Light versus Dark Carbon Metabolism in Cherry Tomato Fruits: I. Occurrence of Photosynthesis. Study of the Intermediates.
The photosynthetic properties of the internal and peripheral tissues of the cherry tomato fruit (Lycopersicum esculentum var. cerasiforme Dun A. Gray) were investigated. Whole fruit and their isolated tissues evolve large amounts of CO(2) in darkness. In the light, this evolution decreases but nevertheless remains a net evolution; 3-(3,4-dichlorophenyl)-1,1-dimethylurea abolishes the effects of light.Incorporation of (14)CO(2) by leaves and fruit tissues demonstrates that the outer region of the fruit has the highest photosynthetic efficiency on a chlorophyll basis; the internal fruit tissue, richer in chlorophyll, has a much lower efficiency. The identification of intermediates following short term incubations with (14)CO(2) shows that in darkness the fruit accumulates the majority of label in malate. In the light, leaf tissue exhibits a pattern of incorporation characteristic of C-3 metabolism, whereas fruit tissue exhibits a decreased labeling of malate with a concomitant appearance of label in Calvin cycle intermediates. This is in agreement with the levels and types of carboxylating activities demonstrated in vitro; especially noteworthy is the very low ribulose diphosphate carboxylase activity in the internal fruit tissue.The photosynthetic potential, phosphoenolpyruvate carboxylase activity, and quantities of malate accumulated by fruit tissues are parallel to their chlorophyll content during growth and maturation.
Laval-Martin
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Laboratoire de Cytophysiologie de la Photosynthèse, C.N.R.S., 91190 Gif-sur-Yvette, France.