A Peculiar Yellow Flower Coloration of Camellia Using Aluminum-flavonoid Interaction

The yellow coloration mechanism of Camellia chrysantha flowers has been a mystery because the pigments which produce their deep yellow color could not be found in the flower. We sought to solve the mystery regarding the characteristic accumulation of aluminum ions by camellia plants. Deep yellow C. chrysantha flowers contained aluminum ions at three times the concentration found in pale yellow flowers. Three quercetin derivatives, 3-rutinoside, 3-glucoside, and 7-glucoside, were identified as major flavonoids in both flowers. There were no significant differences in their flavonoid content or pH, which was 5.8. The deep yellow flowers of C. chrysantha contained flavonoids and aluminum ions in a ratio of 1 to 0.5. When quercetin 3-rutinoside solution, which was originally almost colorless and had an absorption maximum around 350 nm at pH 5.8, was prepared with an aluminum ion concentration similar to the endogenous ratio, the solution developed a deep yellow color. This mixture also had an absorption spectrum like that of C. chrysantha petals, which had an absorption maximum around 420 nm. After removing the cations using an ion exchange column, the yellow coloration of the C. chrysantha petal extract changed to a paler color; the coloration was restored by the addition of aluminum ions. We concluded that the deep yellow color of the C. chrysantha flower is generated by the chelation of aluminum ions by quercetin derivatives, which is a unique yellow ‘dyeing’ system of these flowers.