Pantothenic Acid and Acetic Acid Utilization in Tomato Fruit-set.

Fruit-set in the tomato has been shown to be dependent upon the presence of mature leaves (3). The nature of the nutritive materials supplied by the leaves has been studied by use of excised tomato flowers cultured on an agar medium to which various nutrients have been added. Of the organic acids tested, all those participating in the Krebs tricarboxylic acid cycle were found to be effective in sustaining fruit-set, but several acids not in the Krebs cycle were essentially ineffective in fruit-set. One of these ineffective acids was acetic acid. It has been demonstrated that coenzyme A, which contains pantothenic acid as a functional group (5, 6) is required for the utilization and metabolism of acetate (4, 5, 7, 8, 9). The present report demonstrates that if pantothenic acid is supplied to excised tomato flowers, they are capable of utilizing acetic acid as effectively as acids of the Krebs cycle in fruit-set. The methods and materials used in these experiments are identical with those reported in the previous study (2). Unset flowers of a self-sterile strain of John Baer tomato were excised, sprayed with auxin, and subsequently grown on agar culture media to which the nutrients being tested had been added. The flowers which had set fruit were recorded after 8 days. At least 15 flowers were used for each value reported. If excised flowers are sprayed with auxin (30 mg./l. p-chlorophenoxyacetic acid) and placed on an agar medium containing only acetic acid, very little fruit-set is obtained over a wide concentration range. Such a response is seen in the "control" curve of figure 1. If, however, pantothenic acid (10 mg./l.) is included in each dish, a striking quantitative response to acetic acid is obtained (fig. 1) reaching 607% fruit-set at 10-3 M acetic acid. The effectiveness of pantothenic acid in facilitating the acetate utilization is quantitative over a concentration range of 0.01 to 10 mg./l. of pantothenic acid, the last concentration producing the greatest effect. If the pantothenic acid is facilitating the conversion of acetate to citrate via the reaction catalyzed by coenzyme A, one would expect the effect to be blocked by fluoroacetate. Inclusion of sodium fluoroacetate (10 M) in each dish with the pantothenic acid did in fact effectively inhibit fruit-set at each level of acetic acid (fig. 1). If the pantothenic acid is actually facilitating the utilization of acetate, the effect should be specific for that acid. Testing several different organic