SALT STRESS INCREASES FERREDOXIN-DEPENDENT GLUTAMATE SYNTHASE ACTIVITY AND PROTEIN LEVEL IN THE LEAVES OF TOMATO

Ferredoxin-dependent glutamate synthase (EC 1.4.7.1) catalyzes an esse ntial step in the pathway of glutamate biosynthesis. Exposing detached tomato (Lycopersicon esculentum) leaves for 6 h to 12 g l(-1) NaCl re sulted in a significant two-fold increase in the activity of ferredoxi n-dependent glutamate synthase extracted from the leaves. Western blot studies demonstrated that salt treatment also increased the ferredoxi n-dependent glutamate synthase content of the leaves. A similar effect of salt on the concentration of this enzyme was found in the leaves o f hydroponically-grown tomato plants. The induction of ferredoxin-depe ndent glutamate synthase under salt stress may provide the glutamate r equired for the proline synthesis which is a common response to salt s tress.