Salinity Effects on the Activity of Plasma Membrane H+and Ca2+Transporters in Bean Leaf Mesophyll: Masking Role of the Cell Wall

Net fluxes of H + and Ca 2+ were measured in the mesophyll tissue of broad bean ( Vicia faba L.) leaves and in protoplasts derived from these cells. NaCl at 90 m M enhanced H + extrusion in both protoplasts and tissue, but in different ways. Proton extrusion was inhibited by vanadate, suggesting the involvement of the plasma membrane H + -ATPase in cell responses to salinity. There was virtually no effect of NaCl on the net Ca 2+ flux in protoplasts, while in the tissue a large transient Ca 2+ efflux followed the salt treatment. Salt-induced Ca 2+ efflux was essentially independent of external Ca 2+ concentrations in the range 0.1 to 10 m M . Also, Ca 2+ flux responses were ‘saturated’ above 50 m M NaCl. It is suggested that almost all the measured Ca 2+ flux originates from Na + /Ca 2+ and H + /Ca 2+ ion exchange in the cell wall. This conclusion was supported by the results of modelling cation exchange in the cell wall.