Pigments Composition of Petals and Floral Color Change During the Blooming Period in Rhododendron mucronulatum

Abstract

The floral color of Rhododendron mucronulatum Turcz. was investigated in terms of its presentation, pigments composition, changes in the composition during blooming season. The floral color was measured according to the Royal Horticultural Society Colour Chart (RHSCC) and then by a NF333 spectrophotometer. The results indicated that floral lightness increased, while the value of chroma decreased during the blooming period, and floral color turned from red purple (70B) to violet (84B) at the meantime. A high performance liquid chromatography with a photodiode array detector (HPLC-PAD) and HPLC electrospray ionization mass spectrometry (HPLC-ESI-MS) methods were employed for qualitative and quantitative analysis of anthocyanins and flavonols. In total, 15 compounds were detected at 520 nm and 350 nm in the petals: five anthocyanins, eight flavonols and two aromatic acids. Ten of them were tentatively identified, including one anthocyanin (malvidin 3-arabinoside-5-glucoside), eight flavonols (myricetin 3-galactoside, myricetin 3-rhamnoside, quercetin 3-galactoside, quercetin 3-glucoside, two quercetin-rhamnosides and kaempferol 3-rhamnoside), and two aromatic acid (chlorogenic acid and its isomer). No acylated pigments and 5-O-methylated flavonols were detected. Although the floral color changed significantly in the six blooming stages, the pigment composition kept unchanged, and the pigment content showed significant difference from the initiation of floral buds to the late opening of flowers. Total anthocyanins content (TA) and total flavonols content (TF) decreased rapidly during the first three stages, and then changed smoothly. The floral color breeding strategies for cultivars with cold resistance were discussed based on the pigment composition of R. mucronulatum.