Mid-season movement of ⁴⁵Ca in apple trees

Abstract

Apple trees (cv. Granny Smith) were grown in sand or water cultures supplied with a complete nutrient solution. ⁴⁵Ca added to this solution c. 11–14 weeks after full bloom became distributed throughout each tree. It moved preferentially into the interveinal tissues of the young rather than the old leaves of the terminal growth. The ⁴⁵Ca concentration was highest in the petiole, midrib, and veins and comparable for both types of leaf in these tissues. In the tree trunk, leaders, and fruit spurs the ⁴⁵Ca concentration was much higher in the bark than in the wood. Although the isotope entered the bark and leaves of the fruit spurs it was not detected in the flesh of the attached fruits. It occurred in low concentration in the pedicels of a few fruits.

When supplied to trees 4–5 weeks after full bloom, ⁴⁵Ca did enter the fruits, but its concentration was much less than in the bark of the fruit spurs. In such fruit the concentration of ⁴⁵Ca was highest in the core towards the stem end, least in the flesh, and intermediate in the peel.