Mechanism of Free Radical Scavenging and Role of Phytohormones in Plants Under Abiotic Stresses

Abstract

Environmental stresses result in the generation of reactive oxygen species (ROS) in plants. ROS accumulate in cells and lead to the oxidation of proteins, chlorophyll, lipids, nucleic acids, carbohydrates etc. Cells have evolved intricate defense systems including enzymatic (superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductases (GR), monodehydroascorbate reductases (MSHAR), dehydroascorbate reductases (DHAR), glutathione peroxidase (GPX), guaicol peroxidase (GOPX) and glutathione-S- transferase (GST) and non-enzymatic systems such as ascorbic acid (ASH), glutathione (GSH), phenolic compounds, alkaloids, non-protein amino acids and α-tocopherol, which can scavenge the indigenously generated ROS. Plant stress tolerance mediated by antioxidants has been shown by many workers. Antioxidant resistance mechanisms may provide a strategy to enhance plant stress tolerance. Various enzymes involved in ROS-scavenging have been manipulated, over-expressed or down-regulated to add to the present knowledge and understanding of the role of antioxidant system. ROS induce the synthesis of several plant hormones, such as ethylene, salicylic acid (SA), jasmonic acid, brassinosteroids, abscisic acid (ABA) etc. These Phytohormones are required for growth and development of plants and defense responses during environmental stresses. The present review throws light on the enzymatic and non-enzymatic antioxidants in plants to enhance stress tolerance in plants and also in particular the role of brassinosteroids and ethylene during abiotic stress tolerance in plants.