Salt Responses of Carboxylation Enzymes from Species Differing in Salt Tolerance

Abstract

Enzymes which are affected by the addition of inorganic salts during in vitro assay were extracted from salt-sensitive Phaseolus vulgaris, salt-tolerant Atriplex spongiosa, and Sali-cornia australis and tested for sensitivity to NaCl. In each case malate dehydrogenase, aspartate transaminase, glucose 6-phos-phate dehydrogenase, and isocitrate dehydrogenase showed NaCl responses similar to those found for commercially avail-able crystalline enzymes from other organisms. Enzymes ex-tracted from plants grown in saline cultures showed no impor-tant changes in specific activity or salt sensitivity. Interaction of pH optima and NaCl concentrations suggests that enzymes may differ in the way they respond to salt treatment. Enzymes isolated from halophytic bacteria require high salt concentrations during assay for maximal activity (2, 3). It may be inferred that enzymes from these cells are adapted to high cytoplasmic ion concentration. In higher plants, similar adaptations of the metabolic machinery of halophytic species have been proposed to account for salt tolerance (1, 5, 7) as well as for a chloride-induced stimulation of growth in salt-accumulating halophytes (5). Optimal growth of these halo-phytes is attained with leaf sap concentrations of 200 to 300