Effects of salt treatment and osmotic stress on V-ATPase and V-PPase in leaves of the halophyte Suaeda salsa

The Chenopodiaceae Suaeda salsa L. was grown under different salt concentra tions and under osmotic stress. The fresh weight was markedly stimulated by 0.1 M NaCl, 0.4 M NaCl and 0.1 M KCI and reduced by osmotic stress (PEG is o-osmotic to 0.1 M NaCl). Treatment with 0.4 M KCI severely damaged the pla nts. Membrane vesicle fractions containing tonoplast vesicles were isolated by sucrose gradient from leaves of the S. salsa plants and modulations of V-ATPase and V-PPase depending on the growth conditions were determined. We stern blot analysis revealed that V-ATPase of S. salsa consists of at least nine subunits (apparent molecular masses 66, 55, 52, 48, 36, 35, 29, 18, a nd 16 kDa). This polypeptide pattern did not depend on culture conditions. V-PPase is composed of a single polypeptide (69 kDa). An additional polypep tide (54 kDa) was detected in the fractions of NaCl-, KCl- and PEG-treated plants. It turned out that the main strategy of salt-tolerance of S. salsa seems to be an up-regulation of V-ATPase activity, which is required to ene rgize the tonoplast for ion uptake into the vacuole, while V-PPase plays on ly a minor role. The increase in V-ATPase activity is not obtained by struc tural changes of the enzyme, but by an increase in V-ATPase protein amount.