Nitrogen Assimilation in Germinating Phaseolus aureus Seeds Under Saline Stress

Abstract

The developmental patterns of nitrate reductase, glutamate dehydrogenase, glutamate synthase, glutamine synthetase and soluble protein were investigated and compared in root and shoot portions of germinating green gram seeds both in the absence and presence of different concentrations of sodium chloride. The activity of all these enzymes initially increased gradually until day 4 of germination and thereafter declined under all conditions in both root and shoot tissues. In the presence of NaCl the activity levels each of nitrate reductase, glutamine synthetase and glutamate synthase were found to increase over that of the control (in absence of NaCl). Increasing the concentration of NaCl caused a further increase in the levels of these enzymes throughout the germination period in a concentration-dependent manner. On the other hand, glutamate dehydrogenase activity decreased in the presence of NaCl, and increasing concentrations of NaCl caused a further decline in the level of enzyme throughout. Saline treatment inhibited the rate of protein depletion in both shoot and root tissues throughout germination. The results indicate that the glutamine synthetase/glutamate synthase pathway of ammonia assimilation becomes operative under conditions of saline stress.