Varietal Differences in Growth, Sodium Uptake and Antioxidant Responses of Rice Seedling to Salinity Stress

Abstract

The growth rate, leaf sodium uptake and possible involvement of activated oxygen species in the mechanism of damage by NaCl stress was studied in four varieties of rice (Oryza sativa L.) exhibiting different sensitivities to NaCl. The 3-week-old rice seedlings were subjected to 0, 6 and 12 dS m −1 (equivalent to 0, 60 and 120 mM NaCl) salinity levels for 1-week after which antioxidant capacities, growth rate and Na+ uptake of the leaves were analyzed. High salinity treatment caused a decrease in growth rate in all the varieties tested except Pokkali. Varieties that are considered to be salt-sensitive, Hitomebore, IR28 and Bankat, exhibited a decrease in superoxide dismutase activity and an increase in peroxidase activity under high salinization. These varieties also exhibited increase in lipid peroxidation and electrolyte leakage as well as higher Na+ accumulation in the leaves under salt stress. The salt-tolerant variety Pokkali, however, showed only slight increase and decrease in superoxide dismutase and peroxidase activity, respectively, and virtually unchanged lipid peroxidation, electrolyte leakage and Na+ accumulation upon salinization. These results indicate that free radical-mediated damage of membrane may play an important role in the cellular toxicity of NaCl in rice seedlings and that salt-tolerant varieties exhibit protection mechanism against increased radical production by maintaining the specific activity of antioxidant enzymes.

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