Dependence of Tuberization of Potato Stem Segments on Nucleic Acid and Protein Synthesis

Abstract

In the aseptic culture of the stem segments which were cut from the tuber-induced potato plants, these segments started outgrorth of lateral buds soon after inoculating to medium, and formation of tiny new tubers readily succeeded at the end of a certain linear growth period of the lateral shoots. A number of investigators have demonstrated an intimate relationship between nucleic acid metabolism and growth of plant. If the whole nucleic acid complement or some fraction of it in fact controls the initiation of potato tuberization, an inhibition of its synthesis should have some effects on the tuberization of potato. The present experiments were designed to answer the following question: does the tuberization on the aseptic culture of the potato stem segments depend specifically on the synthesis of new nucleic acids and protein ? When the stem segments were cultured on White's nutrient medium supplemented with 8 % of sucrose, an initiation of their tuberization was enhanced by advancing senescence of the mother tubers. Application of 2-thiouracil or 6-azauracil at the beginning of culture resulted to inhibit completely not only the linear growth but the tuberization of the lateral shoots grown from the stem segments. These inhibition could be more or less partially relieved with simultaneous addition of uracil, uridine or orotic acid, except for the case of orotic acid to the azauracil-induced inhibition. While a considerable attenuation of these inhibitory action became gradually to be apparent when the inhibitors were supplied at the advancing stage of culture, the suppression of the tuberization was still complete. On two days before starting the tuberization, no more significant effect on both the growth and tuberization was eventually observed due to the introduction of 6-azauracil. Repressing effect on the tuberization was also caused with chronic or brief treatment of ethionine and its inhibitory activity displayed a tendency to be intensified in proportion to the progressive development of the lateral shoot. Brief incubation with puromycin in the middle of culture period exerted a pronounced detrimental effect on the initiation of tuberization. On the other hand, 5-bromouracil and 6-azathymine produced no appreciable effect on it. In conclusion, the initiation of tuberization on the cultured potato stem segments is greatly accounted for on a basis of the specific RNA and protein which were synthesized in advance of the tuberization, while DNA shythesis did not participate in it. It can be deduced, therefore, that the induction of these synthesis is probably mediated through a certain suitable balance of endogenous growth substances contained in the stem segments.