Role and Regulation of ROS and Antioxidants as Signaling Molecules in Response to Abiotic Stresses

Environmental stresses such as flood, drought, high or low temperatures, excessive soil salinity, inadequate mineral nutrients, and excess or insufficient light have adverse effects and cause damage to crop plants. Overproduction of reactive oxygen species (ROS) under stress conditions is a hallmark, comprising both free radical, superoxide radicals, hydroxyl radical, perhydroxy radical, and alkoxy radicals and nonradical (molecular) forms, like hydrogen peroxide and singlet oxygen. Production of excess ROS is very reactive in nature and interact with numerous biomolecules such as DNA, proteins, RNA, lipids, pigments, and other vital cellular molecules, leading to serious damages. The antioxidant defense mechanism of plants protects them against damage caused by environmental stress. ROS also play a key role in the acclimation process of plants to several abiotic stresses. During stress response, ROS act as important molecules and play pivotal roles in activating downstream metabolic pathways. ROS also influence the expression of a number of genes and therefore control many processes. The present chapter focuses on the description of ROS, damage caused to macromolecules by ROS, the process of ROS signaling, and antioxidant defense system under abiotic stress in plants and its role in the removal of ROS.