Role of the 14-3-3 proteins in the regulation of H+-ATPase activity in the plasma membrane of suspension-cultured sugar beet cells under cold stress.

All higher plants possess highly specific binding sites for fusicoccin, a metabolite of the fungus Fusicoccum amygdali Del. These sites are harboured in the plasma membranes and formed by a 14-3-3 protein dimer associated with the C-terminal autoinhibitory domain of H+-ATPase. We considered the fusicoccin binding to plasma membranes to be an indicator of complexation between the 14-3-3 dimer and H+-ATPase, we assessed the effect of cold stress on the interaction of these proteins in suspension-cultured sugar beet cells and protoplasts derived from these cells. In both objects, upon lowering the temperature to 0-4 degrees C, a portion of the cytoplasmic 14-3-3 proteins became associated with the plasma membrane, which showed an increasing amount of ATPase/14-3-3 complexes and enhanced ATPase activity. Association between ATPase and 14-3-3 resulted in a several-fold rise in the H+ efflux from protoplasts and intact cells. We suppose that regulation of the H+ pumping under changing external conditions may be based on the interaction between H+-ATPase and the 14-3-3 proteins.