Abstract: Anthocyanin content and activities of related enzymeswere measured in‘Ralls’and its budmutation. Effect of bagging on anthocyanin biosynthesis in bud mutation was also studied. The results showed: ①Anthocyanin content in mature fruits was 132170 U·g^-1FW in bud mutation which was very significantly higher than that in‘Ralls’(49140 U·g^-1FW) ; ②Activities of PAL and UFGT were almost the same between the two materials, but CH I and DFR activitieswere significantly high in bud mutation, which were related to the increase of anthocyanin levels in the mutant; ③Bagging treatment inhibited anthocyanin synthesis of bud mutation. But anthocyanin content had significantly increased after removing the bags. Activities of CHI and UFGT increased rap idly and were much higher than those in the control after the bag removal. The increase was consistentwith the imp rovement of anthocyanin levels. Above all, the key index of colouration mechanism of‘Ralls’and bud mutation is anthocyanin content and CHI activity.

Key words: apple, bud mutation, coloring mechanism, bagging