Plant neurobiology studies those aspects of plant physiology with perceived similarities to the neurobiological processes of animals. It concerns mostly the sensory adaptive behaviour of plants and plant electrophysiology. J. C. Bose the Indian scientist is credited as the first person to research and talk about neurobiology of plants. Many plant scientists however view it as controversial.[1]
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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.
Furthermore they systematically use hormonal signalling pathways to coordinate their own development and morphology.
Plant neurobiology is a discipline of plant science which is on the fringes of accepted science. The discipline claims to study 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. Plant neurobiology researches how environmental information is gathered, processed, integrated and shared (sensory plant biology) to enable this 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 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'.
Plant neurobiologists rely primarily on metaphors and analogies to argue that complex responses in plants can only be produced by intelligence.[1] Since animal intelligence is achieved with brains and neurons, the argument is made that plants must also have brains and neurons; this argument is rejected by the majority of plant scientists. Other arguments include the fact that the word neuron originally meant plant fiber in Greek, that a chemical produced by a plant is structurally similar to a chemical involved in animal neurobiology, or that plant cells might use electrical signals. While these are interesting facts, they are not really evidence of neurons, brains, intelligence or neurobiology.
Plant cells 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.[2][3][4]
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 to environmental, communicative, and ecological contexts.
This electrophysiology of plants probably reflects the basic limitation that all life must work within the physical laws of matter and that electrical signals are one of the only ways any organism can send a fast signal between cells. While many cells in nearly all living organisms can be electrically excitable, this is not evidence of neurons, or of intelligence.
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.[5]
The ideas behind plant neurobiology were criticised in a 2007 article[6] 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[1]:
The authors call for an end to "superficial analogies and questionable extrapolations" if the concept of "plant neurobiology" is to benefit the research community.[7]
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.[8][9]