Salt-induced Na+H+ antiport in root plasma membrane of a glycophytic and halophytic species of tomato

Plasma membrane and tonoplast vesicles were isolated from roots of both the glycophytic cultivated tomato and its halophytic wild relative, Lycopersicon cheesmanii, grown under control and saline conditions and found to have higher rates of quench and rates of ATP hydrolysis than when grown under saline conditions.

Abstract

Plasma membrane and tonoplast vesicles were isolated from roots of both the glycophytic cultivated tomato, Lycopersicon esculentum (Mill, cv. Heinz 1350) and its halophytic wild relative, Lycopersicon cheesmanii (Hook, C.H. Mull, ecotype 1401) grown under control and saline conditions. MgATP-dependent proton transport was measured by determining the rate of quench of quinacrine fluorescence. Rates of quench and rates of ATP hydrolysis were higher for both the plasma membrane and tonoplast from both species when grown under saline conditions. When ATPase activity was measured, the degree of stimulation of ATP hydrolysis in the presence of KCl, NaCl, and choline chloride was similar for the plasma membrane from control and salt grown plants. However, NaCl gave lower rates of proton transport than did KCl or choline chloride for the plasma membrane of both L. esculentum and L. cheesmanii grown under saline conditions. This may be interpreted as evidence of Na+H+ antiport. A pH gradient (acid interior) was formed in vesicles by adding MgATP. After the establishment of a proton gradient, the effect of cations on proton efflux was estimated by adding EDTA to chelate the Mg2+. Fluorescence recovery rate was used as an indication of the rate of proton efflux. The addition of Na+ enhanced fluorescence recovery compared to K+ in plasma membranes from both species grown under saline conditions. Addition of K+ and valinomycin to the assay media did not affect Na+H+ exchange, nor did addition of amiloride. No evidence was found for a Na+H+ antiport mechanism in the tonoplast of either L. esculentum or L. cheesmanii regardless of growth conditions.