Nitric oxide triggered defense network in wheat: Augmenting tolerance and grain-quality related traits under heat-induced oxidative damage.

Highlights • The effect of heat stress can be alleviated by nitric oxide (150 μM) treatment in wheat. • Nitric oxide triggers the expression of SAGs and enhances the scavenging potential of wheat under heat stress. • Nitric oxide improves the quality of wheat grain by enhancing the accumulation of gliadin protein and starch. • Nitric oxide maintains the quality of starch in wheat grain by reducing the amylolytic activity under heat stress. • Nitric oxide enhances the accumulation of soluble protein, free amino acids and osmolyte in developing grains under HS. Abstract Heat stress (HS) drastically reduces the yield and quality of wheat grains. High temperature during critical stages (pollination and grain-filling) causes improper fertilization and formation of defragmented granules and shriveled seeds. Hormones and signaling molecules modulates the tolerance potential of the plants under stress. Nitric oxide (NO) is an important signaling molecule involved in triggering diverse physiological and biochemical processes under adverse conditions. Here, we studied the effect of sodium nitroprusside (SNP) (150 μM set based on pilot experiment) on heat stress-tolerance and grain quality related traits of two contrasting wheat cultivars Raj3765 as thermotolerant and HD2932 as thermosusceptible under differential HS (T 1 - 30 °C, 1 h; T 2 - 38 °C, 1 h), as compared to control (22 ± 2 °C) at different stages of growth. The expression of many important stress-associated genes (previously identified through Transcriptome sequencing) was observed upregulated in response to NO and HS; small HSP17 showed maximum fold increase in Raj3765. Similarly, the networks of antioxidant enzymes (SOD, CAT, and GPX) were observed triggered in response to NO, HS and NO + HS treatment in Raj3765 than HD2932. The accumulation of proline and free amino acid in cytoplasm were also reported higher under NO and HS treatment respectively in Raj3765, as compared to HD2932. Grain quality related traits like carbohydrate (starch) and proteins (gliadin) were observed higher in response to NO under HS in Raj3765. Heat stress was observed to increase the activities of α/β amylases in developing grains involved in degrading the starch quality. NO was observed to decrease the amylolytic activity in both the cultivars; very low amylolytic activity was observed in thermotolerant, as compared to thermosusceptible cultivars. Exogenous application of NO (150 μM) at different stages can be used as inexpensive technology for mitigating the problem of terminal HS in wheat – a farmer friendly approach for maintaining the quality of grains under present threat of global climate change. [ABSTRACT FROM AUTHOR]