Increased vacuolar and plasma membrane H⁺-ATPase activities inSalicornia bigeloviiTorr. in response to NaCl

The halophyte Salicornia bigelovii Torr. shows optimal growth and Na+ accumulation in 200 mM NaCl and reduced growth under lower salinity conditions. The ability to accumulate and compartmentalize Na+ may result, in part, from stimulation of the H+ -ATPases on the plasma membrane (PM-ATPase) and vacuolar membranes (V-ATPase). To determine if these two primary transport systems are involved in salt tolerance, shoot fresh weight (FW) and activity of the PM- and V-ATPases from shoots in Salicornia grown in 5 and 200 mM NaCI were compared. Higher PM-ATPase activity (60%) and FW (60%) were observed in plants grown in 200 mM NaCI and these stimulations in growth and enzyme activity were specific for Na+ and not observed with Na+ added in vitro. V-ATPase activity was significantly stimulated in vivo and in vitro (26% and 46%, respectively) after exposure to 200 mM NaCl, and stimulation was Na+ -specific. Immunoblots indicated that the increases in activity of the H+ -ATPases from plants grown in 200 mM NaCI was not due to increases in protein expression. These studies suggest that the H+-ATPases in Salicornia are important in salt tolerance and provide a biochemical framework for understanding mechanisms of salt tolerance in plants.