Membrane function and growth regulation in plants

Change of membrane potential is well known to play a key role in signal transduction and turger movement in excitable plant tissue (Sibaoka 1966). The electrogenic nature of some ion pump in fungal and plant cells has already been demonstrated (Slayman 1965, Higinbotham et al. 1970). This electrogenic ion pump was found to be a proton extruding one fueled by ATP (Kitasato 1968, Shimmen and Tazawa 1977). At the same time, the acid growth hypothesis for the action of auxininduced promotion of plant elongation growth appeared (Hager et al. 1971, Rayle and Cleland 1970). A close correlation between electrogenic proton transport and elongation growth was indicated in the stem (Katou and Okamoto 1970). Furthermore, fusicoccin-induced promotion of growth with electrogenic H+ extrusion (Marre 1979) and IAA-induced hyperpolarization of the plasma membrane have been demonstrated (Cleland et at. 1977). Through these studies, it has been gradually recognized that proton transport plays an important role in plant growth. Much progress has been made in the biophysical, biochemical and cell physiological studies of membrane transport. It has been revealed that proton pump and ion channels play crucial roles in signal transduction, turgor regulation, cell motility, etc. As a consequence, it has become possible to discuss various aspects of the function of membranes in the integrated activities of plants such as growth and stress adaptation (Dainty et al. 1989). During the last fifteen years or so, we have held a series of symposia and workshops on membrane function in plants (Tazawa et al. 1989). The last symposium was held at Nagoya in November 1994 on the occasion of the retirement of Professor Hisashi Okamoto from Yokohama City University. Professor Okamoto did the major portion of his work at Nagoya University.