Plant perception (physiology)
In botany, plant perception is the ability of plants to sense the environment and adjust their morphology, physiology and phenotype accordingly. Research draws on the fields of plant physiology, ecology and molecular biology. Examples of stimuli which plants perceive and can react to include chemicals, gravity, light, moisture, infections, temperature, oxygen and carbon dioxide concentrations, parasite infestation, physical disruption, sound, and touch. Plants have a variety of means to detect such stimuli and a variety of reaction responses or behaviors.
Plant perception occurs on a cellular level. Research published in September 2006 has shown, certainly in the case of Arabidopsis thaliana, the role of cryptochromes in the perception of magnetic fields by plants. Mechanical perturbation can also be detected by plants. Poplar stems can detect reorientation and inclination (equilibrioception).
Plant response strategies depend on quick and reliable recognition-systems.
Wounded tomatoes are known to produce the volatile odour methyl-jasmonate as an alarm-signal. Plants in the neighbourhood 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's 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 the day with a molecular clock. This internal clock is set to the solar clock every day using sunlight. 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 whereas when the light is very bright and/or if the levels of harmful UV increase, plants produce more of their protective pigments that act as sunscreens.
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 are not passive entities merely subject to environmental forces, nor are they 'automata'-like organisms based only on reflexes and optimised solely for accumulation of photosynthate. Plants respond sensitively to environmental stimuli by movement and changes in morphology. They signal and communicate within and among themselves as they actively compete for limited resources, both above and below ground. 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. Plants are also capable of refined recognition of self and non-self, and are territorial in behaviour.
Plant physiology studies the role of signalling, communication and behaviour to integrate data obtained at the genetic, molecular, biochemical and cellular levels, with the physiology, development and behaviour of individual organisms, plant ecosystems and evolution. 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 plantlet because, as a modular organism, each module seeks its own survival goals and the resultant whole organism behavior is not centrally controlled. This view, however, necessarily accomodates the possibilty that a tree is a collection of individually intelligent modules cooperating, competing and influencing each other, thus determining organism level behavior from the base up. The development into a larger organism whose modules must deal with different environmental conditions and challenges is not universal across plant species either, as smaller organisms might be subject to the same conditions across their bodies, at least, when the below and above ground parts are consdiered 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. The 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.
- Auxin - A plant hormone which mediates responses
- Chemotropism - Plant response to chemicals
- Cryptochrome - A light receptor pigment
- Ethylene - A plant hormone which mediates responses
- Gravitropism - Behavior associated with gravitic perception
- Heliotropism - Behavior associated with sunlight perception
- Hormonal sentience - Plant information processing theory
- 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
- Phototropin - A light receptor pigment
- Phototropism - A behavior associated with light perception
- Phytochrome - A light receptor pigment
- 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 hormone - A mediator of response to stimuli
- Plant perception (paranormal)
- Plant physiology - The science of plant function
- 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
- Thigmotropism - Plant response to touch
- 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.
- 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. doi:10.1093/beheco/ars228.
- The "sixth sense" of plants
- 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 2649404. PMID 19129416.
- Pickard, B. G. (1973). "Action Potentials in Higher Plants". Botanical Review 39 (2): 172–201. doi:10.1007/BF02859299. JSTOR 4353850.
- Proc Natl Acad Sci U S A. 1990 October; 87(19): 7713–7716. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC54818/
- 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. doi:10.1023/A:1007893626166.
- Falkenstein, E.; Groth, B.; Mith�fer, A.; Weiler, E. (1991). "Methyljasmonate and ?-linolenic acid are potent inducers of tendril coiling". Planta 185 (3). doi:10.1007/BF00201050.
- 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 33554. 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. doi:10.1023/A:1019640813676.
- Hutchings, M.; Dekroon, H. (1994). "Foraging in Plants: the Role of Morphological Plasticity in Resource Acquisition" 25. p. 159. 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?" 28. p. 145. doi:10.1016/S0065-2504(08)60032-X.
- Åke Strid and Robert J. Porra. Alterations in Pigment Content in Leaves of Pisum sativum After Exposure to Supplementary UV-B. Plant and Cell Physiology, 1992, Vol. 33, No. 7 1015-1023
- 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.
- Plant neurobiology: no brain, no gain? Alpi A, Amrhein N, Bertl A, Blatt MR, Blumwald E, Cervone F, Dainty J, De Michelis MI, Epstein E, Galston AW, Goldsmith MH, Hawes C, Hell R, Hetherington A, Hofte H, Juergens G, Leaver CJ, Moroni A, Murphy A, Oparka K, Perata P, Quader H, Rausch T, Ritzenthaler C, Rivetta A, Robinson DG, Sanders D, Scheres B, Schumacher K, Sentenac H, Slayman CL, Soave C, Somerville C, Taiz L, Thiel G, Wagner R. (2007). Trends Plant Sci. Apr;12(4):135-6. 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.
- 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
- Gilroy S, Masson PH (2007) Plant Tropisms. Iowa State University Press
- Karban R (2008) Plant behaviour and communication. Ecol Lett 11: 727-739
- Mancuso S, Shabala S (2006) Rhythms in Plants. Springer Verlag
- Scott P (2008) Physiology and Behaviour of Plants. John Willey & Sons Ltd
- Trewavas A (2005) Plant intelligence. Naturwissenschaften 92: 401-413
- Trewavas A (2009) What is plant behaviour? Plant Cell Environm 32: 606-616
- Volkov AG (2006) Plant Electrophysiology. Springer Verlag
- 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, and 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?