Mechanisms of nitric oxide crosstalk with reactive oxygen species scavenging enzymes during abiotic stress tolerance in plants.

Nitric oxide (NO) acts in a concentration and redox-dependent manner to counteract oxidative stress either by directly acting as an antioxidant through scavenging reactive oxygen species (ROS), such as superoxide anions (O(2)(-)*), to form peroxynitrite (ONOO(-)) or by acting as a signaling molecule, thereby altering gene expression. NO can interact with different metal centres in proteins, such as heme-iron, zinc-sulfur clusters, iron-sulfur clusters, and copper, resulting in the formation of a stable metal-nitrosyl complex or production of varied biochemical signals, which ultimately leads to modification of protein structure/function. The thiols (ferrous iron-thiol complex and nitrosothiols) are also involved in the metabolism and mobilization of NO. Thiols bind to NO and transport it to the site of action whereas nitrosothiols release NO after intercellular diffusion and uptake into the target cells. S-nitrosoglutathione (GSNO) also has the ability to transnitrosylate proteins. It is an NO˙ reservoir and a long-distance signaling molecule. Tyrosine nitration of proteins has been suggested as a biomarker of nitrosative stress as it can lead to either activation or inhibition of target proteins. The exact molecular mechanism(s) by which exogenous and endogenously generated NO (or reactive nitrogen species) modulate the induction of various genes affecting redox homeostasis, are being extensively investigated currently by various research groups. Present review provides an in-depth analysis of the mechanisms by which NO interacts with and modulates the activity of various ROS scavenging enzymes, particularly accompanying ROS generation in plants in response to varied abiotic stress.