Photosynthetic & respiratory activities of growing pea leaves

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Abstract
Manometric measurements of the photosynthesis and respiration of pea leaves (Pisum sativum variety Laxton''s Progress) were made at different stages of leaf growth. Photosynthesis per unit fresh weight of leaf or per single leaf at first increased and reached a maximum before the leaves were fully expanded. The rate of photosynthesis then slowly fell. Respiration per unit fresh weight of leaf decreased continuously during leaf maturation. The following enzymes were assayed at various times during leaf growth ribulose 1,5-diphosphate carboxyl-ase, photosynthetic pyridine nucleotide reductase, enolase, 6-phos-phogluconic acid dehydrogenase, aconitase and transketolase. Changes in the activities of the 1st 2 enzymes during leaf growth paralleled that of photosynthesis. In contrast, enolase, 6-phosphogluconic dehydrogenase and aconitase showed changes during leaf growth approximating that of respiration. The variation in transketolase activity during leaf growth was intermediate between the changes in the photosynthetic and respiratory rates. The significance of these results in relation to the physiological development of leaves is discussed.