Plant perception is the ability of plants to sense and respond to the environment by adjusting their morphology and physiology. [1] Botanical research has revealed that plants are capable of reacting to a broad range of stimuli, including chemicals, gravity, light, moisture, infections, temperature, oxygen and carbon dioxide concentrations, parasite infestation, disease, physical disruption, sound, [2] [3] [4] [5] and touch. The scientific study of plant perception is informed by numerous disciplines, such as plant physiology, ecology, and molecular biology.
Many plant organs contain photoreceptors (phototropins, cryptochromes, and phytochromes), each of which reacts very specifically to certain wavelengths of light. [6] These light sensors tell the plant if it is day or night, how long the day is, how much light is available, and where the light is coming from. Shoots generally grow towards light, while roots grow away from it, responses known as phototropism and skototropism, respectively. They are brought about by light-sensitive pigments like phototropins and phytochromes and the plant hormone auxin. [7]
Many plants exhibit certain behaviors at specific times of the day; for example, flowers that open only in the mornings. Plants keep track of the time of day with a circadian clock. [6] This internal clock is synchronized with solar time every day using sunlight, temperature, and other cues, similar to the biological clocks present in other organisms. The internal clock coupled with the ability to perceive light also allows plants to measure the time of the day and so determine the season of the year. This is how many plants know when to flower (see photoperiodism). [6] The seeds of many plants sprout only after they are exposed to light. This response is carried out by phytochrome signalling. Plants are also able to sense the quality of light and respond appropriately. For example, in low light conditions, plants produce more photosynthetic pigments. If the light is very bright or if the levels of harmful ultraviolet radiation increase, plants produce more of their protective pigments that act as sunscreens. [8]
Studies on the vine Boquila trifoliata has raised questions on the mode by which they are able to perceive and mimic the shape of the leaves of the plant upon which they climb. Experiments have shown that they even mimic the shape of plastic leaves when trained on them. [9] Suggestions have even been made that plants might have a form of vision. [10]
To orient themselves correctly, plants must be able to sense the direction of gravity. The subsequent response is known as gravitropism.
In roots, gravity is sensed and translated in the root tip, which then grows by elongating in the direction of gravity. In shoots, growth occurs in the opposite direction, a phenomenon known as negative gravitropism. [11] Poplar stems can detect reorientation and inclination (equilibrioception) through gravitropism. [12]
At the root tip, amyloplasts containing starch granules fall in the direction of gravity. This weight activates secondary receptors, which signal to the plant the direction of the gravitational pull. After this occurs, auxin is redistributed through polar auxin transport and differential growth towards gravity begins. In the shoots, auxin redistribution occurs in a way to produce differential growth away from gravity.
For perception to occur, the plant often must be able to sense, perceive, and translate the direction of gravity. Without gravity, proper orientation will not occur and the plant will not effectively grow. The root will not be able to uptake nutrients or water, and the shoot will not grow towards the sky to maximize photosynthesis. [13]
All plants are able to sense touch. [14] Thigmotropism is directional movement that occurs in plants responding to physical touch. [15] Climbing plants, such as tomatoes, exhibit thigmotropism, allowing them to curl around objects. These responses are generally slow (on the order of multiple hours), and can best be observed with time-lapse cinematography, but rapid movements can occur as well. For example, the so-called "sensitive plant" ( Mimosa pudica ) responds to even the slightest physical touch by quickly folding its thin pinnate leaves such that they point downwards, [16] and carnivorous plants such as the Venus flytrap (Dionaea muscipula) produce specialized leaf structures that snap shut when touched or landed upon by insects. In the Venus flytrap, touch is detected by cilia lining the inside of the specialized leaves, which generate an action potential that stimulates motor cells and causes movement to occur. [17]
Wounded or infected plants produce distinctive volatile odors, (e.g. methyl jasmonate, methyl salicylate, green leaf volatiles), which can in turn be perceived by neighboring plants. [18] [19] Plants detecting these sorts of volatile signals often respond by increasing their chemical defences and/or prepare for attack by producing chemicals which defend against insects or attract insect predators. [18]
Plants upregulate chemical defenses such as glucosinolate and anthocyanin in response to vibrations created during herbivory. [20]
Plants systematically use hormonal signalling pathways to coordinate their development and morphology.
Plants produce several signal molecules usually associated with animal nervous systems, such as glutamate, GABA, acetylcholine, melatonin, and serotonin. [21] They may also use ATP, NO, and ROS for signaling in similar ways as animals do. [22]
Plants have a variety of methods of delivering electrical signals. The four commonly recognized propagation methods include action potentials (APs), variation potentials (VPs), local electric potentials (LEPs), and systemic potentials (SPs) [23] [24] [25]
Although plant cells are not neurons, they can be electrically excitable and can display rapid electrical responses in the form of APs to environmental stimuli. APs allow for the movement of signaling ions and molecules from the pre-potential cell to the post-potential cell(s). These electrophysiological signals are constituted by gradient fluxes of ions such as H+, K+, Cl−, Na+, and Ca2+ but it is also thought that other electrically charge ions such as Fe3+, Al3+, Mg2+, Zn2+, Mn2+, and Hg2+ may also play a role in downstream outputs. [26] The maintenance of each ions electrochemical gradient is vital in the health of the cell in that if the cell would ever reach equilibrium with its environment, it is dead. [27] [28] This dead state can be due to a variety of reasons such as ion channel blocking or membrane puncturing.
These electrophysiological ions bind to receptors on the receiving cell causing downstream effects result from one or a combination of molecules present. This means of transferring information and activating physiological responses via a signaling molecule system has been found to be faster and more frequent in the presence of APs. [26]
These action potentials can influence processes such as actin-based cytoplasmic streaming, plant organ movements, wound responses, respiration, photosynthesis, and flowering. [29] [30] [31] [32] These electrical responses can cause the synthesis of numerous organic molecules, including ones that act as neuroactive substances in other organisms such as calcium ions. [33]
The ion flux across cells also influence the movement of other molecules and solutes. This changes the osmotic gradient of the cell, resulting in changes to turgor pressure in plant cells by water and solute flux across cell membranes. These variations are vital for nutrient uptake, growth, many types of movements (tropisms and nastic movements) among other basic plant physiology and behavior. [34] [35] (Higinbotham 1973; Scott 2008; Segal 2016).
Thus, plants achieve behavioural responses in environmental, communicative, and ecological contexts.
Plant behavior is mediated by phytochromes, kinins, hormones, antibiotic or other chemical release, changes of water and chemical transport, and other means.
Plants have many strategies to fight off pests. For example, they can produce a slew of different chemical toxins against predators and parasites or they can induce rapid cell death to prevent the spread of infectious agents. Plants can also respond to volatile signals produced by other plants. [36] [37] Jasmonate levels also increase rapidly in response to mechanical perturbations such as tendril coiling. [38]
In plants, the mechanism responsible for adaptation is signal transduction. [39] [40] [41] [42] Adaptive responses include:
Plants do not have brains or neuronal networks like animals do; however, reactions within signalling pathways may provide a biochemical basis for learning and memory in addition to computation and basic problem solving. [50] [51] Controversially, the brain is used as a metaphor by some plant perception researchers to provide an integrated view of signalling. [52]
Plants respond to environmental stimuli by movement and changes in morphology. They communicate while actively competing for resources. In addition, plants accurately compute their circumstances, use sophisticated cost–benefit analysis, and take tightly controlled actions to mitigate and control diverse environmental stressors. Plants are also capable of discriminating between positive and negative experiences and of learning by registering memories from their past experiences. [53] [54] [55] [56] [57] Plants use this information to adapt their behaviour in order to survive present and future challenges of their environments.
Plant physiology studies the role of signalling to integrate data obtained at the genetic, biochemical, cellular, and physiological levels, in order to understand plant development and behaviour. The neurobiological view sees plants as information-processing organisms with rather complex processes of communication occurring throughout the individual plant. It studies how environmental information is gathered, processed, integrated, and shared (sensory plant biology) to enable these adaptive and coordinated responses (plant behaviour); and how sensory perceptions and behavioural events are 'remembered' in order to allow predictions of future activities upon the basis of past experiences. Plants, it is claimed by some[ who? ] plant physiologists, are as sophisticated in behaviour as animals, but this sophistication has been masked by the time scales of plants' responses to stimuli, which are typically many orders of magnitude slower than those of animals.[ citation needed ]
It has been argued that although plants are capable of adaptation, it should not be called intelligence per se, as plant neurobiologists rely primarily on metaphors and analogies to argue that complex responses in plants can only be produced by intelligence. [58] "A bacterium can monitor its environment and instigate developmental processes appropriate to the prevailing circumstances, but is that intelligence? Such simple adaptation behaviour might be bacterial intelligence but is clearly not animal intelligence." [59] However, plant intelligence fits a definition of intelligence proposed by David Stenhouse in a book about evolution and animal intelligence, in which he describes it as "adaptively variable behaviour during the lifetime of the individual". [60] Critics of the concept have also argued that a plant cannot have goals once it is past the developmental stage of seedling because, as a modular organism, each module seeks its own survival goals and the resulting organism-level behavior is not centrally controlled. [59] This view, however, necessarily accommodates the possibility that a tree is a collection of individually intelligent modules cooperating, competing, and influencing each other to determine behavior in a bottom-up fashion. The development into a larger organism whose modules must deal with different environmental conditions and challenges is not universal across plant species, however, as smaller organisms might be subject to the same conditions across their bodies, at least, when the below and aboveground parts are considered separately. Moreover, the claim that central control of development is completely absent from plants is readily falsified by apical dominance. [61]
The Italian botanist Federico Delpino wrote on the idea of plant intelligence in 1867. [62] Charles Darwin studied movement in plants and in 1880 published a book, The Power of Movement in Plants . Darwin concludes:
It is hardly an exaggeration to say that the tip of the radicle thus endowed [..] acts like the brain of one of the lower animals; the brain being situated within the anterior end of the body, receiving impressions from the sense-organs, and directing the several movements.
In 2020, Paco Calvo studied the dynamic of plant movements and investigated whether French beans deliberately aim for supporting structures. [63] Calvo said: “We see these signatures of complex behaviour, the one and only difference being is that it’s not neural-based, as it is in humans. This isn’t just adaptive behaviour, it’s anticipatory, goal-directed, flexible behaviour.” [64]
In philosophy, there are few studies of the implications of plant perception. Michael Marder put forth a phenomenology of plant life based on the physiology of plant perception. [65] Paco Calvo Garzon offers a philosophical take on plant perception based on the cognitive sciences and the computational modeling of consciousness. [66]
Plant sensory and response systems have been compared to the neurobiological processes of animals. Plant neurobiology concerns mostly the sensory adaptive behaviour of plants and plant electrophysiology. Indian scientist J. C. Bose is credited as the first person to research and talk about the neurobiology of plants. Many plant scientists and neuroscientists, however, view the term "plant neurobiology" as a misnomer, because plants do not have neurons. [58]
The ideas behind plant neurobiology were criticised in a 2007 article [58] published in Trends in Plant Science by Amedeo Alpi and 35 other scientists, including such eminent plant biologists as Gerd Jürgens, Ben Scheres, and Chris Sommerville. The breadth of fields of plant science represented by these researchers reflects the fact that the vast majority of the plant science research community rejects plant neurobiology as a legitimate notion.[ citation needed ] Their main arguments are that: [58]
The authors call for an end to "superficial analogies and questionable extrapolations" if the concept of "plant neurobiology" is to benefit the research community. [58] Several responses to this criticism have attempted to clarify that the term "plant neurobiology" is a metaphor and that metaphors have proved useful on previous occasions. [67] [68] Plant ecophysiology describes this phenomenon.
The concepts of plant perception, communication, and intelligence have parallels in other biological organisms for which such phenomena appear foreign to or incompatible with traditional understandings of biology, or have otherwise proven difficult to study or interpret. Similar mechanisms exist in bacterial cells, choanoflagellates, fungal hyphae, and sponges, among many other examples. All of these organisms, despite being devoid of a brain or nervous system, are capable of sensing their immediate and momentary environment and responding accordingly. In the case of unicellular life, the sensory pathways are even more primitive in the sense that they take place on the surface of a single cell, as opposed to within a network of many related cells.
A hormone is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are required for the correct development of animals, plants and fungi. Due to the broad definition of a hormone, numerous kinds of molecules can be classified as hormones. Among the substances that can be considered hormones, are eicosanoids, steroids, amino acid derivatives, protein or peptides, and gases.
Serotonin or 5-hydroxytryptamine (5-HT) is a monoamine neurotransmitter. Its biological function is complex, touching on diverse functions including mood, cognition, reward, learning, memory, and numerous physiological processes such as vomiting and vasoconstriction. This multifacetedness has led to its study being described as "like the fable of the blind men and the elephant".
Shade avoidance is a set of responses that plants display when they are subjected to the shade of another plant. It often includes elongation, altered flowering time, increased apical dominance and altered partitioning of resources. This set of responses is collectively called the shade-avoidance syndrome (SAS).
Systemin is a plant peptide hormone involved in the wound response in the family Solanaceae. It was the first plant hormone that was proven to be a peptide having been isolated from tomato leaves in 1991 by a group led by Clarence A. Ryan. Since then, other peptides with similar functions have been identified in tomato and outside of the Solanaceae. Hydroxyproline-rich glycopeptides were found in tobacco in 2001 and AtPeps were found in Arabidopsis thaliana in 2006. Their precursors are found both in the cytoplasm and cell walls of plant cells, upon insect damage, the precursors are processed to produce one or more mature peptides. The receptor for systemin was first thought to be the same as the brassinolide receptor but this is now uncertain. The signal transduction processes that occur after the peptides bind are similar to the cytokine-mediated inflammatory immune response in animals. Early experiments showed that systemin travelled around the plant after insects had damaged the plant, activating systemic acquired resistance, now it is thought that it increases the production of jasmonic acid causing the same result. The main function of systemins is to coordinate defensive responses against insect herbivores but they also affect plant development. Systemin induces the production of protease inhibitors which protect against insect herbivores, other peptides activate defensins and modify root growth. They have also been shown to affect plants' responses to salt stress and UV radiation. AtPEPs have been shown to affect resistance against oomycetes and may allow A. thaliana to distinguish between different pathogens. In Nicotiana attenuata, some of the peptides have stopped being involved in defensive roles and instead affect flower morphology.
Anthony James Trewavas 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 investigates plant behaviour.
In the study of the biological sciences, biocommunication is any specific type of communication within (intraspecific) or between (interspecific) species of plants, animals, fungi, protozoa and microorganisms. Communication basically means sign-mediated interactions following three levels of rules. Signs in most cases are chemical molecules (semiochemicals), but also tactile, or as in animals also visual and auditive. Biocommunication of animals may include vocalizations, or pheromone production, chemical signals between plants and animals, and chemically mediated communication between plants and within plants.
A pulvinus is a joint-like thickening at the base of a plant leaf or leaflet that facilitates growth-independent movement. Pulvini are common, for example, in members of the bean family Fabaceae (Leguminosae) and the prayer plant family Marantaceae.
Phototaxis is a kind of taxis, or locomotory movement, that occurs when a whole organism moves towards or away from a stimulus of light. This is advantageous for phototrophic organisms as they can orient themselves most efficiently to receive light for photosynthesis. Phototaxis is called positive if the movement is in the direction of increasing light intensity and negative if the direction is opposite.
Catasetum fimbriatum, the fringed catasetum, is a member of the orchid family of flowering plants and lives in a warm tropical environment. This plant uses a fascinating strategy to spread its pollen to other flowers via insects, primarily bees. When a pollinator lands on male flowers of C. fimbriatum and stimulates them, pollen is planted onto the back of the pollinator. This assures their gametes will be spread to other flowers the bee visits of the same species.
Plant rights are rights to which plants may be entitled. Such issues are often raised in connection with discussions about human rights, animal rights, biocentrism, or sentiocentrism.
In molecular biology mir-398 microRNA is a short RNA molecule. MicroRNAs function to regulate the expression levels of other genes by several mechanisms.
Plant cognition or plant gnosophysiology is the study of the learning and memory of plants, exploring the idea it is not only animals that are capable of detecting, responding to and learning from internal and external stimuli 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 systems. The implications are contested; whether plants have cognition or are simply animated objects.
Plant bioacoustics refers to the creation of sound waves by plants. Measured sound emissions by plants as well as differential germination rates, growth rates and behavioral modifications in response to sound are well documented. Plants detect neighbors by means other than well-established communicative signals including volatile chemicals, light detection, direct contact and root signaling. Because sound waves travel efficiently through soil and can be produced with minimal energy expenditure, plants may use sound as a means for interpreting their environment and surroundings. Preliminary evidence supports that plants create sound in root tips when cell walls break. Because plant roots respond only to sound waves at frequencies which match waves emitted by the plants themselves, it is likely that plants can receive and transduce sound vibrations into signals to elicit behavioral modifications as a form of below ground communication.
Plants can be exposed to many stress factors such as disease, temperature changes, herbivory, injury and more. Therefore, in order to respond or be ready for any kind of physiological state, they need to develop some sort of system for their survival in the moment and/or for the future. Plant communication encompasses communication using volatile organic compounds, electrical signaling, and common mycorrhizal networks between plants and a host of other organisms such as soil microbes, other plants, animals, insects, and fungi. Plants communicate through a host of volatile organic compounds (VOCs) that can be separated into four broad categories, each the product of distinct chemical pathways: fatty acid derivatives, phenylpropanoids/benzenoids, amino acid derivatives, and terpenoids. Due to the physical/chemical constraints most VOCs are of low molecular mass, are hydrophobic, and have high vapor pressures. The responses of organisms to plant emitted VOCs varies from attracting the predator of a specific herbivore to reduce mechanical damage inflicted on the plant to the induction of chemical defenses of a neighboring plant before it is being attacked. In addition, the host of VOCs emitted varies from plant to plant, where for example, the Venus Fly Trap can emit VOCs to specifically target and attract starved prey. While these VOCs typically lead to increased resistance to herbivory in neighboring plants, there is no clear benefit to the emitting plant in helping nearby plants. As such, whether neighboring plants have evolved the capability to "eavesdrop" or whether there is an unknown tradeoff occurring is subject to much scientific debate. As related to the aspect of meaning-making, the field is also identified as phytosemiotics.
Integrin-like receptors (ILRs) are found in plants and carry unique functional properties similar to true integrin proteins. True homologs of integrins exist in mammals, invertebrates, and some fungi but not in plant cells. Mammalian integrins are heterodimer transmembrane proteins that play a large role in bidirectional signal transduction. As transmembrane proteins, integrins connect the extracellular matrix (ECM) to the plasma membrane of the animal cell. The extracellular matrix of plant cells, fungi, and some protist is referred to as the cell wall. The plant cell wall is composed of a tough cellulose polysaccharide rather than the collagen fibers of the animal ECM. Even with these differences, research indicates that similar proteins involved in the interaction between the ECM and animals cells are also involved in the interaction of the cell wall and plant cells.
Stefano Mancuso is an Italian botanist, professor of the Agriculture, Food, Environment and Forestry department at his alma mater, the University of Florence. He is the director of the International Laboratory of Plant Neurobiology, steering committee member of the Society of Plant Signaling and Behavior, editor-in-chief of the Plant Signaling & Behavior journal and a member of the Accademia dei Georgofili.
Plant nucleus movement is the movement of the cell nucleus in plants by the cytoskeleton.
In plant biology, plant memory describes the ability of a plant to retain information from experienced stimuli and respond at a later time. For example, some plants have been observed to raise their leaves synchronously with the rising of the sun. Other plants produce new leaves in the spring after overwintering. Many experiments have been conducted into a plant's capacity for memory, including sensory, short-term, and long-term. The most basic learning and memory functions in animals have been observed in some plant species, and it has been proposed that the development of these basic memory mechanisms may have developed in an early organismal ancestor.
“The Nervous Mechanism of Plants”, published in 1926, is a botany book by Sir Jagadish Chandra Bose which summarises his most recent findings in the area of plant physiology. Bose had previously investigated this topic in books such as Plant response as a means of physiological investigation from 1906, or The physiology of photosynthesis, published in 1924. In this book, he proposes that the response mechanisms of plants to stimuli are physiologically similar to those in animals.
Phonotropism is the growth of organisms in response to sound stimuli. Root phonotropism is when the roots of a plant grow towards or away in response to a sound source. Acoustic cues are detected by the plant as sound waves which then induces a mechanistic response that changes plant behavior. Plants adapt to respond to external stimuli because of their sessile nature, and it is evolutionarily plausible that these organisms have adapted to take advantage of these inputs to help foraging behavior or defense mechanisms. Arabidopsis roots have been observed to gravitate towards sounds of flowing water, while caterpillar feeding vibrations alone are sufficient to alter plant defense hormones and volatile emissions in Arabidopsis leaves.
when it is touched, its leaves fold up and its branches droop, leaving it looking dead or sick in a matter of seconds