EN
Effects of exogenous gibberellic acid (GA; 10 and 100 µM) application on growth, protein and nitrogen contents, ammonium (NH₄⁺) content, enzymes of nitrogen assimilation and antioxidant system in pea seedlings were investigated under chromium (VI) phytotoxicity (Cr VI; 50, 100 and 250 µM). Exposure of pea seedlings to Cr and 100 µM GA resulted in decreased seed germination, fresh and dry weight and length of root and shoot, and protein and nitrogen contents compared to control. Compared to control, Cr and 100 µM GA led to the significant alteration in nitrogen assimilation in pea. These treatments decreased root and shoot nitrate reductase (NR), glutamine synthetase (GS) and glutamine 2-oxoglutarate aminotransferase (GOGAT) activities (except 50 µM Cr alone for GOGAT) while glutamate dehydrogenase (GDH) activity and NH₄⁺ content increased. Compared to control, the root and shoot activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX) increased (except APX activity at 250 µM Cr + 100 µM GA) while catalase (CAT), glutathione reductase (GR) and dehydroascorbate reductase (DHAR) activities were decreased (except GR at 100 µM GA alone) following exposure of Cr and 100 µM GA. Total ascorbate and total glutathione in root and shoot decreased by the treatments of Cr and 100 µM GA while their levels were increased by the application of 10 µMGA compared to Cr treatments alone. It has been reported that application of 10 µM GA together with Cr alleviated inhibited levels of growth, nitrogen assimilation and antioxidant system compared to Cr treatments alone. This study showed that application of 10 µM GA counteracts some of the adverse effects of Cr phytotoxicity with the increased levels of antioxidants and sustained activities of enzymes of nitrogen assimilation; however, 100 µM GA showed apparently reverse effect under Cr phytotoxicity.