Proton pumping in growing part of maize root: its correlation with 14-3-3 protein content and changes in response to osmotic stress

The spatial pattern of mitotic activity, cell elongation, rate of H+ fluxes, and 14-3-3 protein content were determined in Zea mays roots. We found that the regions along the apical part of the growing root conversely differ in their proton pumping activity. Higher rate of H+ efflux coincides with higher growth rate and correlates with increased 14-3-3 protein content in membrane preparations. The segment consisting of the root cap and the apical part of the meristem exerts net inward proton pumping, which can be inverted under fusicoccin treatment or osmotic stress. In the latter case, this inversion is accompanied by accumulation of 14-3-3 protein in plasma membranes. The results obtained highlight 14-3-3 protein as an obvious candidate for the fine regulation of plasma membrane H+-ATPase in root apex.