ORIGINAL ARTICLE

Upregulation of Chloroplast Antioxidant System to Alleviate Salt Dependent Oxidative System in Rice Varieties

The chloroplast antioxidant system in pokkali (vytilla-2), kaipad (ezhome-1) and upland (koduvelliyan) rice varieties showed upregulation of enzymatic and non- enzymatic antioxidants under salt stress. The levels of hydrogen peroxide (H2O2), malondialdehyde (MDA) with respect to the lipid peroxidation of thylakoid membrane, non-enzymatic antioxidants like ascorbate (AsA), glutathione (GSH) content, enzymatic antioxidants- superoxide dismutase (SOD) and ascorbate-glutathione cycle enzymes viz, ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR) were quantified using the isolated chloroplast fraction on the 7,14 and 21 days of NaCl treatment. Chlorophyll in the NaCl treated plants decreased concomitantly with an increase in NaCl concentration. The H2O2 content and lipid peroxidation, proportionate to MDA content and the enzymatic antioxidants of the chloroplast fraction upregulated during NaCl treatment. The specific activity of the chloroplast antioxidant and ascorbate-glutathione cycle enzymes (SOD, APX, GR, MDHAR and DHAR) showed salt dependant upregulation consistently with NaCl application. Salinity induced oxidative stress alleviation by the antioxidant system in the chloroplasts of these varieties indicate the effective cooperation between antioxidant and ascorbate-glutathione cycle enzymes and holds a vital role in combating the ROS generation, thus protecting the chloroplast in the aerobic environment.