Carbon Translocation in the Tomato: Pathways of Carbon Metabolism in the Fruit–

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Abstract
The rate of carbon import by tomato fruits has been related to their carbon metabolism by examining the effects of fruit temperature on the metabolism of imported assimilates. 14C–sucrose, –glucose, –fructose, –malic acid and –citric acid were injected individually into young growing tomato fruits which were subsequently maintained at 25 or 5 °C for 48 h. Fruit temperature greatly affected the proportions of 14C lost from the fruits by export and respiration. Only 40 per cent of the injected 14C from 14C–sugars and 20 per cent from 14C–acids was recovered from fruits at 25 °C. Less than 10 per cent of the injected 14C was exported, the balance being respired. In contrast, more than 50 per cent of the injected 14C was recovered from cooled fruits, in which the import rate of carbon was presumably reduced, and 20–36 per cent of injected 14C was exported. Cooling enhanced the synthesis of 14C–sucrose from injected 14C–hexoses and inhibited the incorporation of 14C into starch and insoluble residue. When 14C–sugars were injected, radioactivity exported from the cooled fruits was detected as sucrose in the phloem of the peduncles; radioactivity was also detected in stems and roots when fruits were cooled. In almost fully–grown fruits injected 14C–compounds were metabolized less readily than in smaller fruits. Conversion of 14C–hexoses to 14C–sucrose was again enhanced by cooling (5 °C, but was less in fruits maintained at 35 °C than in controls.