Biosynthesis of nitric oxide and cross talk with other signaling molecules in abiotic stress tolerance

Among reactive nitrogen species, nitric oxide (NO) is an important secondary messenger next to reactive oxygen species (ROS) produced under abiotic stress. NO is a small, colorless simple gas but is an important redox active molecule in plants as it has the potential in regulating a wide range of biological processes. Under stress conditions, endogenous synthesis of NO takes place in different plant cell organelles and its accumulation correlates with stress tolerance as it counteracts ROS production by stimulating antioxidant defense response in plants. Several studies have suggested that exogenous application of NO alleviates stress tolerance in most of plant species, although its exact role is unclear. In view of this, an effort has been made in this review to trace steps of NO involvement in different organelles to upgrade the current knowledge. Here, we first discuss the biosynthesis of NO, its sources, targets, signaling pathways, and then advances in NO-mediated biochemical and physiological changes that occur in response to various abiotic stress conditions are also discussed. Furthermore, a brief focus is carried out to determine the mechanism of NO activation in response to ROS production.