Reactive Oxygen Species, Oxidative Damage, and Antioxidative Defense Mechanism in Plants under Stressful Conditions

Figure 1

Schematic representation of generation of reactive oxygen species (ROS) in plants. Activation of O₂ occurs by two different mechanisms. Stepwise monovalent reduction of O₂ leads to formation of O_2•−, H₂O₂, and ^•OH, whereas energy transfer to O₂ leads to formation of ¹O₂. O_2•− is easily dismutated to H₂O₂ either nonenzymatically or by superoxide dismutase (SOD) catalyzed reaction to H₂O₂. H₂O₂ is converted to H₂O by catalase (CAT), guaiacol peroxidase (GPX), and ascorbate peroxidase (APX).