Reactive Oxygen Species and Antioxidant Enzymatic Systems in Plants: Role and Methods

Reactive oxygen species (ROS) are permanently generated in plastids, peroxisomes, mitochondria, cytosol and apoplast, as toxic by-products of aerobic metabolism and/or as common plant response to different biotic and abiotic stresses. Imbalance between ROS generation and safe detoxification generates oxidative stress and the accumulating ROS are harmful for plants. The cellular damages are manifested in the form of degradation of biomolecules like pigments, proteins, lipids, carbohydrates, and DNA, which ultimately lead to plant cellular death. To ensure survival, plants have developed an efficient antioxidant system of which antioxidative enzymes are the principal components, located in different sites of plant cells where ROS are generally produced. In this chapter, we emphasize on the different types of ROS, their cellular production sites, their targets, and their scavenging mechanism mediated by the antioxidant enzymatic systems. Therefore, an attempt has been made to review different in vitro assays for estimating antioxidant enzymatic activities in plants and the most cited assays in the updated literature are described.