Electrostatic changes in root plasma membrane of glycophytic and halophytic species of tomato

We investigated the effect of salt stress on the electrostatic properties of plasma membrane vesicles obtained from both the glycophytic, cultivated tomato, Lycopersicon esculentum (Mill, cvs. Heinz-1350 and VF 36) and the halophytic, wild species, L. cheesmanii (Hook, C.H. Mull, ecotype 1401) grown under control and saline conditions to determine if there exists a difference in the modulation of the membrane surface charge between the glycophytic and halophytic tomato. In agreement with earlier findings, fluorescence titration of vesicles indicated that salinity stress resulted in the modulation of the plasma membrane surface potential to more positive values in the glycophytic tomato species. However, a much smaller shift was measured in the halophytic tomato. Membrane surface potentials (Ψ0) of −20.0 and −7.6 mv were calculated for control and salt-stressed vesicles from the glycophytic Heinz-1350 cultivar, respectively, and −22.0 and −3.3 mv, respectively, from the glycophytic VF 36 cultivar. For the halophytic species, Lc-1401, we measured membrane surface potentials (Ψ0) of −24.8 and −19.7 mv for control and salt-stressed vesicles, respectively. BTP-Cl− stimulation of ΔpH was greater in vesicles isolated from control roots obtained from the wild Lc-1401 as compared with the cultivated Heinz-1350. However, the reverse was true in vesicles isolated from salt-stressed roots. Cl− stimulated proton pumping to a greater degree in vesicles from Heinz-1350 than Lc-1401. Both K+ or Na+ (added as K+- or Na+-Mes along with 100 mM BTP-Cl−) stimulated H+-pumping activity in plasma membrane vesicles from both Heinz-1350 and Lc-1401. In most cases, K+ stimulation of H+-pumping activity was higher in vesicles isolated from salt-stressed than from non-stressed plants.