Salt Tolerance in the Halophyte, Suaeda maritima (L.) dum.: Properties of Malic Enzyme and PEP carboxylase

Malic enzyme and phosphenol pyruvate carboxylase activities have been isolated and characterized from the shoots of Suaeda maritima plants grown in culture solution (with and without NaCl) or in tap water. The enzymes isolated from the latter showed increases in both specific activity and Km values in comparison with plants grown in culture solution: however, the addition of NaCl to the culture solution had no significant effect on either enzyme. Malate levels were high in plants grown in tap water, reduced by an ordeT of magnitude by the addition of culture solution and then halved by the addition of NaCl. Both enzymes were inhibited in vitro by NaCl, although the addition of high concentrations of betaine and proline to the assay medium did not further inhibit enzyme activity. The significance of these results is discussed in relation to the proposed role of betaine and proline as cytoplasmic osmoregulators.