THE INVOLVEMENT OF A VANADATE-SENSITIVE ATPASE IN PLASMA-MEMBRANES OFA SALT-TOLERANT CYANOBACTERIUM

Plasma membranes of the marine cyanobacterium Spirulina subsalsa were tested for ATPase activity, and for involvement in salt stress. Transi tion of cells from saline to hypersaline medium enhances the respirato ry activity associated with extrusion of Na+ and Cl-, and persisting s alt stress induces synthesis of respiratory enzymes in the plasma memb ranes. The membranes possess an ATPase, specific for ATP and Mg2+ and sensitive to orthovanadate and dicyclohexylcarbodiimide. Immunoblot an alysis of plasma membrane polypeptides from Spirulina subsalsa with an ti-Arabidopsis H+-ATPase serum identified a single polypeptide of 100 kDa, which cross-reacted with the antibodies. An unusual feature of th is ATPase is a specific stimulation by Na+ ions. Prolonged adaptation of S. subsalsa cells to hypersaline conditions induced an increase in ATPase activity in subsequent plasma membrane preparations, as well as a higher content of the 100 kDa polypeptide. It is suggested that the ATPase investigated is an H+-pump, which is involved in extrusion of Na+ and in conferring resistance to salt stress.