A field experiment was conducted to study the response of antioxidant enzymes to oxidative damage caused by heat stress induced by changing dates of transplanting in two rice (Oryza sativa L.) genotypes viz., ‘N22’ (heat tolerant) and ‘IR8’ (heat susceptible). During grain filling period, constitutive level of antioxidative enzymes viz., superoxide dismutase, catalase, ascorbate peroxidase, was found to be , and higher respectively, while the content of non-enzymatic antioxidants viz., ascorbate and proline was and higher respectively, in ‘N22’ than in ‘IR8’ under heat stress encountered during early transplanting. In contrast, the hydrogen peroxide and malondialdehyde content were and higher in ‘IR8’ during early transplanting. Heat stress resulted in significant reduction of chlorophyll content during early transplanting in both the genotypes though the reduction was less in ‘N22’ () as compared to ‘IR8’ (). The increased and timely response of antioxidant enzymes along with the non enzymatic antioxidants is suggestive of their significant role in development of tolerance exhibited by the cultivar ‘N22’ under heat stress conditions. | Variation in antioxidant responses in rice (Oryza sativa L.) genotypes differing in sensitivity to heat stress
