Increased vacuolar and plasma membrane H⁺-ATPase activities in Salicornia bigelovii Torr. in response to NaCl

The halophyte Salicornia bigelovii Torr, shows optimal growth and Na⁺ accumulation in 200mM 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 NaCl were compared. Higher PM-ATPase activity (60%) and FW (60%) were observed in plants grown in 200 mM NaCl 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.