DIFFERENTIAL RESPONSES OF TWO WHEAT VARIETIES TO INCREASING BORON TOXICITY. CHANGES ON ANTIOXIDANT ACTIVITY, OXIDATIVE DAMAGE AND DNA PROFILE

The present study comparatively analysed divergences in root and coleoptile growth, the modulation of enzymatic antioxidant system, production of reactive oxygen species (ROS) and the extent of oxidative damage (membranes and DNA structure) in a drought-tolerant (cv. Bezostaya) and drought-sensitive (cv. Alpu) cultivars of wheat under 4, 5, and 6 mM boron concentrations. Reduction in root and coleoptile growth was greater in Alpu than in Bezostaya. Although soluble protein content increased in both cultivars compared to their controls, increase in the Bezostaya was higher than in Alpu. Contents of ROS superoxide anion (O-2) and hydrogen peroxide (H2O2) increased significantly in root and coleoptiles of both varieties, and the increase in Alpu was very high compared to Bezostaya. Bezostaya had higher superoxide dismutase (SOD) activity than Alpu. In contrast to high SOD activity, H2O2 content was lower in Bezostaya than in Alpu. While H2O2-scavenging enzymes guaiacol peroxidase (GPX) and ascorbate peroxidase (APX) activities increased in Bezostaya, activity of APX alone increased in Alpu. Catalase (CAT) activity decreased in both varieties. Besides, DNA and membrane damages were lower in Bezostaya than in Alpu. These results suggested that Bezostaya showed a better protection mechanism against oxidative damage caused by boron toxicity by its higher induced activities of antioxidant enzymes and more effective osmotic modulation than in Alpu.