Springer Online Journal Archives 1860-2000
Abstract The current study confirmed earlier conclusions regarding differential ozone (O3) tolerances of two soybean cultivars, Essex and Forrest, and evaluated antioxidant enzyme activities of these two varieties based on their performance under environmentally relevant, elevated O3 conditions. The experiment was conducted in open-top chambers in the field during the 1994 and 1995 growing seasons. Exposure of plants to moderately high O3 levels (62.9 nl l−1 air, 2-year seasonal average) caused chlorophyll loss and increased membrane permeability when compared to control plants grown in charcoal filtered air (24.2 nl l−1 air). The other effects of O3 treatment were decrease in seed yield, loss of total sulfhydryl groups, reduction of soluble protein content, and increase in guaiacol peroxidase activity in leaves of both cultivars. The O3-induced increase in guaiacol peroxidase activity was much smaller in cv. Essex leaflets. Cv. Essex had less leaf oxidative damage and smaller reduction in seed yield than cv. Forrest under elevated O3 conditions. During ozonation, mature leaflets of the more O3 tolerant cv. Essex had higher levels of glutathione reductase (30%), ascorbate peroxidase (13%), and superoxide dismutase (45%) activity than did mature leaflets of cv. Forrest. Cu,Zn-superoxide dismutase, which represented 95% of total superoxide dismutase activity in the two cultivars, appeared to be increased by O3 exposure in the leaflets of O3 tolerant cv. Essex but not in those of cv. Forrest. Cytosolic ascorbate peroxidase activity was also higher in leaflets of cv. Essex than in cv. Forrest regardless of O3 level. Stromal ascorbate peroxidase and Mn-superoxide dismutase activity did not appear to be involved in the O3 tolerance of the two soybean cultivars.
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