Flavonoid content and expression analysis of flavonoid biosynthetic genes in herbaceous peony (Paeonia lactiflora Pall.) with double colors

Herbaceous peony (Paeonia lactiflora Pall.) is a famous flower with medicinal values, and its flowers have a number of medicinal constituents, especially flavonoids. In this study, a P. lactiflora cultivar with double colors including white outer-petal and yellow inner-petal was used as the experimental materials to perform the qualitative and quantitative analysis of flavonoids by high-performance liquid chromatograph-electrospray ionization-mass spectrometry (HPLC-ESI-MSn) and investigate the expression patterns of flavonoid biosynthetic genes using real-time quantitative polymerase chain reaction (Q-PCR). The results showed that the colors of both petals gradually weakened with flower development. Moreover, one main anthocyanin composition (peonidin 3,5-di-O-glucoside) and five main anthoxanthin compositions (kaempferol di-hexo-side, kaempferol-3-O-malonylglucoside-7-O-glucoside, quercetin-3-O-galactoside, luteolin-7-O-glucoside and isorhamnetin-3-O-glucoside) were found in the both, differing significantly in their peak areas only. Total anthocyanin, anthoxanthin and flavonoid contents in white outer-petal and yellow inner-petal gradually decreased during flower development, and were consistently higher in white outer-petal. Furthermore, the expression patterns of nine structural genes in P. lactiflora flavonoid biosynthetic pathway showed that the expression levels of phenylalanine ammonialyase gene (PIPAL), chalcone synthase gene (PICHS), flavanone 3-hydroxylase gene (PIF3H), anthocyanidin synthase gene (PIANS) and UDP-glucoside: flavonoid 5-O-glucosyltransferase gene (PIF5GT) in two petals basically presented declined tendencies, and transcription levels of PIPAL, PICHS, PIANS, PIF3GT and PIF5GT also tended to be higher in white outer-petal, which was correlated with their flavonoid contents. These results would lay a solid foundation for the exploration and utilization of flavonoid resources in P. lactiflora flowers.