Co-pigmentation of Anthocyanin-flavonol in the Blotch Area of Rhododendron simsii Planch. Flowers

Abstract

Rhododendron simsii Planch. is distributed in eastern Asia, such as Ryukyu Islands of Japan, southern China, Taiwan, and Vietnam. It is a semideciduous shrub with five-lobed red corollas and reddish-purple blotches on the upper petals. From microscopic observation, reddish-purple colored cells were distributed only in the adaxial subepidermis of blotch areas in the upper petals, while red colored cells were observed in the whole epidermis of both upper and lower petals. Even though the anthocyanin constitutions of upper and lower petals were the same, the λ_max of absorbance of fresh upper petals was 514.9 nm, while it was 505.7 nm in the lower petals. In R. simsii flowers, cyanidin glycosides were major anthocyanins in whole petals. Quercetin glycosides were detected in reddish-purple blotch areas, but they were found only in trace amounts in lower petals. Anthocyanins and flavonols were extracted, and separated by column chromatography. Bathochromic shift (9.7 nm) was observed in mixed solution of anthocyanin and flavonol at a ratio of concentration of 1:7.5. These results were similar to the bathochromic shift obtained between upper and lower petals of intact flowers (9.2 nm). From these findings, co-pigmentation between anthocyanin and flavonol (quercetin glycosides) seems to be a key factor of reddish-purple color of the blotch area in the upper petals of R. simsii flowers.