Long-distance transport, storage and recall of morphogenetic information in plants. The existence of a sort of primitive plant 'memory'.

An asymmetrical treatment of Bidens seedlings (pricking one of the seedling cotyledons) causes the cotyledonary buds to grow asymmetrically after release of apical dominance by decapitation of the seedlings. The symmetry-breaking signal propagates within the seedlings at a rate of at least a fraction of a millimetre per second. This information may be 'stored' (STO function) within the seedlings, without taking effect, for at least 2 weeks; then the information may be 'recalled' (RCL function), thus permitting transduction of the signal into the final response (differential growth of the buds), as a consequence of subjecting the seedlings to various symmetrical or asymmetrical treatments. A similar behaviour was observed with stimuli other than pricking (including non-traumatic stimuli), with plants other than Bidens (flax, tomato), and with responses other than cotyledonary-bud growth (hypocotyl elongation, induction of meristems, thigmomorphogenesis). There are indications that storage may involve the activation of elements implicated in cell cycle control, and that the last steps of the final response involve genes such as tch1 and hsp70. The adaptive advantage for plants in possessing STO/RCL functions is discussed. Manipulating the STO/RCL functions may have interesting practical applications, e.g. in the resistance of plants to natural stresses. The existence of the STO/RCL functions in plants constitutes an elementary form of 'memory' which may provide an experimental system simpler than the animal brain to test the validity of the theoretical models of interpretation of important features such as memory storage and evocation.