Mechanisms of Action of Nanoparticles in Living Systems

2. Ros And Antioxidant System In Plants

Reactive Oxygen Species (ROS) are unwelcome companions in entire aerobic life of an organism (Halliwell and Gutteridge, 1989). These partially reduced or activated derivatives of oxygen [singlet oxygen (¹O₂), superoxide anion (O₂^-), hydrogen peroxide (H₂O₂) and hydroxyl radical (HO^.)] are highly reactive and toxic, and can lead to the oxidative destruction of cell components (Asada and Takahashi, 1987). Evolution has conferred efficient mechanisms for scavenging ROS in all the aerobic organisms involving anti-oxidative enzymes and anti-oxidant secondary metabolites. The enzymatic scavenging system for ROS is composed of a battery of anioxidative enzymes such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), glutathione peroxidase (GPX) and glutathione-S-transferase (GST). This system is efficiently supported by non-enzymatic components like glutathione (reduced and oxidized forms), α-tocopherol and phenolic compounds (Gill and Tuteja, 2010). Plants control ROS effectively and use it beneficially as signaling molecule to control specialized processes such as plant growth, defense, hormonal signaling, and development (Ahmad et al., 2010).