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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.

Thiainn pyrophosphotransferase activity was present in seedling extracts from several monocot and dicot species of agronomic as well as nodcultivated plants. Changes in thiamin pyrophosphotransferase activity and thiamin pyrophosphate content were followed for 6 days in soybean (Menf.) Information on thiamin phosphorylation during the maturation and germination of seeds is insufficient and conflicting. TPP5 apparently is present in mature peanut seeds at a concentration of approximately 2% of total thiamin content (4). Conversely, Yusa (11) reported that phosphorylated forms of thiamin were absent from mature ungerminated seeds of corn, soybean, pea, and rice.The differences may stem in part from differential degradation of the phosphorylated derivatives of thiamin during seed maturation. Thiamin accumulates in maturing sunflower seeds, partially at the expense of TPP which is rapidly dephosphorylated during late maturation (2).Although unimbibed seeds of corn, soybean, pea, and rice apparently contained only thiamin, only phosphorylated forms were detected after seeds germinated (I1). In bean sprouts both thiamin synthetase and TPTase activities have been observed (7), and in 48-h pyruvate dehydrogenase complex from mitochondria of broccoli florets reversibly binds a metal-TPP complex (10). The steadystate reaction velocity of the pyruvate dehydrogenase complexmetal-TPP complex was reached only after a TPP-dependent lag phase and was related to the final concentration of metal-TPP. Hence, it was proposed that rapid dissociation of the metal-TPP complex from the enzyme might serve to regulate pyruvate dehydrogenase complex activity (10).The presence of antithiamin compounds in seeds, such as specific phenols, could attenuate the rate of seedling growth by lowering the availability of thiamin and TPP for necessary metabolic reactions (C. G. Wilkerson and R. C. Fites, unpublished data).TPP plays a crucial role in the energy and intermediary metabolism of living organisms, including seeds, by serving as a necessary coenzyme for &-keto acid dehydrogenases, transketolases, and decarboxylases (3). Thus, the enzyme(s) controlling TPP formation during seed germination and seedling establishment could conceivably coordinate the reactivation of essential metabolic pathways through the timely synthesis of TPP. Alternatively, sufficient TPP may remain associated with the apoenzymes requiring this coenzyme so that their reactivation occurs independent of any initial TPP formation. In this case, the increased activity of these pathways that occurs during rapid seedling growth would be dependent on an adequate provision of TPP.In soybean seedlings, only the latter alternative appears to apply. The data that support such a conclusion constitute the basis for this report.MATERIALS AND METHODS Seedling Growth. Except for tobacco, seedlings were grown as previously described (8)

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