ON THE POSSIBLE ROLE OF FUSICOCCIN-BINDING PROTEINS IN PLANT ADAPTATION TO STRESS

Protoplasts alkalizing the cytoplasm when bound to fusicoccin (FC) wer e isolated from the suspension culture of sugar beet (Beta vulgaris L. ) cells. Two kinds of FC-binding sites, which differed in their affini ty for FC by two orders of magnitude, were detected on plasma membrane s of isolated protoplasts. The balance between FC-binding proteins of different affinity observed at the standard conditions changed in favo r of high-affinity proteins under the conditions of cytosol acidificat ion. This shift was reversible and occurred in the narrow physiologica l range of pH values. It is supposed that the changes in affinity may be accounted for by the conformational changes generated in FC-binding proteins by the shifts in cytosolic pH. A possible scheme for the con trol of H+-ATPase activity of the plasma membrane by FC-binding protei ns in stress-affected plants is proposed.