Developmental Changes in Enzymes of Flavonoid Biosynthesis in the Skins of Red and Green Apple Cultivars

Abstract

Three enzymes of flavonoid biosynthesis (phenylalanine ammonia-lyase (PAL), chalcone isomerase (CHI) and glycosyltransferase (UFGT)) were assayed during the development of apple (Malus pumila Mill) fruit. Total flavonoid and anthocyanin concentrations were measured (by HPLC) during the same period. The same patterns of change in activity were observed with all three enzymes in both a red (‘Splendour’) and a green-skinned cultivar (‘Granny Smith’). Enzyme activities were high in the immature fruit, decreased during the middle of the season and rose on ripening, activity in ripe fruit was generally not as high as in immature fruit. Total flavonoid concentration correlated with the activity of CHI and UFGT throughout development. In ‘Granny Smith’ there was correlation between flavonoid concentration and PAL but not in ‘Splendour’ except during ripening, when the fruit reddened. In ‘Splendour’ the activity of all three flavonoid enzymes correlated with anthocyanin levels during reddening. At all stages enzyme activity in ‘Splendour’ was several-fold higher than ‘Granny Smith’; daily rates of synthesis of the flavonoids were also much higher.