Flavonoid biosynthesis and accumulation and related enzyme activities in the skin of 'Fuji' and 'Oorin' apples during their development

Abstract

To ascertain the mechanism of apple skin coloration, changes in the flavonoid biosynthesis and accumulations and related enzyme activities were investigated during fruit development in red-skinned 'Fuji' and green-skinned 'Oorin' apples. In 'Fuji' anthocyanin accumulated from 139 days after full bloom (DFB) concurrent with fruit maturation. Proanthocyanidins and flavonols showed highest concentrations in very young fruit; then decreased gradually afterwards and remained almost constant throughout fruit development in both cultivars. Changes in phenylalanine ammonia-lyase (PAL) activity corresponded withthese patterns, but they slightly increased in 'Fuji' 139 DFB. The changing pattern of chalcone isomerase (CHI) activity was similar to that of PAL until maturation when a slight increase in CHI activity was observed. CHI activity in 'Fuji'apple skin was higher than that of 'Oorin'. In the 'Fuji' apple skin, UDP-3-O-glycosyltransferase (UFGalT) activity markedly increased from 139 DFB, parallel with anthocyanin accumulation. Our results suggest that anthocyanin synthesis mainly occurs during coloration in'Fuji'. PAL, CHI, and UFGalT enzymes are involved with antocyanin synthesis; UFGalT seems to be the most important enzyme in red pigmentation of 'Fuji'.