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 Ca²⁺were measured in the mesophyll tissueof broad bean (Vicia faba L.) leaves and in protoplasts derivedfrom these cells. NaCl at 90 m M enhanced H⁺extrusion in bothprotoplasts and tissue, but in different ways. Proton extrusionwas inhibited by vanadate, suggesting the involvement of theplasma membrane H⁺-ATPase in cell responses to salinity. Therewas virtually no effect of NaCl on the net Ca²⁺flux in protoplasts,while in the tissue a large transient Ca²⁺efflux followed thesalt treatment. Salt-induced Ca²⁺efflux was essentially independentof external Ca²⁺concentrations in the range 0.1 to 10 m M. Also,Ca²⁺flux responses were ‘saturated’ above 50 m MNaCl. It is suggested that almost all the measured Ca²⁺fluxoriginates from Na⁺/Ca²⁺and H⁺/Ca²⁺ion exchange in the cellwall. This conclusion was supported by the results of modellingcation exchange in the cell wall. Copyright 2000 Annals of BotanyCompany Salinity, membrane transporters, wall ion exchange, proton, calcium, Vicia faba