Physiological characterization of reproductive stage heat stress tolerance in contrasting rice genotypes

Rice is one of the important cereal crops. Two contrasting rice genotypes viz. MTU-1010 (heat tolerant) and PR-113 (heat sensitive), were exposed to heat stress at flowering stage using high temperature tunnel. Heat stress caused a significant increase in H2O2 and TBARS, while significantly decreased photosynthesis, relative water content (23-30%) and specific leaf weight (SLW) in sensitive genotype. Interestingly, MTU-1010 showed no significant changes in rate of photosynthesis, H2O2 and TBARS content, under heat stress as compared to control. However, a significant increase was recorded in activity of antioxidant enzymes like SOD, APX and GPX, both in flag leaf and spikelet tissues of MTU-1010. Besides the antioxidant defense, significantly higher SLW and RWC were documented in MTU-1010 as compared to PR-113, across the treatments. It was found that higher spikelet fertility, rate of photosynthesis and induced antioxidant system and transpiration, RWC and SLW mainly contributed for heat stress tolerance in MTU-1010 rice genotype at flowering stage as compared to PR-113. It also suggests that SLW and RWC can be useful traits in screening large panel of germplasms in future studies. However, detailed mechanistic understanding would be required to support these findings and explore the role of leaf thickness in transpiration cooling and maintaining tissue temperature under heat stress environment.