THE EFFECT OF SALT STRESS ON THE ANTIOXIDANT DEFENSE MECHANISMS OF TWO WHEAT (Triticum aestivum L.) CULTIVARS

In order to overcome environmental stresses that diminish the performance of such crops as wheat, it is necessary to realize intra-cellular circumstances. For this purpose, two cultivars of wheat (Triticum aestivum L.), namely 'Kohdasht' and 'Gaskogen' were treated at 3 to 4- leaves stage by 200 mM sodium chloride (NaCl) for 14 days. The enzymic activities of catalase (CAT), ascorbate peroxidase (APX) and glutathione S-transferase (GST) in the case of 'Kohdasht' significantly decreased compared to the control as a result of salinity. The activity level of guaiacol peroxidase (GPX), however, did not show a significant change. The enzymic activity of GPX and GST, also, in the case of 'Gaskogen' showed a significant increase compared to the control while APX and CAT did not have any significant variation. It is argued that the sum of activities of hydrogen peroxide (H2O2)-scavenging enzymes helped control the amount of the pernicious compound (H2O2) in 'Gaskogen'. The reverse results were obtained in terms of 'Kohdasht'. On the other hand, salt stress led to the significant increase of malondialdehyde (MDA) in both wheat cultivars, although membrane damage and lipid peroxidation were more severe with regard to 'Kohdasht'. It follows that the augmentation of H2O2 and the drop in GST activity substantiates further increase in the amount of MDA in 'Kohdasht'. It is concluded that the activity of H2O2 scavenging enzymes and that of GST enzyme has a crucial role in detoxifying toxic compounds leading to more resistance against salt stress.