Silicon mediates arsenic tolerance in rice (Oryza sativa L.) through lowering of arsenic uptake and improved antioxidant defence system

Abstract

Arsenic (As) contamination of paddy rice in South and South-East Asia has raised much concern as rice is the subsidence diet for millions. Two contrasting rice (Oryza sativa L.) cultivars i.e. Triguna (As tolerant) and IET-4786 (As sensitive) were grown hydroponically to study the effect of silicon (Si) supplementation on As accumulation, growth, oxidative stress and antioxidative defence system in shoots during arsenite [As(III)] stress. Rice seedlings were exposed to three As(III) levels (0, 10 and 25μM) and three silicic acid levels (0, 0.5 and 1mM Si) in solution culture experiments. Addition of 1mM Si during As(III) exposure significantly lowers shoot As accumulation in both the cultivar, but more prominently in Triguna (P≤0.01) than IET-4786 (P≤0.05). However, addition of Si during As(III) stress had no significant effect on shoot length and dry weight (P<0.01) of both the cultivars, compared to their As(III) treated plants. In contrast to IET-4786 (P≤0.05), Triguna tolerated As induced oxidative stress through elevated level of cysteine, enhanced antioxidant enzymes activities and their isozymes. Upon Si supplementation lower conglomeration of oxidative stress parameters viz., superoxide and peroxide radicals, lipid peroxidation and electrolyte leakage coincides with increased antioxidants activities and enhanced level of thiols, more effectively in shoots of Triguna than IET-4786 during As(III) stress (P≤0.05). In conclusion, 1mM Si addition, significantly ameliorates As induced oxidative stress in Triguna cultivar by lowering the As accumulation and improving antioxidant and thiolic system compared to IET-4786, implying genotypic differences with Triguna being less susceptible to stress dependent membrane lipid peroxidation.