Abstract
Net fluxes of H+and Ca2+were measured in the mesophyll tissue of broad bean (Vicia faba L.) leaves and in protoplasts derived from these cells. NaCl at 90m 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 Ca2+flux in protoplasts, while in the tissue a large transient Ca2+efflux followed the salt treatment. Salt-induced Ca2+efflux was essentially independent of external Ca2+concentrations in the range 0.1 to 10m M. Also, Ca2+flux responses were ‘saturated’ above 50m M NaCl. It is suggested that almost all the measured Ca2+flux originates from Na+/Ca2+and H+/Ca2+ion exchange in the cell wall. This conclusion was supported by the results of modelling cation exchange in the cell wall.
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