C-14-STUDIES ON APPLE-TREES .9. SEASONAL-CHANGES IN THE FORMATION OF FRUIT CONSTITUENTS AND THEIR SUBSEQUENT CONVERSIONS

The formation and subsequent conversions of 14C‐labelled compounds were followed in fruits of Malus domestica cvs. Golden Delicious and Cox's Orange Pippin after labelling proximate leaves with 14CO2 at different times during the growing season. A few hours after labelling of the leaves, the larger share of fruit 14C was detected in sorbitol. This share descreased rapidly except in the late autumn. When labelling about 1 July (c. 1 month after bloom), 40–60% of the fruit 14C was permanently fixed in the methanol and water insoluble fraction. 25% or more was primarily found in organic acids, but this declined during the season to a few per cent. When labelling at the end of July, the dominating feature was the establishment of a peak of temporarily insoluble 14C, returning back to the soluble form through October and November. This was particularly pronounced in‘Cox's Organe Pippin'. Labelling with 14C at the end of August and at the end of September yielded increasing amounts of 14C in sugars. The labelling of fructose predominated, but as the autumn progressed the amount of label in sucrose increased. This was due to a conversion from 14C‐compounds of older origin as well as to a larger share of the imported assimilates turning into sucrose at this time of the year. During prolonged storage of harvested fruits at 3°C, 14C in fructose increased at the expense of 14C in sucrose. Copyright © 1979, Wiley Blackwell. All rights reserved