NACL-INDUCED CHANGES OF NAD(P) MALIC ENZYME-ACTIVITIES IN EUCALYPTUS-CITRIODORA LEAVES

Three-month-old plants of Eucalyptus citriodora were grown in a greenh ouse iu a culture medium adjusted either to 50 or 100 mM NaCl. Sodium was rapidly absorbed by the plants and as early as 3 weeks after treat ment, an increased Na+ level was observed in shoots of 50 mM NaCl plan ts. At this stage of treatment, the growth of plants was not reduced b ut the malate metabolism was modified. The malate content decreased in leaves while the specific activities of NAD and NADP-malic enzymes in creased. The stimulation in enzyme activity was more pronounced for NA DP-malic enzyme but for both enzymes, enzyme activity diminished as ea rly as 5 weeks after treatment. The immunological study showed that th e higher activity of NAD-malic enzyme was linked to an increase in the protein amount. By contrast, a more active form of the NADP-malic enz yme mainly accounted for the higher activity of this enzyme without in volving modification in the electrophoretic mobility of the protein. T he 100 mM NaCl treatment also induced changes in the malic enzyme beha viour, the magnitude of the response however being less than for the 5 0 mM treatment. These results are discussed, mainly considering the ro le of these enzymes in the reducing power of the leaf cell.