Oxidative Stress in Plants and Its Management

Abstract

We all live in an oxygen-rich environment which has to deal with the danger of oxidative stress. During normal cell metabolism, reactive oxygen species (ROS) are constantly produced, mainly by respiratory and photosynthetic components. These species mainly include superoxide radicals (O2 −), singlet oxygen (1O2), hydrogen peroxide (H2O2), and hydroxyl radical (OH−). The others are hydroperoxyl radical (HO2˙), alkoxy radical (RO˙), peroxyl radicals (ROO˙), and excited carbonyl (RO). But during stress conditions like salinity, drought, metal toxicity, herbicides, fungicides, air pollutants, hypoxia, and abnormal conditions of light, temperature, and topography, ROS are produced in excess amount. These highly reactive molecules can react with many cellular biomolecules and other components and damage DNA, proteins, and lipids. Thus, their concentration has to be tightly controlled. To counter the deleterious effects of ROS, aerobic organisms are equipped with antioxidant systems to scavenge ROS from the cells. Enzymatic antioxidants are mainly superoxide dismutase (SOD), catalase, ascorbate peroxidase, glutathione peroxidase, glutathione S-transferases, and peroxiredoxin, while the nonenzymatic antioxidants are mainly ascorbate, glutathione, proline, tocopherol, flavonoids, and carotenoids. These antioxidants protect against the oxidative damage by inhibiting or quenching free radicals and ROS. When the balance between the production of ROS and the quenching activities of antioxidants is disturbed, the cell faces the risk of oxidative stress and damage. These ROS creating stresses are numerous and often species or area specific. These stresses cause significant crop losses. There is a growing need to develop crops which can be resistant to the effects of various oxidative stresses. One such way is to develop transgenic plants overexpressing one or more antioxidants, which can confer resistance towards particular stress. Another way is to develop mutants which are resistant towards certain stresses.