Ozone tolerance and antioxidant enzyme activity in soybean cultivars

The current study confirmed earlier conclusions regarding differential ozon e (O-3) tolerances of two soybean cultivars, Essex and Forrest, and evaluat ed antioxidant enzyme activities of these two varieties based on their perf ormance under environmentally relevant, elevated O-3 conditions. The experi ment was conducted in open-top chambers in the field during the 1994 and 19 95 growing seasons. Exposure of plants to moderately high O-3 levels (62.9 nl l(-1) air, 2-year seasonal average) caused chlorophyll loss and increase d membrane permeability when compared to control plants grown in charcoal f iltered air (24.2 nl l(-1) air). The other effects of O-3 treatment were de crease 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 O-3-induced increase in guaiacol peroxidase activity w as much smaller in cv. Essex leaflets. Cv. Essex had less leaf oxidative da mage and smaller reduction in seed yield than cv. Forrest under elevated O- 3 conditions. During ozonation, mature leaflets of the more O-3 tolerant cv . Essex had higher levels of glutathione reductase (30%), ascorbate peroxid ase (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 increas ed by O-3 exposure in the leaflets of O-3 tolerant cv. Essex but not in tho se of cv. Forrest. Cytosolic ascorbate peroxidase activity was also higher in leaflets of cv. Essex than in cv. Forrest regardless of O-3 level. Strom al ascorbate peroxidase and Mn-superoxide dismutase activity did not appear to be involved in the O-3 tolerance of the two soybean cultivars.