Translocation of 14C-Photosynthates in Isolated Sweet Potato Leaves, Ipomoea batatas Poiret

摘要

There are many papers that the translocation is controlled to an appreciable extent by the mutual interaction among systems, i.e., source, conducting, and, sinks, then, it is presumed that each system is influenced by the other systems through the translocation. But, these interactions have been very slightly studied from the quantitative angle. Isolated sweet potato leaves have the advantage that photosynthates are translocated to the principal sinks, i.e., tuberous roots. Using the simplified system described above, the dry matter production and the translocation of 14C-photosynthates have been investigated. The results obtained were summarized as follows: 1. The leaf area of the isolated leaves increased in the early vegetation period, and did not wither during the period of 10 weeks. In spite of extensive leaf area, its photosynthetic rate continued to be relatively highter than that of the intact plants during the same period. The starch contents in the leaves did not increase with growing, being higher those in the intact plants. However, the former seemed not to differ greatly from the latter in contents of N, P, and, K in leaves. 2. The formation of tuberous roots was observed even in the isolated sweet potato leaves. From the standpoints of varietal characteristics, the isolated plants showed to be similar to the intact ones in enlargement of tuberous roots. No distinct differences were found between the isolated and the intact plants about the starch contents and the dry matter distribution ratios in the tuberous roots. 3. The amounts of 14C-photosynthates in the leaves, after exposure to 14CO2 for 1 hour, remarkably decreased during the subsequent period of 24 hours, and then decreased slightly during the period from 24 hours to 5 weeks. About 20% of 14C-photosynthates were assumed to move from the leaves to others within 30 minutes after exposure to 14CO2. 4. The specific activities of 14C-photosynthates in the tuberous roots increased at higher rate than those of the other organs with passage of time up to 24 hours after the treatment. 14C-photosynthates were primarily translocated towards the tuberous roots in a short time. 5. The specific activities of 14C-photosynthates in the stems·axillary buds were observed to be high throughout the experimental period. The translocation to the stems·axillary buds continued for long time under the conditions mentioned above. 6. More than 50% of 14C-photosynthates were disappeared from the plant during the period of 24 hours after exposure to 14CO2, possibly due to respiratory consumption. 7. From the autoradiographic observation, it was assumed that the translocation to the tuberous roots was directly related with the development of vascular bundles and the diffusion from them into the storage parenchyma.