Physiological and morphological studies on potato plants : Part 11. On the variation of ascorbic acid content of potato plants in irregular tuber formation.

Abstract

The present investigation is one of a series of experiments carried out under the title of physiological and morphological studies on potato plants. In the previous papers (1949, 1951), the authors have reported some assumptions concerning the mechanism of sprout tuber formation due to the senility of mother tubers. Judging from the results described in the above papers, it seems very reasonable to assume, therefore, that the irregular tuber formation of potato plants, such as sprout tuber, might be attributable to the changes of the reserve substances in the mother tuber and of the respiration rate of the sprout and tuber according to their storage conditions. In recent studies on the tuber formation of potato plants, the authors (1952) have made it obvious that the accumulation of ascorbic acid and the variations of carbohydrates contents in the potato tuber stand physiologically in a close interrelationship, namely, that the ascorbic acid may serve as an activator in the formation of starch in the potato tuber. The purpose of the present, investigation was chiefly to determine the relation between the variations of ascorbic acid and carbohydrate contents in the abnormal tuberization of potato plants under the various conditions, with a view to narrowing the problem whether the ascorbic acid may also act as an activator in the formation of starch in the abnormal tuberization of potatoes. The variety Irish Cobbler was used as material. The fractions analysed in the present experiments were similar to those described in the previous papers, so full descriptions are omitted here. The experimental results obtained may be summarized as follows ; (1) Under the storage conditions of dried and high temperature, the accumulation of starch and the rapid acceleration of growth in thickness of the sprout were recognized. With regard to the ascorbic acid content in the sprout tuber under these conditions, the content of oxidized form was much greater than that of the reduced form of ascorbic acid. The low content of the latter may be attributable to the oxidation of reduced ascorbic acid due to the high temperature condition. Accordingly, the accumulation of starch in the sprout tuber was less than that in the control tuber. (2) Being accompanied with the development of sprout tuber arose directly on the mother tuber, due to its senility resulting from long storage in a cellar. The accumulation of starch and the increase of ascorbic acid, especially of the reduced form, in the sprout tuber ran parallel. Accordingly the increase of the ratio of reduced from/oxidized form of ascorbic acid was one result. (3) When the seedlings of potatoes were placed in the dark, the ascorbic acid content in the tips of etiolated sprouts was much higher than the content in other parts of the sprouts. In the new tubers formed on the axils of the sprouts, however, the highest amounts of ascorbic acid and starch contents were recognized. (4) Judging from the results described above, if may be concluded that the localization of ascorbic acid in the tissue of potato plants tends to be parallel to that of the starch. Hence, in the case of the tuberization of potato plant, it seems very probable that the ascorbic acid, especially in the reduced form, plays an important role in the accumulation of starch and in the development of the tuber.