It is a multidisciplinary science that combines physiology, anatomy, molecular biology, development ...
terminology and concepts to plants is appropriate, the Darwinian idea of the
root tip of plants functioning as a "brain-like" organ (together with the so-called "
root
In vascular plants, the roots are the organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often below the sur ...
-
brain
A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a v ...
hypothesis") has experienced an ongoing revival in
plant physiology
Plant physiology is a subdiscipline of botany concerned with the functioning, or physiology, of plants. Closely related fields include plant morphology (structure of plants), plant ecology (interactions with the environment), phytochemistry (bi ...
.
While plant "
neurobiology
Neuroscience is the scientific study of the nervous system (the brain, spinal cord, and peripheral nervous system), its functions and disorders. It is a multidisciplinary science that combines physiology, anatomy, molecular biology, development ...
" focuses on the physiological study of plants, modern plant cognition primarily applies a
behavioural
Behavior (American English) or behaviour (British English) is the range of actions and mannerisms made by individuals, organisms, systems or artificial entities in some environment. These systems can include other systems or organisms as wel ...
/ecological approach. Today, plant cognition is emerging as a field of research directed at experimentally testing the cognitive abilities of plants, including
perception
Perception () is the organization, identification, and interpretation of sensory information in order to represent and understand the presented information or environment. All perception involves signals that go through the nervous system ...
,
learning
Learning is the process of acquiring new understanding, knowledge, behaviors, skills, value (personal and cultural), values, attitudes, and preferences. The ability to learn is possessed by humans, animals, and some machine learning, machines ...
processes,
memory
Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If past events could not be remembered, ...
and
consciousness
Consciousness, at its simplest, is sentience and awareness of internal and external existence. However, the lack of definitions has led to millennia of analyses, explanations and debates by philosophers, theologians, linguisticians, and scien ...
. This framework holds considerable implications for the way we perceive plants as it redefines the traditionally held boundary between animals and plants.
Types
The study of plant cognition stems from the idea that plants are able to learn and adapt to their environment with only a
stimulus
A stimulus is something that causes a physiological response. It may refer to:
*Stimulation
**Stimulus (physiology), something external that influences an activity
**Stimulus (psychology), a concept in behaviorism and perception
*Stimulus (economi ...
, integration, and response system. While proven that plants do indeed lack a brain and the function of a conscious working nervous system, plants are still somehow capable of adapting to their environment and changing the integration pathway that would ultimately lead to how a plant “decides” to take response to a presented stimulus.
This raises issues of plant intelligence which is defined to be able to actively adapt to any stimulus presented to the species from the environment. Plants are therefore clever in sensing the environmental stimulus e.g young sunflowers that face the sun for their growth.
Plant memory
In a study done by
Monica Gagliano from the University of Western Australia’s Centre for Evolutionary Biology, ''
Mimosa pudica
''Mimosa pudica'' (from la, pudica "shy, bashful or shrinking"; also called sensitive plant, sleepy plant, action plant, touch-me-not, shameplant) is a creeping annual or perennial flowering plant of the pea/legume family Fabaceae. It is often g ...
'' (sensitive plant) was tested for habituation to repeatedly being dropped. After multiple drops, it was found that the plants eventually became habituated, opening their leaves more quickly compared to the first time they were dropped. While the mechanism of this plant behavior is still not fully understood, it is strongly linked to changes in the flux within
calcium channel
A calcium channel is an ion channel which shows selective permeability to calcium ions. It is sometimes synonymous with voltage-gated calcium channel, although there are also ligand-gated calcium channels.
Comparison tables
The following tables e ...
s.
Another example of short term "memory" of a plant is found in the
Venus flytrap
The Venus flytrap (''Dionaea muscipula'') is a carnivorous plant native to subtropical wetlands on the East Coast of the United States in North Carolina and South Carolina. It catches its prey—chiefly insects and arachnids—with a trapping ...
, whose rapid closure is only triggered when at least two trap hairs are contacted within twenty seconds of one another. One hypothesis that explains how this occurs is by electrical signalling in plants. When one trap hair (mechanoreceptor) is triggered, a sub-threshold potential is reached. When two trap hairs are triggered, a threshold is reached, generating an action potential that closes the trap.
Associative learning
In 2016, a research team led by Monica Gagliano set out to test whether plants learn to respond to predicted events in their environment. The research demonstrated that plants were capable of
learning the association between the occurrence of one event and the anticipation of another event (i.e.
Pavlovian learning).
By experimentally demonstrating associative learning in plants, this finding qualified plants as proper subjects of cognitive research.
In this study,
pea
The pea is most commonly the small spherical seed or the seed-pod of the flowering plant species ''Pisum sativum''. Each pod contains several peas, which can be green or yellow. Botanically, pea pods are fruit, since they contain seeds and d ...
plants were exposed to two different stimulus and were hypothesized that plants have the capability to associate one type of stimulus with another. One of these stimuli were exposing the pea plants to wind + light and the other plant being exposed to wind without light for the training phase. Once in the experimental phase, the plants were exposed only to the wind stimulus to observe the response the pea plants exhibit.
By the end of the experiment, the pea plants exposed to wind + light "learned" to associate wind with the presence of light, thus exhibiting growth towards the wind stimulus. On the other hand, pea plants exposed to wind without light exhibited growth away from the wind stimulus. The mechanism for this behavior isn't entirely understood, though it is hypothesized that this may have something to do with mechanoreceptors integrating with
photoreceptors within the plants. This explains why a non-light source would trigger a growth response in the trained pea plant that is commonly reserved for photoreceptors.
A replication study with a larger sample size, published in 2020, found no evidence of associative learning in pea plants. However, it also failed to replicate the finding that light functioned effectively as an unconditioned stimulus. Pea plants in this study displayed only a slight trend rather than a reliable directional growth response towards previously presented light. The replicated experimental setup differed from the original in the presence of higher levels of ambient and reflected light, which may have randomised directional growth somewhat and prevented replication.
Further research
In 2003,
Anthony Trewavas
Anthony James Trewavas (born 1939) FRS FRSE is Emeritus Professor in the School of Biological Sciences of the University of Edinburgh best known for his research in the fields of plant physiology and molecular biology. His research investig ...
led a study to see how the roots interact with one another and study their signal transduction methods. He was able to draw similarities between
water stress
Water scarcity (closely related to water stress or water crisis) is the lack of fresh water resources to meet the standard water demand. There are two types of water scarcity: physical or economic water scarcity. Physical water scarcity is where ...
signals in plants affecting developmental changes and
signal transduction
Signal transduction is the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events, most commonly protein phosphorylation catalyzed by protein kinases, which ultimately results in a cellula ...
s in
neural network
A neural network is a network or circuit of biological neurons, or, in a modern sense, an artificial neural network, composed of artificial neurons or nodes. Thus, a neural network is either a biological neural network, made up of biological ...
s causing responses in muscle. Particularly, when plants are under water stress, there are
abscisic acid
Abscisic acid (ABA) is a plant hormone. ABA functions in many plant developmental processes, including seed and bud dormancy, the control of organ size and stomatal closure. It is especially important for plants in the response to environmental s ...
dependent and independent effects on development. This brings to light further possibilities of plant decision-making based on its environmental stresses. The integration of multiple chemical interactions show evidence of the complexity in these root systems.
In 2012,
Paco Calvo Garzón and
Fred Keijzer speculated that plants exhibited structures equivalent to (1)
action potential
An action potential occurs when the membrane potential of a specific cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells, ...
s (2)
neurotransmitter
A neurotransmitter is a signaling molecule secreted by a neuron to affect another cell across a synapse. The cell receiving the signal, any main body part or target cell, may be another neuron, but could also be a gland or muscle cell.
Neuro ...
s and (3)
synapse
In the nervous system, a synapse is a structure that permits a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron or to the target effector cell.
Synapses are essential to the transmission of nervous impulses from ...
s. Also, they stated that a large part of plant activity takes place underground, and that the notion of a 'root brain' was first mooted by Charles Darwin in 1880. Free movement was not necessarily a criterion of cognition, they held. The authors gave five conditions of minimal cognition in living beings, and concluded that 'plants are cognitive in a minimal, embodied sense that also applies to many animals and even bacteria.'
In 2017 biologists from University of Birmingham announced that they found a "decision-making center" in the
root tip of dormant ''
Arabidopsis
''Arabidopsis'' (rockcress) is a genus in the family Brassicaceae. They are small flowering plants related to cabbage and mustard. This genus is of great interest since it contains thale cress (''Arabidopsis thaliana''), one of the model organi ...
'' seeds.
In 2014, Anthony Trewavas released a book called ''Plant Behavior and Intelligence'' that highlighted a plant's cognition through its colonial-organization skills reflecting insect swarm behaviors. This organizational skill reflects the plant's ability to interact with its surroundings to improve its survivability, and a plant's ability to identify exterior factors. Evidence of the plant's minimal cognition of spatial awareness can be seen in their root allocation relative to neighboring plants. The organization of these roots have been found to originate from the root tip of plants.
On the other hand, Dr. Crisp and his colleagues proposed a different view on plant memory in their review: plant memory could be advantageous under recurring and predictable stress; however, resetting or forgetting about the brief period of stress may be more beneficial for plants to grow as soon as the desirable condition returns.
Affifi (2018) proposed an empirical approach to examining the ways plants model coordinate goal-based behaviour to environmental
contingency as a way of understanding plant learning. According to this author,
associative learning
Learning is the process of acquiring new understanding, knowledge, behaviors, skills, values, attitudes, and preferences. The ability to learn is possessed by humans, animals, and some machines; there is also evidence for some kind of learnin ...
will only demonstrate
intelligence
Intelligence has been defined in many ways: the capacity for abstraction, logic, understanding, self-awareness, learning, emotional knowledge, reasoning, planning, creativity, critical thinking, and problem-solving. More generally, it can b ...
if it is seen as part of
teleological
Teleology (from and )Partridge, Eric. 1977''Origins: A Short Etymological Dictionary of Modern English'' London: Routledge, p. 4187. or finalityDubray, Charles. 2020 912Teleology" In ''The Catholic Encyclopedia'' 14. New York: Robert Appleton ...
ly integrated activity. Otherwise, it can be reduced to
mechanistic
The mechanical philosophy is a form of natural philosophy which compares the universe to a large-scale mechanism (i.e. a machine). The mechanical philosophy is associated with the scientific revolution of early modern Europe. One of the first expo ...
explanation.
Raja et al (2020) found that potted French bean plants, when planted 30 centimetres from a garden cane, would adjust their growth patterns to enable themselves to use the cane as a support in the future. Raja later stated that "If the movement of plants is controlled and affected by objects in their vicinity, then we are talking about more complex behaviours (rather than simple) reactions". Raja proposed that researchers should look for corresponding cognitive signatures.
In 2017 Yokawa, K. et al. found that, when exposed to anesthetics, a number of plants lost both their autonomous and touch-induced movements. Venus flytraps no longer generate electrical signals and their traps remain open when trigger hairs were touched, and growing pea tendrils stopped their autonomous movements and were immobilized in a curled shape.
Criticism
The idea of plant cognition is a source of controversy.
Amadeo Alpi and 35 other scientists published an article in 2007 titled “Plant Neurobiology: No brain, No gain?” in ''
Trends in Plant Science
''Trends in Plant Science'' is a peer-reviewed scientific journal published by Elsevier.
Abstracting and indexing
The journal is abstracted and indexed in:
*Science Citation Index Expanded
*Scopus
*Chemical Abstracts
* Embase
*MEDLINE
According ...
''.
In this article, they argue that since there is no evidence for the presence of
neuron
A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. N ...
s in plants, the idea of plant neurobiology and cognition is unfounded and needs to be redefined. In response to this article, Francisco Calvo Garzón published an article in ''Plant Signaling and Behavior''.
He states that, while plants do not have "neurons" as animals do, they do possess an information-processing system composed of cells. He argues that this system can be used as a basis for discussing the cognitive abilities of plants.
See also
* ''
Boquila trifoliolata''
*
Embodied cognition
Embodied cognition is the theory that many features of cognition, whether human or otherwise, are shaped by aspects of an organism's entire body. Sensory and motor systems are seen as fundamentally integrated with cognitive processing. The cognit ...
*
Plant perception (physiology)
Plant perception is the ability of plants to sense and respond to the environment by adjusting their morphology and physiology. Botanical research has revealed that plants are capable of reacting to a broad range of stimuli, including chemicals ...
*
Plantoid A plantoid is a robot or synthetic biology, synthetic organism designed to look, act and grow like a plant. The concept was first scientifically published in 2010 (although models of comparable systems controlled by neural networks date back to 2003 ...
References
Further reading
*
{{refend
Enactive cognition
Plant communication