Recent Developments in Enzymatic Antioxidant Defence Mechanism in Plants with Special Reference to Abiotic Stress

SIMPLE SUMMARY: Higher plants face a variety of stress conditions. There are a number of different antioxidant enzymes that help plants to cope with these stresses. During stresses, SOD catalyses the removal of •O(2)(−) by dismutating it into O(2) and H(2)O(2). The CAT converts the H(2)O(2) into water and O(2). POX works in the extracellular space for scavenging H(2)O(2). Plant GPX catalyses the reduction of H(2)O(2) and HO(2) to water and lipid alcohols, respectively. GR catalyses the reduction of oxidised glutathione (GSSG; dimeric) to reduced glutathione (GSH; monomeric). APX utilises ascorbate as a specific electron donor to scavenge H(2)O(2) to water. ABSTRACT: The stationary life of plants has led to the evolution of a complex gridded antioxidant defence system constituting numerous enzymatic components, playing a crucial role in overcoming various stress conditions. Mainly, these plant enzymes are superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), glutathione peroxidase (GPX), glutathione reductase (GR), glutathione S-transferases (GST), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), and dehydroascorbate reductase (DHAR), which work as part of the antioxidant defence system. These enzymes together form a complex set of mechanisms to minimise, buffer, and scavenge the reactive oxygen species (ROS) efficiently. The present review is aimed at articulating the current understanding of each of these enzymatic components, with special attention on the role of each enzyme in response to the various environmental, especially abiotic stresses, their molecular characterisation, and reaction mechanisms. The role of the enzymatic defence system for plant health and development, their significance, and cross-talk mechanisms are discussed in detail. Additionally, the application of antioxidant enzymes in developing stress-tolerant transgenic plants are also discussed.