Effects of hydrogen peroxide and nitric oxide on both salt and heat stress tolerance in rice

Higher plants growing in natural environments experience various abiotic stresses. H2O2 and nitric oxide (NO) free radicals are produced and cause oxidative damage to plants under various abiotic stress conditions. However, in the present study, we found that pretreating rice seedlings with low levels (<10 μM) of H2O2 or NO permitted the survival of more green leaf tissue, and of higher quantum yield for photosystem II, than in non-treated controls, under salt and heat stresses. It was also shown that the pretreatment induces not only active oxygen scavenging enzymes activities, but also expression of transcripts for stress-related genes encoding sucrose-phosphate synthase, Δ′-pyrroline-5-carboxylate synthase, and small heat shock protein 26, These results suggest that H2O2 and NO can increase both salt and heat tolerance in rice seedlings by acting as signal molecules for the response.