Articles
RESPONSES OF PLANT MORPHOGENESIS TO MECHANICAL STRESSES: AN INTEGRATED APPROACH
Some illustrations of the work carried out in Clermont-Ferrand according to this scheme will be given.
Research is currently being conducted with tomato plants (Lycopersicon esculentum L.) but results obtained with two other plant species, Bryonia dioica and Bidens pilosa will be also given as a demonstration of the approach.
So far, the experiments have involved pricking or rubbing of some plant organs (cotyledons, internodes, and petioles). Such treatments led to what is called thigmomorphogenetic responses of the plant, that is to say a decrease in internode elongation rate and an increase in radial growth.
Surprisingly, more is known to-day of the cellular events occurring after mechanical perturbations than of the behaviour of the whole plant under mechanical stress.
In particular, only a few reports exist concerning the characterization of the mechanical stimulus perceived at the level of the organ, tissue or cell when a plant is mechanically loaded.
We shall show how the problem can be posed in terms of plant biomechanics when the plant stem is bent: it is then possible to plot the modification of elongation rate as a function of the stress or the strain imposed on the plant.
Concerning the cellular events that occur after mechanical perturbation of the plasmalemma, some results will be given to illustrate the successive stages of the stimulus-response coupling process: the modification of physico-chemical properties of the plasmalemma, the role of calcium and calcium and calcium-binding proteins, membrane depolarization, and the expression of genes coding for enzymes involved in pathways related to cell growth.
In conclusion, we shall demonstrate that the same conceptual framework may be used to analyze the effects of different environmental signals on plant elongation and could allow, for instance, study of the way in which changes in light quality and mechanical stresses interact to control plant morphogenesis.