Salt modulation of vacuolar H+-ATPase and H+-pyrophosphatase activities inVigna unguiculata

Salt modulation of the tonoplast H+-pumping V-ATPase and H+-PPase was evalu ated in hypocotyls of Vigna unguiculata seedlings after 3 and 7 days of tre atment. In 9-day-old seedlings, treatment with 100 mmol/L NaCl decreased th e proton transport and hydrolytic activities of both the V-ATPase and the H +-PPase. Alter 7 days, the proton transport and hydrolysis activities of th e V-ATPase were higher, while the H+-PPase activities were lower in seedlin gs. Western blot analysis of A- and B-subunits oi V-ATPase revealed that th e protein content of the two subunits varied in parallel with their activit ies, i.e, to a higher activity corresponded a higher protein content of the subunits and vice versa. Contrarily, Western blot analysis of Hi-PPase lev els failed to show any correlation with PPase activity, suggesting a partia l enzyme inactivation. The results indicate that salt stress induces V-ATPa se expression in L! unguiculata with concomitant enhancement of its activit y as a homeostatic mechanism to cope with salt stress. Under the same condi tions PPase is inhibited.