Concentration of dehydroasco_??_bic acid in lettuce

(1) The present experiment was undertaken to prove the amount of dehydroascorbic acid, effect of photosynthetic activities on the formation of ascorbic acid, and activity of enzymes which oxidizes ascorbic acid into dehydroascorbic acid in lettuce plants. (2) Five varieties used for experiments were New York, Imperial, May King, Wayahead, and Oak-leafed. The plants were grown under field conditions, and the samples were collected at certain definite periods. (3) The amounts of dehydroascorbic acid and ascorbic acid in the lettuce plants were determined by the titration method with 2.6-dichlorphenol-indophenol solutions, described by FUJITA et al. (4) A considerable amount of dehydroascorbic acid was detected in the fresh blades which were just being cut. (5) The formation of total ascorbic acid in leaves of lettuce is affected by the photosyn-thetic activities, but no remarkable effect on the ratio of ascorbic acid and dehydroascorbic acid. (6) It is shown by means of a ascorbic acid oxydase test that the ascorbic acid oxydase might be absent in the extracted juice, because no reaction of enzyme appeared on synthetic ascorbic acid solutions after adding the juice to it. (Laboratory of Agronomy, Faculty of Agriculture, Tokyo University, Hongo, Tokyo, Japan.)