Effect of Water Stress on Antioxidant Enzymes Activities and Lipid Peroxidation of Wheat Seedlings

Considering the role of wheat in food security of Iran and its yield reduction due to drought stress، three varieties of wheat، Azar2، Alvand and Zarin were selected and cultured under hydroponics condition. At the fourth to fifth leaf stage the seedlings were kept under 4، 8 and 12 bars potential using polyethylene glycol 8000 (PEG 8000). Hogland solution was used as the control. After 10 days، leaf samples from the seedlings were obtained and antioxidant enzymes activity (Superoxide dismutase (SOD)، Catalase (CAT)، Ascorbat peroxidase (APX) and Glutathion reductase (GR)) and lipid peroxidation were evaluated. Results showed that increase in the strength of osmotic stress increased lipid peroxidation. Moreover، the activity of SOD was declined in the varieties، but GR activity was enhanced with the increase of osmotic stress as expected. This enzyme was not the restriction factor of wheat defence mechanism activities against the environmental stresses. At 12 bars، the activity of APX in Alvand and Azar2 cultivars، contrary to Zarin، showed a significant increase (P<5%) as compared with the control. Nevertheless، the CAT activity was equal in all levels in Azar2، increased in Zarin and declined in Alvand. Subsidence of the enzyme activity of SOD، CAT and APX in Alvand and Zarin cultivars resulted in lower yield due to loss of balance among the elements of defense mechanisms. Thus with accumulation of reactive oxygen species، the key points of the metabolism and cell defence mechanisms were damaged. These factors resulted in the sensitivity of varieties to osmotic stress in contrary to Azar2.