桑葉の生長にともなう炭酸固定及びグリコ-ル酸酸化酵素活性の変化

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Effect of the age of mulberry leaves on the rate of the photosynthetic oxygen evolution and the activities of RuDP carboxylase, 3-PGA phosphatase and glycoate oxidase were examined. The mature leaves showed higher rate of photosynthetic oxygen evolution, and higher activities of RuDP carboxylase and glycolate oxidase than those of the young leaves. Reversely, 3-PGA phosphatase activity was higher in the young leaves. Products of photosynthesis in 14CO2 for short time of period in the mature leaves were mainly alanine, glyceric acid, sugars, glycine and serine. In addition to these 14C photosynthates, in the young leaves 3-PGA was found as the most heavily labeled compound. Intramolecular distribution of 14C in serine found in both of the leaves showed nearly uniform distribution of 14C at each carbon atom. Formation of uniformly labeled serine during short exposure to 14CO2 suggests the rapid flow of carbon through the glycolate pathway. The carboxyl carbon of alanine was more heavily labeled than other two carbon atoms in both of the laves and its degree was higher in the young leaves than that of the mature leaves. These may suggest that alanine formed during photosynthesis comes mainly from 3-PGA and the contribution of 3-PGA formed as the product of RuDP carboxylase to alanine synthesis is larger in the young leaves.
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