The Distribution of45Ca in Apple Fruits when Supplied to the Roots at Three Times During the Season

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Abstract
During the first four or five weeks of fruitlet development, root-absorbed 45 Ca entered the vascular bundles throughout the whole fruit. Subsequently, no uptake could be detected in the outer cortex. When the fruitlets were about six weeks old, 45 Ca applied to the roots two weeks before had diffused through the cells, including the pith, although radioactivity in the vascular bundles associated with the carpels, sepals and petals remained high at this time. There was very little uptake by the fruits of 45 Ca supplied in early August: autoradiographs prepared four weeks later showed activity to be mainly in the fruit stalk, whilst in the fruit, trace amounts were found in the cartilaginous pericarp and ventral carpellary bundles. It is suggested that part of the calcium requirement moves into the fruit skin from the epidermis of the fruit stalk as well as through the vascular system. The significance of the changing pattern in distribution of 45 Ca is discussed in relation to other changes in the fruit during development, e.g. transpiration, and to the environment. The commercial use of foliar applications of Ca salts to raise fruit Ca levels is also discussed.