BIOCHEMICAL AND ANTIOXIDANT RESPONSES OF PADDY (ORYZA SATIVA L.) TO FLUORIDE STRESS

Fluorotoxicosis was investigated in saplings of two varieties of paddy crops, Oryza sativa L. var. Swarno and O. sativa L. var. IR-36, grown in earthen pots watered with aqueous solution containing 0, 10, 20, and 30 mg NaF/L. Eight common biochemical parameters, viz., chlorophyll, carotenoid, catalase activity, peroxidase activity, ascorbic acid, free sugar, superoxide dismutase (SOD) activity, and free amino acids were estimated from the paddy plants following harvest after 90 days. The first four parameters were estimated from the leaves only, whereas the remaining four parameters were estimated from the roots, leaves, and grains. The chlorophyll, carotenoid, free sugar, and catalase activities decreased with increasing fluoride (F) treatment. The peroxidase and SOD activities as well as the free amino acids content showed an increasing trend. Ascorbic acid initially decreased but showed a higher value for 30 mg F/L treatment. Among these paddy varieties, the IR-36 was found to be slightly more tolerant to F stress as compared to the Swarno variety. The antioxidative defense mechanisms operating in the plant cells may be responsible for the observed biochemical changes in the paddy plant parts under the F stress. The study shows that the grains produce a larger antioxidant response than the leaves and roots for the same F uptake.