**6. Antioxidant enzymes**

The enzymatic and non-enzymatic mechanisms are available for scavenging of reactive oxygen species (ROS) in plants. The biochemical adaptive function of osmoprotectants to scavenge these harmful ROS by-products of hyperosmotic and ionic stresses causes membrane dysfunction and cell death ultimately. These active oxygen species are superoxide (O<sup>2</sup> −), hydrogen peroxide (H2 O2 ), hydroxyl radical (√OH), and singlet oxygen (1O<sup>2</sup> ) which is produced through oxidation phenomenon. Many plants have the ability to eliminate superoxide with the help of superoxide dismutase (SOD), which catalyzes the superoxide into H2 O2 and O2 . Thylakoid membrane has potential enzyme ascorbate peroxidase (APX) to eliminate hydrogen peroxide to save cell membrane from severe damage.

### **6.1. Superoxide dismutase**

SOD concentrations typically increase with the degree of stress conditions as the compartmentalization of different forms of SOD throughout the plant makes them counteract stress very effectively. There are three classes of SOD metallic coenzymes that exist in plants that act to control increased levels of oxidative stress. SOD's role as a free radical scavenger is established, and those genotypes have higher levels indicating a higher level of stress tolerance in wheat. The availability of different forms of SOD in plants show a maximum stress tolerance in affected crops, giving protection to the plant. The trends observed in the present research might be due to the reasons discussed earlier.
