Activity of Glyceraldehyde-3-Phosphate Dehydrogenase-NADP in Developing Leaves of Light-Grown Dianthus chinensis L.

Quantitative histochemical methods were used to measure glyceraldehyde-3-phosphate dehydrogenase-NADP activity in developing and mature leaves of Dianthus chinensis L. The activity values were compared on the basis of illumination of developing leaves, the maturity of stomata, and the activity of enzymes concerned with carbohydrate oxidation. Activity on a kilogram dry weight per hour basis increased from the youngest primordia (50 mmol) to fully expanded leaves (1900 mmol) and then declined in older, senescing leaves. Enzymic activity increased from leaf base (400 mmol) to tip (1000 mmol) in leaf pair four, the tip of which was exposed to light, while activity of enzymes of carbohydrate oxidation decline. We propose that this leaf is beginning the transition to autotrophy, but does not fix significant amounts of atmospheric carbon because the stomata are not functional until leaf pair six.