Differential antioxidative response of ascorbate glutathione pathway enzymes and metabolites to chromium speciation stress in green gram (Vigna radiata (L.) R.Wilczek. cv CO 4) roots

The response of the antioxidant enzymes and metabolites of the ascorbate glutathione pathway to oxidative stress caused by equal concentration (50 muM) of Cr(III) and Cr(VI) was studied in 15-day-old seedlings of green gram (Vigna radiata (L.) R.Wilczek. cv CO 4) for 5 days after imposition of stress. Significant increase in lipid peroxidation and H2O2 generation was seen 5 h after stress in Cr(VI) as against 12 h in Cr(III)-treated plants. High rate of uptake and translocation of Cr was seen in the first 12h of treatment with roots retaining 80 times more Cr than the shoots in both the speciation. No significant increase in catalase (CAT) activity and monodehydroascorbate reductase (MDHAR) was observed under Cr(III). Superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities increased under Cr(VI) after 12 and 4 h, respectively. Under Cr(VI) stress there was a steep increase of 194.6 nM g(-1) FW in the ascorbic acid (AA) content between 5 and 24 h of treatment. In contrast to reduced glutathione (GSH) content, which reduced after 24 It after treatment, oxidized glutathione (GSSG) increased steadily through the course of the experiment under both speciation. The rate of decline in the GSH/GSSG ratio was much faster in Cr(III) than Cr(VI). Results suggest differential response to AA and H2O2 signaling by Cr(III) and Cr(VI) and that AA in combination with APX was more effective in mitigating oxidative stress as against the role of GSH as an antioxidant. (C) 2004 Elsevier Ireland Ltd. All rights reserved.