Selective Effect of Salt Stress on the Activity of Two ATPases in the Cell Membrane of <italic>Nostoc muscorum</italic>

Abstract

ATPase activity in the cell membrane of a salt-stressed cyanobacterium, Nostoc muscorum M-14, was examined cytochemically by three different staining protocols. Application of Hulstaert's method resulted in distinct precipitation of the reaction products of ATPase inside the cell membrane exclusively. No reaction products were formed when ATP was replaced by GTP or when dicyclohexylcarbodiimide or N-ethylmaleimide was present in the reaction mixture. By contrast, low levels were detectable after the reaction in the presence of ouabain. Bafilomycin did not affect the formation of products. Mayahara's method, which is considered to demonstrate the reaction of Na+,K+-ATPase activity, revealed the presence of a ouabain-sensitive Na+,K+-ATPase in the cell membrane, while Wachstein-Meisel's method revealed the presence of an ATPase activity that was resistant to ouabain. It appears, therefore, that cell membranes of Nostoc muscorum contain both ouabain-sensitive ATPase and ouabain-insensitive ATPase. Comparison of the staining profiles of salt-stressed cells with those of control cells suggested that a high-salt environment activates the ouabain-sensitive Na+,K+-ATPase, which seems likely to be involved in the efflux of Na+ ions.