Awad et al. (2000) suggested that very low levels of anthocyanins, moderate levels of quercetin 3-glycosides and relatively high levels of phloridzin, catechins and chlorogenic acid, are found in the shaded skin of an individual fruit and also in
the skin of a fruit borne inside the canopy, indicating that anthocyanin synthesis is a light-dependent process, while the synthesis of other phenolic metabolites is only slightly, if at all,light-dependent. Ju (1998) found that the genes controlling the synthesis of different phenolic compounds might have a different sensitivity to light. Since accumulation of quercetin glycosides and cyanidin 3-galactoside has no influence on accumulation of any of the other flavonoid classes, their biosynthesis seems to be
regulated independently of the other classes, although they have the same biosynthetic pathway (Awad et al., 2001a).