Abstract:

Changes in fruit color, anthocyanins and phenolic compounds concentrations and the relative expression of
MdMYB1, MdbHLH3, MdbHLH33, MdTTG1, MdCHS, MdDFR, MdANS and MdUFGT were determined in apple skin of
bagged and bag-removed ‘Granny Smith’ fruits. Light is a key factor for fruit coloration. Red color development, flavonol
accumulation and anthocyanin biosynthesis in apple fruit skin were depressed by fruit bagging, while the values of L* and
b* dropped, a* value and the concentrations of cyaniding-3-galactose, quercetin-3-galactoside and quercetin-3-rhamnosyl
glucoside were increased radically in apple skin of ‘Granny Smith’ after bag removal, indicating the deepening of red color
in the skin; fruit debagging had no significant effects on chlorogenic acid, phlorizin and procyanidine accumulation. Similar
to anthocyanins, transcript levels of MdMYB1, MdbHLH3, MdbHLH33, MdTTG1, MdCHS, MdDFR, MdANS and MdUFGT,
the genes involved in anthocyanin biosynthesis were also depressed by fruit bagging. All the genes were induced by light
after bag removal. It is demonstrated that fruit bagging inhibits anthocyanin biosynthesis by supressing the expression of
genes involved in anthocyanin biosynthesis, and these genes could be induced by bag removal, leading to anthocyanin
accumulation in apple skin.

Key words: Granny Smith, anthocyanin, polyphenol, gene expression, bagging