Heat tolerance in rice mutants is associated with reduced accumulation of reactive oxygen species

Four mutants induced by ethylmethane sulphonate (N22-H-dgl56, N22-H-dgl101, N22-H-dgl162 and N22-H-dgl219) with conspicuous dark green leaves were identified in the drought and heat-tolerant rice cultivar Nagina22 (N22) when screened under prolonged drought and heat conditions in field. During dark-induced senescence, these mutants maintained higher chlorophyll and carotenoid concentrations, and photochemical efficiency of photosystem 2 in comparison with N22. Following heat treatment, these mutants accumulated less reactive oxygen species (assayed by histochemical staining for H2O2 and superoxide radicals) and maintained higher chlorophyll content than N22.