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

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.