Effect of the age of tobacco leaves on photosynthesis and photorespiration

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Relationships among the activities of enzymes related to photosynthesis and photorespiration, and ^<14>CO_2 photosynthetic products were investigated with individual tobacco leaves attached to the stalk from the bottom to the top. P-glycolate phosphatase of the chloroplasts and glycolate oxidase of the peroxisomes had their maximum activities in the 25th leaf from the dicotyledons. Maximum photorespiration was similarly distributed. The highest ratio of serine-^<14>C to glycine-^<14>C in the photosynthesates and maximum glycolate formation were also observed in the 25th leaf. Glutamate-glyoxylate aminotransferase, serine hydroxymethyltransferase and glycine decarboxylase were more active in the upper leaves. RuDP carboxylase had nearly constant activity In all leaves, except for the youngest in which activity decreased. Maximum CO_2 photosynthesis and enzyme activity for the C_4 dicarboxylic acid cycle occurred in the upper, youngest leaf. Distribution of photosynthetic CO_2 fixation among the leaves did not coincide with RuDP carboxylase activity. The photosynthetic capacity appeared to be better related to the distribution pattern for enzymes of the C_4 dicarboxylic acid pathway, i.e. PEP carboxylase, pyruvate Pi dikinase and 3-PGA phosphatase in the upper leaves. The results suggest that the C_4 dicarboxylic acid pathway participates, to some extent, in photosynthesis in young leaves of tobacco, a dicotyledonous plant.
日本植物生理学会の論文

Effect of the age of tobacco leaves on photosynthesis and photorespiration

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