14C‐Studies on Apple Trees. I. The Effect of the Fruit on the Translocation and Distribution of Photosynthates

The presence of fruits affects the translocation and distribution of photosynthates from apple leaves to other organs of the tree. An attempt has been made to study the relationship in greater detail by following the distribution of 14C introduced in the form of 14CO2 on shoots with and without fruits, respectively. Determinations of the 14C-content were made on different parts of the shoot sampled at varying intervals after the introduction of the tracer. The l4C-labelling and the content of sorbitol and sugar in the leaves were determined by means of paper chromatography. A total of nearly 90 per cent of the 14C taken up by the leaves can be transferred to a fruit close by, the majority during the first 4 to 5 days following the addition of the 14C. The content of 14C in the leaves is reduced more rapidly in shoots with fruits than in those without. Young leaves retain more of the added 14C than do fully developed ones. The greatest changes with time are found in the methanol-soluble 14C-compounds. Immediately following application, the leaves contain 58 to 80 per cent of the 14C added in sorbitol, 7 to 9 per cent in sucrose, and 1 to 4 per cent in the form of glucose. Within 5 days after the introduction of 14C the amount of 14C-sorbitol is reduced very considerably, while in certain cases the amount of 14C-glucose increases. The 14C-sorbitol content was higher in leaves from shoots without fruits than in those from fruit-bearing shoots, and this applied also to the total contents of sorbitol and of glucose.