Modification of Osmolytes and Antioxidant Enzymes by 24-Epibrassinolide in Chickpea Seedlings Under Mercury (Hg) Toxicity

The effects of 24-epibrassinolide (EBL, 10(-6) M) on mitigation of mercury (Hg, 15 mu M and 30 mu M HgCl2) toxicity on growth, physio-biochemical attributes, and antioxidant enzymes in chickpea (Cicer arietinum L.) were evaluated. Mercury (Hg)-treated plants showed reduced growth and leaf pigment content in a concentration-dependent manner, but this effect was significantly ameliorated by EBL application. Exogenously applied EBL enhanced the accumulation of proline and glycine betaine (GB) in control as well as in Hg-treated plants reflecting the positive effects of EBL on leaf's relative water content (RWC) in the plants. EBL supplementation reduced the production of hydrogen peroxide, and hence, lipid peroxidation that ultimately provided membrane stability, thereby aiding in reducing electrolyte leakage induced by Hg toxicity. Application of EBL significantly improved the activities of antioxidant enzymes including SOD, CAT, GST, and GPX, thereby resulting in optimization of the ascorbate-glutathione pathway by improving the contents of electron donors and redox components, ascorbate (AsA), and glutathione (reduced as well as oxidized), which might have contributed to protecting the photosynthetic electron transport chain from Hg-induced oxidative stress. Considerable improvement in the uptake of essential elements was also obvious in EBL-treated plants. In conclusion, Hg stress induced adverse effects on growth and development of chickpea seedlings; however, EBL-treated seedlings showed restored growth through modulation of biochemical parameters and enzymatic and nonenzymatic antioxidants.