Plant neurobiology and green plant intelligence: science, metaphors and nonsense

Abstract

This paper analyses the recent debates on the emerging science of plant neurobiology, which claims that the individual green plant should be considered as an intelligent organism. Plant neurobiology tries to use elements from animal physiology as elegant metaphors to trigger the imagination in solving complex plant physiological elements of signalling, internal and external plant communication and whole-plant organisation. Plant neurobiology proposes useful concepts that stimulate discussions on plant behaviour. To be considered a new science, its added value to existing plant biology needs to be presented and critically evaluated. A general, scientific approach is to follow the so-called 'parsimony principle', which calls for simplest ideas and the least number of assumptions for plausible explanation of scientific phenomena. The extent to which plant neurobiology agrees with or violates this general principle needs to be examined. Nevertheless, innovative ideas on the complex mechanisms of signalling, communication, patterning and organisation in higher plants are badly needed. We present current views on these mechanisms and the specific role of auxins in regulating them.  2007 Society of Chemical IndustryKeywords: communication; organisation; patterning; plant neurobiology; plant intelligence; signalling INTRODUCTIONEnormous progress in knowledge on the molecular biology and genetics of plants has highlighted the complexity of plant metabolism and its regulation under variable and often stressful environmental conditions. Plant scientists wonder how the plant, as an autonomous organism, is capable of managing its internal complexity and the myriad of information it is exposed to in order to maximise its fitness, i.e. its capability to survive under stress and propagate its genes. There is a need for new concepts on how plants perceive signals, how plants arrange internal communication within the (nuclear or other) genome, within cells, between cells and between tissues or organs, and how the plasticity of the whole plant is organised. Plant neurobiology offers such a concept, borrowing metaphors, images and ideas from animal physiology. Plant neurobiology assumes the existence in green plants of structures equivalent to those known from animal physiology, such as synapses * , neurons, rapid signalling and communication systems, including an organisation

Root decisions

“…However, while this new field does have some support (see Trewavas 2007), others have argued it adds very little to what could already be described under the existing areas of plant cell biology, physiology or signalling (Alpi et al. 2007; Struik, Yin & Meinke 2008). The purpose of this review was not to be drawn into this debate of plant ‘neurobiology’ but, rather, to review the literature on how roots respond both to some key environmental problems they face as part of their normal growth and function, and how they respond to other plant roots.…”

Molecular mechanisms underlying plant memory in JA‐mediated defence responses

“…Plants show hallmarks of anoetic consciousness: they perceive environmental signals and store information carried by these signals in various forms, including changes in concentration of small molecules, abundance of proteins or modifications of their genetic material (e.g. methylation), or structural scaffold supporting DNA molecules in the cells (histone acetylation and deacetylation) (Trewavas 2003, 2005; Struik, Yin & Meinke 2008). Plants can respond at the level of a single cell to the entire multicellular organism: individual cells are able to store information about the orientation of newly formed cell walls during cytokinesis (Lloyd & Buschmann 2007), and whole plants can store permanent memories of cold exposure known as vernalization (Michaels & Amasino 2000).…”

Plants and Animals: Convergent Evolution in Action?

“…Besides plant neurobiology and intelligence, there are other examples of convergent evolution between plants and animals (Table 1 ). Thus, plant intelligence (Trewavas 2003(Trewavas , 2005a(Trewavas , b, 2007 and cognition (Calvo Garzon 2007) , as well as the whole emerging field of plant neurobiology, may prove to be important phenomena as we attempt to improve our understanding of the elusive processes that "channel" biological evolution towards similar states despite different outcome situations (Conway Morris 2003 , Recently, Struik et al (2008) questioned the validity of the concept of plant neurobiology by arguing against the parsimony principle, also known as "Occam's razor," which suggests that the most plausible concept is the one that is based on the simplest ideas and requires the fewest assumptions. However, Francis Crick has commented on the potential limitations of Occam's razor in biology (Crick 1988) .…”