Modification of chromium (VI) phytotoxicity by exogenous gibberellic acid application in Pisum sativum (L.) seedlings

Effects of exogenous gibberellic acid (GA; 10 and 100 mu M) 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 mu M). Exposure of pea seedlings to Cr and 100 mu M 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 mu M 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 mu M 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 mu M Cr + 100 mu M GA) while catalase (CAT), glutathione reductase (GR) and dehydroascorbate reductase (DHAR) activities were decreased (except GR at 100 mu M GA alone) following exposure of Cr and 100 mu M GA. Total ascorbate and total glutathione in root and shoot decreased by the treatments of Cr and 100 mu M GA while their levels were increased by the application of 10 mu M GA compared to Cr treatments alone. It has been reported that application of 10 mu M 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 mu M 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 mu M GA showed apparently reverse effect under Cr phytotoxicity.