Plant neurobiology
Encyclopedia
Plant neurobiology studies those aspects of plant physiology
with perceived similarities to the neurobiological processes of animal
s. 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.
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 ecosystem
s 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. 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.
s) 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 organism
s. 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.
s, GABA receptor
s, and endocannabinoid signaling components. They also use ATP
, NO
, and ROS
like animals for signaling.
, 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:
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 physiology
Plant physiology is a subdiscipline of botany concerned with the functioning, or physiology, of plants. Closely related fields include plant morphology , plant ecology , phytochemistry , cell biology, and molecular biology.Fundamental processes such as photosynthesis, respiration, plant nutrition,...
with perceived similarities to the neurobiological processes of animal
Animal
Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...
s. It concerns mostly the sensory adaptive behaviour of plants and plant electrophysiology
Electrophysiology
Electrophysiology is the study of the electrical properties of biological cells and tissues. It involves measurements of voltage change or electric current on a wide variety of scales from single ion channel proteins to whole organs like the heart...
. 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.
Adaptive behaviour
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 stimuliStimulus (physiology)
In physiology, a stimulus is a detectable change in the internal or external environment. The ability of an organism or organ to respond to external stimuli is called sensitivity....
by movement
Tropism
A tropism is a biological phenomenon, indicating growth or turning movement of a biological organism, usually a plant, in response to an environmental stimulus. In tropisms, this response is dependent on the direction of the stimulus...
and changes in morphology
Plant morphology
Plant morphology or phytomorphology is the study of the physical form and external structure of plants. This is usually considered distinct from plant anatomy, which is the study of the internal structure of plants, especially at the microscopic level...
. 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
Cost-benefit analysis
Cost–benefit analysis , sometimes called benefit–cost analysis , is a systematic process for calculating and comparing benefits and costs of a project for two purposes: to determine if it is a sound investment , to see how it compares with alternate projects...
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
Plant hormone
Plant hormones are chemicals that regulate plant growth, which, in the UK, are termed 'plant growth substances'. Plant hormones are signal molecules produced within the plant, and occur in extremely low concentrations. Hormones regulate cellular processes in targeted cells locally and, when moved...
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
Signal transduction
Signal transduction occurs when an extracellular signaling molecule activates a cell surface receptor. In turn, this receptor alters intracellular molecules creating a response...
, communication and behaviour to integrate data obtained at the genetic
Plant genetics
Plant genetics is a very broad term. There are many facets of genetics in general, and of course there are many facets to plants.The definition of genetics is the branch of biology that deals with heredity, especially the mechanisms of hereditary transmission and the variation of inherited...
, molecular, biochemical
Phytochemistry
Phytochemistry is in the strict sense of the word the study of phytochemicals. These are chemicals derived from plants. In a narrower sense the terms are often used to describe the large number of secondary metabolic compounds found in plants. Many of these are known to provide protection against...
and cellular
Cellular
Cellular may refer to:*Cellular automaton, a model in discrete mathematics*Cellular , a 2004 movie*Cellular frequencies, assigned to networks operating in cellular RF bands*Cellular manufacturing...
levels, with the physiology, development and behaviour of individual organisms, plant ecosystem
Phytocoenosis
Plant community is a collection of plant species within a designated geographical unit, which forms a relatively uniform patch, distinguishable from neighbouring patches of different vegetation types. The components of each plant community are influenced by soil type, topography, climate and human...
s and evolution
Plant evolution
Plant evolution is the subset of evolutionary phenomena that concern plants. Evolutionary phenomena are characteristics of populations that are described by averages, medians, distributions, and other statistical methods. This distinguishes plant evolution from plant development, a branch of...
.
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
Order of magnitude
An order of magnitude is the class of scale or magnitude of any amount, where each class contains values of a fixed ratio to the class preceding it. In its most common usage, the amount being scaled is 10 and the scale is the exponent being applied to this amount...
slower than animals'.
Plant neurobiologists rely primarily on metaphors and analogies to argue that complex responses in plants can only be produced by intelligence. 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.
Electrophysiology
Plant cells can be electrically excitable and can display rapid electrical responses (action potentialAction potential
In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...
s) to environmental stimuli. These action potentials can influence processes such as actin
Actin
Actin is a globular, roughly 42-kDa moonlighting protein found in all eukaryotic cells where it may be present at concentrations of over 100 μM. It is also one of the most highly-conserved proteins, differing by no more than 20% in species as diverse as algae and humans...
-based cytoplasmic streaming, plant organ movements, wound responses, respiration, photosynthesis
Photosynthesis
Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
and flowering.
These electrical responses can cause the synthesis of numerous organic molecules
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...
including ones that act as neuroactive substances in other organism
Organism
In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
s. Thus, plants accomplish behavioural responses
Behavior
Behavior or behaviour refers to the actions and mannerisms made by organisms, systems, or artificial entities in conjunction with its environment, which includes the other systems or organisms around as well as the physical environment...
to environmental, communicative, and ecological
Plant ecology
Plant ecology is a subdiscipline of ecology which studies the distribution and abundance of plants, the interactions among and between members of plant species, and their interactions with their environment...
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.
Neurochemicals
Plants produce several proteins found in the animal neuron systems such as acetylcholine esterase, glutamate receptorGlutamate receptor
Glutamate receptors are synaptic receptors located primarily on the membranes of neuronal cells. Glutamate is one of the 20 amino acids used to assemble proteins and as a result is abundant in many areas of the body, but it also functions as a neurotransmitter and is particularly abundant in the...
s, GABA receptor
GABA receptor
The GABA receptors are a class of receptors that respond to the neurotransmitter gamma-aminobutyric acid , the chief inhibitory neurotransmitter in the vertebrate central nervous system...
s, and endocannabinoid signaling components. They also use ATP
Adenosine triphosphate
Adenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...
, NO
Nitric oxide
Nitric oxide, also known as nitrogen monoxide, is a diatomic molecule with chemical formula NO. It is a free radical and is an important intermediate in the chemical industry...
, and ROS
Reactive oxygen species
Reactive oxygen species are chemically reactive molecules containing oxygen. Examples include oxygen ions and peroxides. Reactive oxygen species are highly reactive due to the presence of unpaired valence shell electrons....
like animals for signaling.
Criticisms
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 JürgensGerd Jürgens
Professor Gerd Jürgens is a plant developmental biologist currently holding the posts of Director of the Cell Biology Department at the Max Planck Institute for Developmental Biology and Head of the Center for Plant Molecular Biology at the Eberhard-Karls Universität Tübingen...
, 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 plasmodesmataPlasmodesmataPlasmodesmata are microscopic channels which traverse the cell walls of plant cells and some algal cells, enabling transport and communication between them. Species that have plasmodesmata include members of the Charophyceae, Charales and Coleochaetales , as well as all embryophytes, better known...
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.
See also
- EcophysiologyEcophysiologyEcophysiology or environmental physiology is a biological discipline which studies the adaptation of organism's physiology to environmental conditions...
- Plant evolutionary developmental biologyPlant evolutionary developmental biologyEvolutionary developmental biology refers to the study of developmental programs and patterns from an evolutionary perspective. It seeks to understand the various influences shaping the form and nature of life on the planet. Evo-devo arose as a separate branch of science rather recently. An early...
- Plant intelligencePlant intelligenceIn botany, plant intelligence is the ability of plants to sense the environment and adjust their morphology, physiology and phenotype accordingly...