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Plants exposed to stress undergo changes in their metabolism in order to adapt to the changes in their environment. The present study deals with the effect of abscisic acid (ABA), poly ethylene glycol (PEG) mediated water stress and NaCl stress on superoxide dismutase (SOD) activity in leaves of Withania somnifera (L.) Dunal. Leaves of W. somnifera were incubated in vitro with different concentrations of ABA, NaCl and PEG with duration ranging from 0 to 8 hours. Both ABA and NaCl had a significant effect on the enzyme activity with maximum activity occurring during 4th and 6th hour in both stresses. However, the PEG mediated drought stress revealed no significant change in the SOD activity. The results in the present study highlights a probable occurrence of oxidative burst in Withania leaves during 4th and 6th hour of stress signaling.
Exposure of plants to unfavorable environmental conditions such as vicissitudes of temperature, high light intensity, water availability, air pollutants or salt stress can increase the production of reactive oxygen species including hydrogen peroxide (H2O2), hypochlorous acid (HClO), and free radicals such as the hydroxyl radical (OH_) alkoxyl radical (R), singlet oxygen (1O2) and the superoxide anion (O2 - ) (Apel and Hirt, 2004). These oxidants can damage cells by chemical chain reactions like lipid peroxidation, or by oxidizing DNA and proteins (Alscher et al., 2002; and Pastori and Foyer, 2002). Hence, plants maintain complex systems of multiple types of antioxidant enzymes such as superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR) and glutathione-synthesizing enzymes to contain the damage caused by Reactive Oxygen Species (ROS) (Sairam and Tyagi, 2004; and Wolf, 2005).
Superoxide radical is regularly synthesized in the chloroplast (Elstner, 1991) and mitochondria (Rich and Bonner, 1978), though some quantity is also reported to be produced in microbodies (Lindquist et al., 1991). Superoxide Dismutases (SODs, EC 1.15.1.1) are ubiquitously expressed antioxidants enzyme in aerobic organisms and catalyze dismutation of superoxide anion to hydrogen peroxide and molecular oxygen and is the first line active oxygen scavenging system. Scavenging of O2 - by SOD results in the production of H2O2, which is removed by APX (Asada, 1992) or catalase (Scandalias, 1990). |
