14C-Studies on Apple Trees III. The Influence of Season on Storage and Mobilization of Labelled Compounds

The present paper reports an attempt to elucidate the storage and mobilization processes in 1-year-old apple rootstocks by studying the ¹⁴C content of different parts of the tree following application of ¹⁴CO₂. The translocation of the ¹⁴C taken up from the leaves to other parts proceeds at the highest rate during the first few days after the application of ¹⁴C. The distribution in shoots, trunk and roots after application of ¹⁴C during May, July, August, and in part of September depends in particular upon the intensity of growth in the various parts. From the lime of the application of ¹⁴C until leaf-fall, 40–50 per cent of the ¹⁴C initially absorbed disappears from the tree. After exposure to ¹⁴C during October, and in part of September, a relatively large part of the ¹⁴C applied goes to the root. In this case there is a considerable reduction in the ¹⁴C-conlent from leaf-fall to the following spring after leafing, especially in the root, although relatively speaking reduction is also considerable in the bark of the parts above ground, and it is most pronounced in the methanol (80 %) soluble fraction. The reduction takes place primarily during spring, and comprises, after application during October, for the whole tree 20–25 per cent of the ¹⁴C initially absorbed. Only 13–17 per cent of this amount was recovered in the newly developed shoots and leaves in the following June.