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 complex formation between the 14-3-3 dimer and H⁺-ATPase, we assessed the effect of osmotic stress on the interaction of these proteins in suspension-cultured cells of sugar beet (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 number 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 osmotic regulation of H⁺-ATPase in the plant plasma membrane is achieved via modulation of the coupling between H⁺ transport and ATP hydrolysis, and that such regulation involves 14-3-3 proteins. Received: 10 February 2000 / Accepted: 31 March 2000