Response of Glycine max to drought stress in relation to growth parameters and some key enzymes of carbon and nitrogen metabolism

Drought stress is one of the major constraints for production and yield of soybean (Glycine max). For this reason, identifying mechanisms associated with drought tolerance in soybean is very impotent for improving and increasing drought resistance by genetic engineering methods. In this study, the effect of drought on growth traits (plant height, fresh and dry weight of shoot and also fresh and dry weight of root) and enzyme activities of isocitrate dehydrogenase (ICDH), phosphoenolpyruvate carboxylase (PEPC), malate dehydrogenase (MDH), glutamine synthetase (GS) and nitrate reductase (NR) were assessed in drought sensitive and tolerant cultivars of soybean. The results showed that growth indicators are higher in drought tolerant cultivar under water availability (control) and water deficient when compared with those of drought sensitive cultivar. An increase in the activity of ICDH was observed in both the cultivars under drought stress as compared with their respective control plants but this activity was higher in tolerant cultivar. The activities of PEPC, MDH, GS and NR were significantly decreased in drought sensitive cultivar whereas the activities of these enzymes were higher in another cultivar. In general, the results of this study showed different behavior in the activities of assayed enzymes in two sets of soybean cultivars differing in drought tolerance and also decline of the activities of these enzymes in drought sensitive cultivar due to water deficit stress may be one of the possible reasons for decreased growth of the soybean plants under drought.