Plant perception (physiology)
Plant perception is the ability of plants to sense and respond to the environment to adjust their morphology, physiology, and phenotype accordingly. Other disciplines such as plant physiology, ecology and molecular biology are used to assess this ability. Plants react to chemicals, gravity, light, moisture, infections, temperature, oxygen and carbon dioxide concentrations, parasite infestation, disease, physical disruption, sound, and touch.
Wounded tomatoes are known to produce the volatile odour methyl jasmonate as an alarm signal. Neighbouring plants can then detect the chemical and prepare for the attack by producing chemicals that defend against insects or attract predators.
Plants produce several proteins found in the animal neuron systems such as acetylcholine esterase, glutamate receptors, GABA receptors, and endocannabinoid signaling components. They also use ATP, NO, and ROS like animals for signaling.
Although plant cells are not neurons, they can be electrically excitable and can display rapid electrical responses (action potentials) to environmental stimuli. These action potentials can influence processes such as actin-based cytoplasmic streaming, plant organ movements, wound responses, respiration, photosynthesis, and flowering. These electrical responses can cause the synthesis of numerous organic molecules, including ones that act as neuroactive substances in other organisms. Thus, plants accomplish behavioural responses in environmental, communicative, and ecological contexts.
A plant's concomitant reactive behavior is mediated by phytochromes, kinins, hormones, antibiotic or other chemical release, changes of water and chemical transport, and other means. These responses are generally slow, taking at minimum a number of hours to accomplish, and can best be observed with time-lapse cinematography, but rapid movements can occur as well. Plants respond to volatile signals produced by other plants. Jasmonate levels also increase rapidly in response to mechanical perturbations such as tendril coiling.
Plants have many strategies to fight off pests. For example, they can produce different toxins (phytoalexins) against invaders or they can induce rapid cell death in invading cells to hinder the pests from spreading out.
Some plants are capable of rapid movement: the mimosa plant (Mimosa pudica) makes its thin leaves point down at the slightest touch and carnivorous plants such as the Venus flytrap snap shut by the touch of insects.
Adaptive responses include:
- Active foraging for light and nutrients. They do this by changing their architecture[vague], physiology and phenotype.
- Leaves and branches are positioned and oriented in response to light source.
- Ability to detect soil volume and adapt growth accordingly independently of nutrient availability.
- Adaptively defend against herbivores.
Aspects of perception
Many plant organs contain photo-sensitive compounds (phototropins, cryptochromes and phytochromes), each reacting very specifically to certain wavelengths of light. These light sensors tell the plant if it is day or night, how long the day is, how much light is available and from where the light comes. Shoots grow towards light and roots usually grow away from light. These responses are called phototropism and skototropism respectively. They are brought about by light sensitive pigments like phototropins and phytochromes and the plant hormone auxin. Many plants exhibit certain phenomena at specific times of the day; for example, certain flowers open only in the mornings. Plants keep track of the time of day with a circadian clock. This internal clock is set to solar time every day using sunlight, temperature and other cues, similar to the biological clocks of other organisms. The internal clock coupled with the ability to perceive light also allows plants to measure the time of the day and so find the season of the year. This is how many plants know when to flower. (see photoperiodism) 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 UV increase, plants produce more of their protective pigments that act as sunscreens.
To orient themselves correctly, plants must have an adequate sense of the direction of gravity’s unidirectional pull. The subsequent response plant movement is known as gravitropism. Typically, in the root this works as gravity is sensed and translated in the root tip, and subsequently roots grow towards gravity via elongation of the cells. In the shoot, similar effects are happening, but gravity is perceived and then growth occurs in the opposite direction, as the above ground part of the plant experiences negative gravitropism.
At the root tip, there are amyloplasts containing starch granules that fall in the direction of gravity. This weight activates secondary receptors, which signal to the plant the direction of 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 happen, the plant must 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.
Plants do not have a brain or neuronal network, but reactions within signalling pathways may provide a biochemical basis for learning and memory in addition to computation and problem solving. Controversially, the brain is used as a metaphor in plant intelligence to provide an integrated view of signalling.
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 positive and negative experiences and of "learning" (registering memories) from their past experiences. Plants use this information to update their behaviour in order to survive present and future challenges of their environment.
Plant physiology studies the role of signalling to integrate data obtained at the genetic, biochemical, cellular and physiological levels 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 organism. 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 plant physiologists, are as sophisticated in behaviour as animals but this sophistication has been masked by the time scales of plants' response to stimuli, many orders of magnitude slower than animals'.
It has been argued that although plants are capable of adaptation, it should not be called intelligence, as plant neurobiologists are relying primarily on metaphors and analogies to argue that complex responses in plants can only be produced by intelligence. "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." However, plant intelligence fits a definition of intelligence proposed by David Stenhouse in a book about evolution and animal intelligence where he described it as "adaptively variable behaviour during the lifetime of the individual". Critics of the concept have also argued that a plant cannot have goals once it is past the development 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. 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 above ground parts are considered separately. Moreover, the claim that central control of development is completely absent from plants is readily falsified by apical dominance.
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 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. Paco Calvo Garzon offers a philosophical take on plant perception based on the cognitive sciences and the computational modeling of consciousness.
Comparison to neurobiology
A plant's sensory and response system has been compared to the neurobiological processes of animals. Plant neurobiology, an unfamiliar misnomer, 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 neurobiology of plants. Many plant scientists and neuroscientists, however, view this as inaccurate, because plants do not have neurons.
The ideas behind plant neurobiology were criticised in a 2007 article 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 reject plant neurobiology. Their main arguments are that:
- "Plant neurobiology does not add to our understanding of plant physiology, plant cell biology or signaling".
- "There is no evidence for structures such as neurons, synapses or a brain in plants".
- The common occurrence of plasmodesmata in plants which "poses a problem for signaling from an electrophysiological point of view" since extensive electrical coupling would preclude the need for any cell-to-cell transport of a ‘neurotransmitter-like’ compounds.
The authors call for an end to "superficial analogies and questionable extrapolations" if the concept of "plant neurobiology" is to benefit the research community.
There were several responses to the criticism clarifying that the term "plant neurobiology" is a metaphor and metaphors have proved useful on several previous occasions. Plant ecophysiology describes this phenomenon.
Parallels in other taxa
As described above in the case of a plant, similar mechanisms exist in a bacterial cell, a choanoflagellate, a fungal hypha, or a sponge, among the many other examples. All of these individual organisms of the respective taxa, 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 single-celled 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 a network of many cells.
- Auxin - A plant hormone which mediates responses
- Biosemiotics - Biological study of meaning making processes
- Chemotropism - Plant response to chemicals
- Ethylene - A plant hormone which mediates responses
- Gravitropism - Behavior associated with gravitic perception
- Heliotropism - Behavior associated with sunlight perception
- Hydrotropism - Plant response to moisture
- Hypersensitive response - Local reaction produced in response to infection by microbes
- Kinesis (biology) - Movement
- Nastic movements - A type of rapid response to non-directional stimulus
- Osmosis - A means of water transportation on the cellular level
- Phytosemiotics - Analysis of vegetative processes on the basis of semiotic theory
- Plant defense against herbivory - Some plant responses to physical disruption
- Plant evolutionary developmental biology
- Plant perception (paranormal)
- Plant tolerance to herbivory
- Rapid plant movement - Description of rapid plant movements
- The Secret Life of Plants
- Sensory receptors - Discussion of organs of perception in organisms
- Statocyte - Cells involved in gravity perception
- Stoma - A plant pore which responds to stimulus and which regulates gas exchange
- Systemic acquired resistance - A "whole-plant" resistance response to microbial pathogens that occurs following an earlier, localized response
- Taxis - A type of response to a directional stimulus seen in motile developmental stages of lower plants
- Thermotropism - Plant response to heat
- Tropism - A type of response to a directional stimulus
- Trewavas, A. (2005). "Green plants as intelligent organisms". Trends in Plant Science. 10 (9): 413–419. doi:10.1016/j.tplants.2005.07.005. PMID 16054860.
- Mishra, Ratnesh Chandra; Ghosh, Ritesh; Bae, Hanhong (2016-08-01). "Plant acoustics: in the search of a sound mechanism for sound signaling in plants". Journal of Experimental Botany. 67 (15): 4483–4494. doi:10.1093/jxb/erw235. ISSN 0022-0957.
- Bailey, N. W.; Fowler-Finn, K. D.; Rebar, D.; Rodriguez, R. L. (2013). "Green symphonies or wind in the willows? Testing acoustic communication in plants". Behavioral Ecology. 24 (4): 797–798. doi:10.1093/beheco/ars228.
- Jaffe, M. J.; Forbes, S. (1993). "Thigmomorphogenesis: the effect of mechanical perturbation on plants". Plant Growth Regulation. 12 (3): 313–24. doi:10.1007/BF00027213. PMID 11541741.
- Azri, W.; Chambon, C.; Herbette, S. P.; Brunel, N.; Coutand, C.; Leplé, J. C.; Ben Rejeb, I.; Ammar, .; Julien, J. L.; Roeckel-Drevet, P. (2009). "Proteome analysis of apical and basal regions of poplar stems under gravitropic stimulation". Physiologia Plantarum. 136 (2): 193–208. doi:10.1111/j.1399-3054.2009.01230.x. PMID 19453506.
- Baluška F, Volkmann D, Mancuso S (2006) Communication in Plants: Neuronal Aspects of Plant Life. Springer Verlag. ISBN 978-3-540-28475-8
- Wagner E, Lehner L, Normann J, Veit J, Albrechtova J (2006). Hydroelectrochemical integration of the higher plant—basis for electrogenic flower induction. pp 369–389 In: Balusˇka F, Mancuso S, Volkmann D (eds) Communication in plants: neuronal aspects of plant life. Springer, Berlin.
- Fromm, J; Lautner, S (2007). "Electrical signals and their physiological significance in plants". Plant Cell Environ. 30 (3): 249–57. doi:10.1111/j.1365-3040.2006.01614.x. PMID 17263772.
- Zimmermann, M. R.; Maischak, H.; Mithofer, A.; Boland, W.; Felle, H. H. (2009). "System Potentials, a Novel Electrical Long-Distance Apoplastic Signal in Plants, Induced by Wounding". Plant Physiology. 149 (3): 1593–1600. doi:10.1104/pp.108.133884. PMC . PMID 19129416.
- Pickard, B. G. (1973). "Action Potentials in Higher Plants". Botanical Review. 39 (2): 172–201. doi:10.1007/BF02859299. JSTOR 4353850.
- Farmer, EE; Ryan, CA (October 1990). "Interplant communication: airborne methyl jasmonate induces synthesis of proteinase inhibitors in plant leaves". Proc. Natl. Acad. Sci. U.S.A. 87: 7713–6. doi:10.1073/pnas.87.19.7713. PMC . PMID 11607107.
- Karban, R.; Baxter, K. J. (2001). "Induced Resistance in Wild Tobacco with Clipped Sagebrush Neighbors: The Role of Herbivore Behavior". Journal of Insect Behavior. 14 (2): 147–156. doi:10.1023/A:1007893626166.
- Falkenstein, E.; Groth, B.; Mithöfer, A.; Weiler, E. (1991). "Methyljasmonate and α-linolenic acid are potent inducers of tendril coiling". Planta. 185 (3). doi:10.1007/BF00201050. PMID 24186412.
- Scheel, Dierk; Wasternack, C. (2002). Plant signal transduction. Oxford: Oxford University Press. ISBN 0-19-963879-9.
- Xiong, L.; Zhu, J. K. (2001). "Abiotic stress signal transduction in plants: Molecular and genetic perspectives". Physiologia Plantarum. 112 (2): 152–166. doi:10.1034/j.1399-3054.2001.1120202.x. PMID 11454221.
- Clark, GB; Thompson Jr, G; Roux, SJ (2001). "Signal transduction mechanisms in plants: an overview". Current Science. 80 (2): 170–7. PMID 12194182.
- Trewavas, A (1999). "How plants learn". Proceedings of the National Academy of Sciences of the United States of America. 96 (8): 4216–8. Bibcode:1999PNAS...96.4216T. doi:10.1073/pnas.96.8.4216. PMC . PMID 10200239.
- De Kroon, H. and Hutchings, M.J. (1995) Morphological plasticity in clonal plants: the foraging concept reconsidered. J. Ecol. 83, 143–152
- Grime, J. P.; MacKey, J. M. L. (2002). "The role of plasticity in resource capture by plants". Evolutionary Ecology. 16 (3): 299–307. doi:10.1023/A:1019640813676.
- Hutchings, M.; Dekroon, H. (1994). "Foraging in Plants: the Role of Morphological Plasticity in Resource Acquisition". Advances in Ecological Research. 25: 159–238. doi:10.1016/S0065-2504(08)60215-9.
- Honda, H.; Fisher, J. (1978). "Tree branch angle: maximizing effective leaf area". Science. 199 (4331): 888–890. Bibcode:1978Sci...199..888H. doi:10.1126/science.199.4331.888. PMID 17757590.
- McConnaughay, K. D. M.; Bazzaz, F. A. (1991). "Is Physical Space a Soil Resource?". Ecology. 72 (1): 94–103. doi:10.2307/1938905. JSTOR 1938905.
- McConnaughay, K. D. M.; Bazzaz, F. A. (1992). "The Occupation and Fragmentation of Space: Consequences of Neighbouring Shoots". Functional Ecology. 6 (6): 711–718. doi:10.2307/2389968. JSTOR 2389968.
- Schenk, H.; Callaway, R.; Mahall, B. (1999). "Spatial Root Segregation: Are Plants Territorial?". Advances in Ecological Research. 28: 145–180. doi:10.1016/S0065-2504(08)60032-X.
- Strid, Åke; Porra, Robert J. (1992). "Alterations in Pigment Content in Leaves of Pisum sativum After Exposure to Supplementary UV-B". Plant and Cell Physiology. 33 (7): 1015–1023.
- Freeman, Scott (2014). Biological science. Illinois: Pearson. p. 803. ISBN 9780321743671. OCLC 821271420.
- Perrin, Robyn M.; Young, Li-Sen; Murthy U M, Narayana; Harrison, Benjamin R.; Wang, Yan; Will, Jessica L.; Masson, Patrick H. (2005-10-01). "Gravity signal transduction in primary roots". Annals of Botany. 96 (5): 737–743. doi:10.1093/aob/mci227. ISSN 0305-7364. PMC . PMID 16033778.
- Bhalla, US; Iyengar, R (1999). "Emergent properties of networks of biological signaling pathways". Science. 283 (5400): 381–7. Bibcode:1999Sci...283..381B. doi:10.1126/science.283.5400.381. PMID 9888852.
- Brenner, E.; Stahlberg, R.; Mancuso, S.; Vivanco, J.; Baluska, F.; Vanvolkenburgh, E. (2006). "Plant neurobiology: an integrated view of plant signaling". Trends in Plant Science. 11 (8): 413–9. doi:10.1016/j.tplants.2006.06.009. PMID 16843034.
- Goh, C. H.; Nam, H. G.; Park, Y. S. (2003). "Stress memory in plants: A negative regulation of stomatal response and transient induction of rd22 gene to light in abscisic acid-entrained Arabidopsis plants". The Plant Journal. 36 (2): 240–255. doi:10.1046/j.1365-313X.2003.01872.x. PMID 14535888.
- Volkov, A. G.; Carrell, H.; Baldwin, A.; Markin, V. S. (2009). "Electrical memory in Venus flytrap". Bioelectrochemistry. 75 (2): 142–147. doi:10.1016/j.bioelechem.2009.03.005. PMID 19356999.
- Rensing, L.; Koch, M.; Becker, A. (2009). "A comparative approach to the principal mechanisms of different memory systems". Naturwissenschaften. 96 (12): 1373–1384. Bibcode:2009NW.....96.1373R. doi:10.1007/s00114-009-0591-0. PMID 19680619.
- Alpi, A; Amrhein, N; Bertl, A; et al. (April 2007). "Plant neurobiology: no brain, no gain?". Trends in Plant Science. 12: 135–6. doi:10.1016/j.tplants.2007.03.002. PMID 17368081.
- Firn, R. (2004). "Plant intelligence: an alternative point of view". Annals of Botany. 93 (4): 345–351. doi:10.1093/aob/mch058. PMID 15023701.
- Marder, M (2012). "Plant intentionality and the phenomenological framework of plant intelligence". Plant Signal Behav. 7: 1365–72. doi:10.4161/psb.21954. PMC . PMID 22951403.
- Garzón, FC (2007). "The quest for cognition in plant neurobiology". Plant Signal Behav. 2: 208–11. doi:10.4161/psb.2.4.4470. PMC . PMID 19516990.
- Trewavas, A. (2007). "Response to Alpi et al.: Plant neurobiology--all metaphors have value". Trends in Plant Science. 12 (6): 231–233. doi:10.1016/j.tplants.2007.04.006. PMID 17499006.
- Brenner, E.; Stahlberg, R.; Mancuso, S.; Baluska, F.; Van Volkenburgh, E. (2007). "Response to Alpi et al.: plant neurobiology: the gain is more than the name". Trends in Plant Science. 12 (7): 285–286. doi:10.1016/j.tplants.2007.06.005. PMID 17591455.
- Baluška F, Mancuso S (ed) (2009). Signalling in Plants. Springer Verlag.
- Baluška F (ed) (2009). Plant-Environment Interactions: From Sensory Plant Biology to Active Plant Behavior. Springer Verlag.
- Brenner, E; Stahlberg, R; Mancuso, S; Vivanco, J; Baluška, F; Van Volkenburgh, E (2006). "Plant Neurobiology: An Integrated View of Plant Signaling". Trends Plant Sci. 11: 413–419. doi:10.1016/j.tplants.2006.06.009. PMID 16843034.
- Cvrckova, F; et al. (2009). "Plant Intelligence: Why, Why Not, or Where?". Plant Signal Behav. 4: 394–399. doi:10.4161/psb.4.5.8276. PMC . PMID 19816094.
- Garzón, FC (2007). "The Quest for Cognition in Plant Neurobiology". Plant Signal Behav. 2: 208–211. doi:10.4161/psb.2.4.4470. PMC . PMID 19516990.
- Gilroy S, Masson PH (2007). Plant Tropisms. Iowa State University Press.
- Karban, R (2008). "Plant Behaviour and Communication". Ecol Lett. 11: 727–739. doi:10.1111/j.1461-0248.2008.01183.x. PMID 18400016.
- Karban R (2015). Plant Sensing and Communication. University of Chicago Press.
- Mancuso S, Shabala S (2006). Rhythms in Plants. Springer Verlag.
- Scott P (2008). Physiology and Behaviour of Plants. John Willey & Sons Ltd.
- Trewavas, A (2003). "Aspects of Plant Intelligence". Ann Bot. 92: 1–20. doi:10.1093/aob/mcg101. PMC . PMID 12740212.
- Trewavas, A (2005). "Plant Intelligence". Naturwissenschaften. 92: 401–413. doi:10.1007/s00114-005-0014-9.
- Trewavas, A (2009). "What is Plant Behaviour?". Plant Cell Environm. 32: 606–616. doi:10.1111/j.1365-3040.2009.01929.x.
- Volkov AG (2006). Plant Electrophysiology. Springer Verlag.
- Volkov, AG (2008). "Plant Electrical Memory". Plant Signal Behav. 3: 490–492. doi:10.4161/psb.3.7.5684. PMC . PMID 19704496.
- Miller, Deborah; Whitney Hable; Jennifer Gottwald; Mary Ellard-Ivey; Taku Demura; Terri Lomax; Nick Carpita (1997). Connections: The Hard Wiring of the Plant Cell for Perception, Signaling, and Response. The Plant Cell 9(12). pp. 2105–2117. Retrieved 2006-12-25.
- Keen, Noel T; Shigeyuki Mayama; Jan E. Leach; Shinji Tsujumu, eds. (2001). Delivery and Perception of Pathogen Signals in Plants. APS Press. p. 268. ISBN 0-89054-259-7.
- Taiz, Lincoln; Eduardo Zeiger (2006). Plant Physiology, fourth edition. Sinauer Associates. p. 700 (est). ISBN 0-87893-856-7.
- Taiz, Lincoln; Eduardo Zeiger (2002). "Plant Physiology Online". a companion to Plant Physiology, Third Edition. Sinauer Associates. Archived from the original on 7 December 2006. Retrieved 2006-12-26.
- Dierk Scheel and Claus Wastermack (May 2002). Plant Signal Transduction. Oxford University Press. p. 346. ISBN 978-0-19-963879-6. Retrieved 2006-12-25.
- Plant Neurobiology Society
- Plant Signaling and Behavior Scientific journal for Plant Neurobiology
- Study hints plants have sensibilities
- Plants cannot "think and remember," but there's nothing stupid about them: They're shockingly sophisticated
- How Does a Venus Flytrap Work?
- Plant Neurobiology: “Foolish distraction” or “new science”?