Reactive Oxygen Species and Antioxidants Defence in Plants under Hostile Environment

Plants have to face different kinds of hostile environments including metallic ions stress, waterlogging, nutrients deficiency, and salinity during growth. Reactive oxygen species (ROS) production is a key indicator of abiotic and biotic stresses in plants. ROS is produced in cellular organelles such as chloroplast, mitochondria, peroxisome, endoplasmic reticulum, apoplast, and plasma membrane. ROS include superoxide radical (O^2-), hydrogen peroxide (H₂O₂), singlet oxygen (¹O₂), and hydroxyl radical (HO^°) overproduced in plants under different types of hostile environment. They are highly toxic and reactive in nature and react with number of important biomolecules and cause massive damages in plant physiological and biochemical parameters. The overproduction of ROS in plants results in reduction of growth, development, and yields of various valuable plants. For the protection from hostile environment, plants have a special antioxidant mechanism, which includes various enzymatic (SOD, POD, CAT, APX, GPX) and nonenzymatic (α-tocopherol, β-carotenes, carotenoids, flavonoids, total phenolic, ascorbic acid) antioxidants that counteract the hostile environment by lowering production and degradation of the ROS species and will be discussed in this chapter.