Pyramiding of Two Antioxidant Enzymes CuZnSOD and cAPX from Salt Tolerant Cell Lines of Arachis hypogeae Confers Drought Stress Tolerance in Nicotiana tabacum

Antioxidant enzymes play an important role in conferring abiotic stress tolerance. The antioxidant metabolism protects cells from oxidative damage caused by ROS, such as peroxidation of membrane compounds, polysaccharide degradation, enzyme denaturation and DNA lesions Several enzymes act jointly to maintain redox status homeostasis. The antioxidative defense is initiated by SOD, which converts superoxide (O₂⁻) radicals to H₂O₂. The H₂O₂ that is also potentially harmful is converted to non-toxic water and monodehydroascorbate by the APX enzyme utilizing ascorbate as the electron donor. In the present study, genes for two different cytosolic antioxidant enzymes, superoxide dismutase (AhCuZnSOD) and ascorbate peroxidase (AhcAPX) isolated from salt tolerant cell lines of Arachishypogaea were simultaneously overexpressed in Nicotianatabacum to check the effect on alleviation of drought stress. Compared with untransformed control plants, transgenic plants survived under longer period of water deficiency and displayed improved recovery after rehydration. The enhanced levels of antioxidant enzymes in the transgenic plants correlated with higher relative water content, improved photosynthetic efficiency, elevated accumulation of compatible osmolytes, less malondialdehyde under stress conditions compared to untransformed controls. Our analysis showed that an increase in the activity of antioxidant enzymes can significantly enhance drought tolerance in transgenic plants, suggesting an important role of combined over expression of two antioxidant enzymes.