Nitric oxide is important for sensing and survival under hypoxia in Arabidopsis

Nitric oxide (NO) is a free radical molecule that plays an important role in hypoxic stress. We studied the impact of hypoxia-induced NO production on the expression of genes and production of metabolites involved in carbon, oxygen sensing, nitrogen, and antioxidant metabolism using wild type (WT), non-symbiotic haemoglobin-overexpressing (Hb+) and nitrate reductase double mutant (nia1,2) of Arabidopsis. Futher application of NO scavenger cPTIO was used to confirm NO role. We found that imposing hypoxia leads to the increaseof NO and reactive oxygen species (ROS) levels in WT, while the reduced levels of NO and higher levels of ROS were observed in roots of Hb+ and nia1,2 mutant. Expression of the genes encoding oxygen sensing and the enzymes involved in fermentative pathways, their activities and metabolite levels were highly induced in WT suggesting that NO plays a role in the induction of fermentation. Several genes and metabolites involved in the TCA cycle were also induced in WT in comparison to Hb+ and nia mutant line suggesting that NO can accelerate TCA cycle to regenerate reducing equivalents under hypoxia. Interestingly, we found that the genes and metabolites involved in the ascorbate-glutathione cycle were modulated by NO under hypoxia. The alternative oxidasegene (AOX1A) was induced under hypoxia in WTdue to increased levels of NO rather than ROS. Futher, we found that NO improves plant survival. Overall these findings suggest that NO is a major player in plant survival under hypoxia by modulating gene expression and metabolite levels of carbon, nitrogen, oxygen sensing and antioxidant metabolism. Highlight Hypoxia-induced nitric oxide plays a central role in activation of genes and metabolites involved in fermentation, TCA cycle, nitrogen and antioxidant metabolism