2022 Volume 21 Issue 1 Pages 73-81
Hydrangea sepals show seasonal coloration change. They express red and blue as the summer color due to a delphinidin-based anthocyanin. Through changing to green color, they newly express red or purple as the autumn color. Recently, the horticultural value of Hydrangea expressing the autumn color has increased. We studied pigment biosynthesis and the coloration mechanism of autumn color expression. The pigments responsible for autumn color were cyanidin-based anthocyanins including cyanidin 3-lathyroside, which was newly detected as a main pigment of sepals in this study. The autumn color could not be expressed in shaded parts and was uniformly expressed even in sepals that display a marginal picotee pattern in the summer color. The pigment biosynthetic mechanisms of autumn and summer color expression differ in terms of the anthocyanin structure including chromophores, light requirement, and tissue specificity. In contrast, the coloration mechanisms of autumn and summer colors were similar; i.e., the blue color was generated by the formation of a chelate structure of aluminum ion by anthocyanin and 5-O-caffeoylquinic acid, while the red color was possibly generated by involvement of a compound that inhibits the formation of this chelate structure. This similarity causes the corresponding tone of autumn and summer colors in the same plant.
