Involvement of 14-3-3 proteins in the osmotic regulation of H+-ATPase in plant plasma membranes

Taking the binding of fusicoccin to plasma membranes as an indicator of com plex formation between the 14-3-3 dimer and H+-ATPase, we assessed the effe ct of osmotic stress on the interaction of these proteins in suspension-cul tured cells of sugar belt (Beta vulgaris L.). An increase in osmolarity of the cell incubation medium, accompanied by a decrease in turgor. was found to activate the H+ efflux 5-fold. The same increment was observed in the nu mber of high-affinity fusicoccin-binding sites in isolated plasma membranes : the 14-3-3 content in the membranes increased 2- to 3-fold, while the H+- ATPase activity changed only slightly. The data obtained indicate that osmo tic regulation of H+-ATPase in the plant plasma membrane is achieved via mo dulation of the coupling between H+ transport and ATP hydrolysis, and that such regulation involves 14-3-3 proteins.