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Light versus Dark Carbon Metabolism in Cherry Tomato Fruits

II. Relationship Between Malate Metabolism and Photosynthetic Activity

Danielle Laval-Martin²

¹ Commissariat à l'Energie Atomique, Département de Biologie, B.P. No. 2, 91190 Gif-sur-Yvette, France, Laboratoire de Cytophysiologie de la Photosynthèse, C.N.R.S., 91190 Gif-sur Yvette, France

The possible relationship between malate metabolism and photosynthetic activity in green tomato fruit tissues (Lycopersicum esculentum var. cerasiforme Dun A. Gray) was investigated. Initial experiments consisted of vacuum-infiltrating ¹⁴C-3 or ¹⁴C-4-malate into isolated tissues in darkness and then incubating the tissues under photosynthetic conditions. Other experiments involved a short pulse with ¹⁴C-bicarbonate in darkness to label the malate pool(s), followed by a chase in the light in the presence of nonradioactive bicarbonate. Both series of experiments were followed by the separation and identification of labeled metabolic intermediates.

Label initially in carbon atoms 3 and 4 of malate, corresponding also to C-3 of pyruvate and CO₂ after malate decarboxylation, was recovered as citrate + isocitrate, sugars and starch following incubations of tissues in the light. These data demonstrate that the reductive pentose phosphate cycle utilizes CO₂ furnished by malate metabolism due to the operation of the citric acid cycle and perhaps also to malic enzyme activity. Some synthesis of sugars and starch from C-3 of malate was observed in darkness or in the light 3-(3,4-dichlorophenyl)-1,1-dimethyl which could be due to gluconeogenesis. Pulse-chase experiments indicated a rapidly turning over malate pool.

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