Antioxidant Defence: A Key Frontier in Conferring Cadmium Tolerance in Plants

Under favourable circumstances, reactive oxygen species (ROS) is frequently produced at safe levels and controlled by multifarious networks. The delicate equilibrium between ROS (O2•−, H2O2, 1O2, •OH) origination and ROS scavenging is constantly disordered by environmental stress factors like drought, heat, salinity and heavy metal. The heavy metal ions including Cd extensively disrupt redox homeostasis making ROS extremely deadly and impair cellular homeostasis. This in turn indicates scanty plant health and crop output. To ensure the existence and adapt to such Cd mediated stress conditions, plants have amalgamated antioxidant machinery having two well equipped arms, enzymatic superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), glutathione peroxidase (GPX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR) and non-enzymatic ascorbic acid (AsA), glutathione (GSH), carotenoids, α-Tocopherol, phenol, proline. These two arms scavenge ROS in a cooperative fashion. In this study, we pivot on Cd stress mediated ROS generation, ROS chemistry and localization and their scavenging mechanism resolved by both arms of the antioxidative defence systems, emphasizing their promising role in Cd stress tolerance. Such inclusive knowledge on antioxidant defence will permit us to evolve genetically engineered Cd stress-tolerant plants.