Antioxidants and Antioxidative Enzymes as Potential Biomarkers for Assessing Stress in Plants

Reactive oxygen species (ROS) are an inevitable part of normal cellular metabolism in almost every known living organism. But theexcess accumulation of these radicals disturbs cellular homeostasis which can be harmful to the plant. Unlike animals who can migratethemselves away from the stress conditions, plants that are sedentary in nature have developed certain defence mechanisms to copewith the same. These mechanisms include a plethora of enzymatic and non-enzymatic antioxidants that help in scavenging free radicals.The enzymatic antioxidants include superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), guaiacol peroxidase (GPX),ascorbate peroxidase (APX), glutathione-s-transferase, monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR),and the non-enzymatic antioxidants include ascorbic acid (ASA), glutathione (GSH), tocopherols, carotenoids, etc. All these antioxidantshelp in maintaining the balance between ROS generation and scavenging by keeping their concentration below the threshold level.Numerous earlier studies have reported that only certain enzymatic antioxidants have shown increased activity in response to particularstress and likely these enzymes can be utilized as biomarkers against a multitude of biotic and abiotic stresses. In this review, we havediscussed certain enzymatic and a few non-enzymatic antioxidants which can be used for assessing stress in plants.