The leaf tonoplast V-H+-ATPase activity of a C3 halophyte Suaeda salsa is enhanced by salt stress in a Ca-dependent mode

Suaeda salsa seedlings grown in Hoagland nutrient solution were treated with different concentrations of NaCl combined with two levels of Ca2+ (0 and 20 mmol/L) to study the effect of Ca2+ nutrition on the growth and activity of leaf tonoplast V-H+-ATPase. Increase of Ca2+ concentration in the solution markedly increased the relative growth quantity of S. salsa seedlings and Ca2+ and K+ concentration in the leaf cell sap under NaCl stress. The leaf V-H+-ATPase activity was significantly increased with increasing NaCl concentration under high Ca2+ application (20 mmol/L), but little changed under Ca2+ starvation (0 mmol/L). Western blot analysis showed that the leaf V-H+-ATPase of S. salsa was at least composed of A, B, D and c subunits, and their protein amounts were not affected by NaCl treatments under Ca2+ starvation (0 mmol/L) with an exception of 100 mmol/L NaCl, but increased under high Ca2+ application (20 mmol/L). There was a positive correlation between activity of V-H+-ATPase and the protein amounts of the subunits. The results suggest that Ca2+ nutrition played an important role in the salt tolerance of S. salsa, and that enhancement of V-H+-ATPase activity under salt stress was Ca2+-dependent.