Conversion of C-Labeled Acetate to Citric and Malic Acids in the Tomato Fruit.

The possible intermediary position of the plant acids in respiration and carbohydrate metabolism as indicated for some plant tissues, suggests that a similar situation may exist in fruit. Many fruits contain comparatively large amounts of various acids (8) and apparently have a very active acid metabolism, as shown by the changes in concentration which occur during growth, ripening and storage. TURNER (10), for example, found that most of the citric acid in apple tissue was actively engaged in the metabolic flux during the post-harvest cold storage period. He concluded that the data of his experiments are compatible with the participation of a Krebs cycle in carbohydrate oxidation in the apple, but do not prove that such a cycle exists. While C14-labeled substrates have been used extensively for studying intermediary metabolism in some plant tissues, their use in connection with fruit has not been reported, so far as known. In preliminary experiments with tomato fruit, it was found that following injection with C14-labeled sodium acetate, radioactivity appeared in the respiratory C02, the acids, and in certain other fractions isolated from the juice and tissue. Data from degradation studies on citric and malic acid which suggest the participation of a Krebs cycle in tomato fruit metabolism are presented.