ABSTRACT
Reactive oxygen species (ROS) are produced in substantial amount in plants under abiotic stress. These ROS are the byproducts of various metabolic reactions such as respiration and photosynthesis. Plants tend to produce minimal levels of ROS under normal conditions, but their cellular levels rise when they face abiotic stress. ROS also act as signaling molecules. However, there is a consensus among researchers that greater cellular levels of ROS cause oxidative damage to plants. An antioxidant system comprising enzymatic and non-enzymatic components exists in plants that readily scavenge the ROS and thereby protects plants from oxidative damage. A non-enzymatic component in plants includes ascorbic acid, tocopherols, glutathione, phenolics, flavonoids and carotenoids that play a critical role in plants under abiotic stress. Non-enzymatic antioxidants interact with important physiochemical processes in plants and induce tolerance against abiotic stress. Researchers have also supplemented these compounds exogenously in plants under abiotic stress and found enhanced tolerance in treated plants. This chapter describes in detail the mechanism of action of non-enzymatic antioxidants and also summarizes the literature review that deals with the exogenous application of non-enzymatic antioxidants.
