DISTRIBUTION OF SUGARS AND RELATED ENZYMES IN THE STEM AND BLOSSOM HALVES OF VALENCIA ORANGES

The distribution of sugars (sucrose, glucose, and fructose) and relate d enzymes between the stem and the blossom halves of 'Valencia' orange s [Citrus sinensis (L.) Osbeck] was determined at three stages of frui t development. The blossom half contained significantly higher concent rations of sugars during later stages of development and maturation (1 2% and 20%,respectively). Neither the enzyme marker for sucrose synthe sis [sucrose-phosphate synthase (SPS)] nor enzymes of CO2 fixation (NA DP-malic enzyme, PEP carboxylase, and PEP carboxykinase) were signific antly different between the halves. Sucrose synthase (SS), the enzymat ic marker for sink strength, had significantly higher activity in the blossom half during later stages of fruit development when rapid sugar accumulation takes place. These data suggest that differential distri bution of sugars between the stem and the blossom halves of citrus fru it is, in part, the result of differential sink strength.