In contrast to animals, plants are immobile and, thus, cannot leave a drastically changed environment. Therefore, plants have developped specific strategies involving particular signal and transduction systems as well as a form of cellular organization that allow them to buffer against sudden changes in external conditions. This state-of-the-art summary written by leading scientists deals with: - the most recent data available on the molecular mechanism involved in the response of plant cells to different stimuli; - the critical domaine of ignorance such as the signifi cance of site occupancy of receptors for growth substances; - the estimation of the applicability of new techniques such as electrophysiology, cell imaging and DNA recombinant technology; - directions for future work.