Soybeans [Glycine max(L.) Merr.] were harvested at various time periods after a 2‐h exposure to either 0 or 0.5 μ1/1 ozone to determine the effects of ozone on selected enzymes. Carbohydrate metabolism was modified by a depression of glyceraldehyde 3‐phaosphate dehydrogenase and an activation of glucose 6‐phosphate dehydrogenase. Ozone did not alter the levels of RNase, protease, acid phosphatase or esterase as might be expected if ozone enhanced leaf senescence. The activities of phenylalanine ammonia lyase, polyphenol oxidase and peroxidase were initially depressed and then stimulated following the ozone exposure. The reactions of soybeans to an acute ozone stress were more nearly akin to those elicited in response to other stresses than to the process of senescence.
Soybean [Glycine max (L.) Merr.] cultivars Dare and Hood were exposed to ozone (980 μg/m3) for 2 h to determine if differences in cultivar sensitivity were associated with differential activation of selected enzymes. The first trifoliate leaves of the cultivars were in similar stages of development (14 days from sowing) when exposed. The ozone treatment increased the activities of glucose 6‐phosphate dehydrogenase, phenylalanine ammonia lyase, polyphenol oxidase and peroxidase above the control in both cultivars within 30 h after exposure. However, the activity of all these enzymes increased several hours sooner in Dare (sensitive) than in Hood (tolerant). Our data suggest that the differential sensitivity of these two cultivars to ozone could be based on the differential ozone induced activation of the enzymes involved in the lesion formation process.
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