In many ornamental plants, anthocyanin accumulation in leaves is a critical determinant of foliage coloration. However, the mechanism by which photoperiod and shading affect coloration and anthocyanin accumulation in the leaves of woody plants is less clear. By examining the leaves and calli of crabapple (Malus spp.) cultivars with different leaf color characteristics, we analyzed the foliage coloration, flavonoid contents, and expression levels of anthocyanin biosynthetic genes and the McMYB10 transcription factor under different photoperiods and shading treatments. The red color parameters, flavonoid contents, and expression levels of some anthocyaninrelated genes in both the leaf and callus were generally higher under sun-exposure or long-day treatments compared to shading or short-day treatments. These data indicate that red color formation in cultivars with leaves that are naturally red requires a suitable photoperiod and light intensity; high light intensity or long-day conditions activate anthocyanin biosynthesis-related genes, leading to anthocyanin accumulation. Our results also indicate that the regulation of anthocyanin biosynthetic metabolism in response to light conditions differs between red-leafed and green-leafed cultivars. Taken together, our data reveal that photoperiod and light intensity are important in the regulation of pigmentation and anthocyanin accumulation in crabapple leaves and calli. Moreover, we provide a useful approach for studying and inducing the production of flavonoids by crabapple callus culture under certain photoperiods.

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