Evaluation of physiological and biochemical responses of rice (Oryza sativa L.) varieties to salt stress

A hydroponics study for salt tolerance was conducted in ten rice varieties, differing in salt tolerance viz., TRY 1, TRY(R)2, TRY 3 (TNAU, Coimbatore), CSR 13, CSR 27, CSR 30, CSR 36 (CSSRI, Karnal), Ezhome-1 and Ezhome-2 (KAU, Trissur) and IR 29 at seedling stage. The influence of NaCl at 0, 60 and 120 mM concentrations on seedling dry weight, shoot length, photosynthetic rate, superoxide dismutase activity, ascorbate peroxidase activity, malondialdehyde concentration and Na⁺/K⁺ ratio was investigated. Increasing salt levels reduced the photosynthetic rate, dry weight and shoot length substantially in rice varieties with greater reduction in the sensitive variety IR 29. The activities of SOD and APX were enhanced in tolerant varieties which contributed to lower lipid peroxidation. The results indicate that a low Na⁺/K⁺ ratio along with increased activity of antioxidant enzymes and lower lipid peroxidation may contribute to the NaCl tolerance mechanism in rice varieties.