Reactive Oxygen Species (ROS) and ROS Scavengers in Plant Abiotic Stress Response

The surroundings in which plants live experience fluctuations in every moment. Highly dynamic processes in the cells in response to these changes in the outside environment restore the equilibrium necessary for normal metabolism. Being sessile living beings’ plants are affected by the changes in their surroundings much more than animals, who can move themselves to a more comfortable environment. Metabolic processes produce certain bi-products that play critical roles in living cells. They present in the cells under normal conditions within a permissible level and may increase their concentration under extreme conditions like stress. Reactive oxygen species or “ROS” is one of those by-products that have multiple roles in living cells. Nearly 1–2% of the oxygen that enters the cells is converted to ROS of different types such as singlet oxygen, superoxide radical, hydroxide radical, and hydrogen peroxide, which are inevitable components in activating many molecular pathways in cells. The sensitive balance in terms of the amount of ROS present in a cell at a time is taken care of by a group of molecules known as ROS scavengers, which are part of the antioxidant machinery in the cells. While the redox signalling pathways mediated by the ROS under normal conditions are beneficial for plant growth, and development, the pathways activated by the ROS under stress conditions have a negative effect on plants. Even though the ROS induces the ROS scavenger’s production and activity, depending on the intensity and duration of the stress it may be beneficial or ineffective. This chapter discusses about different types of ROS and ROS scavengers, the conditions leading to their origin, the role played by them under normal and stressed conditions, and the major organelles involved in the ROS signalling pathways.