Overproduction of ROS: underlying molecular mechanism of scavenging and redox signaling

Abstract Reactive oxygen species (ROS) are the by-product of partially reduced molecular oxygen during aerobic metabolism, thus inducing oxidative stress aggravates cellular damage and ultimately cell death. In plants, ROS are produced by an oxidation-reduction reaction localized in different cellular compartments. Various biotic and abiotic factors result in excessive ROS production, which includes mainly singlet oxygen (1O2), superoxide anion (O2•−), hydrogen peroxide (H2O2), hydroxyl radical (OH•), and perhydroxyl radical (HO2•) that cause damage to DNA, proteins, and lipids. Plants possess the unique antioxidant (enzymatic and nonenzymatic) defense system that works in coordination to detoxify and quench the ROS cytotoxicity and protects plants from lipid peroxidation. Besides their destructive role, ROS play a crucial role as a secondary messenger in various cellular and biological processes such as growth and development, and conformant of biotic and abiotic stress tolerance in plants. ROS functioning mainly depends on the regulatory mechanism of respiratory burst oxidase (RBOH) and its homologs. These enzymes are known to involve in various signaling pathways in different tissues that are activated under fluctuation environmental stimuli. This chapter mainly describes the different types and production sites of ROS, enzymatic, and nonenzymatic scavenging mechanism, and ROS role as redox signaling in regulating abiotic stress response in plants.