Change of color and components in sepals of chameleon hydrangea during maturation and senescence

The sepal color of a chameleon hydrangea, Hydrangea macrophylla cv. Hovariatrade mark 'Homigo' changes in four stages, from colorless to blue, then to green, and finally to red, during maturation and the senescence periods. To clarify the chemical mechanism of the color change, we analyzed the components of the sepals at each stage. Blue-colored sepals contained 3-O-sambubiosyl- and 3-O-glucosyldelphinidin along with three co-pigments, 5-O-p-coumaroyl-, 5-O-caffeoyl- and 3-O-caffeoylquinic acids. The contents of glycosyldelphinidins decreased toward the green-colored stage, with a coincident increase in the number of chloroplasts. During the last red colored stage, the two species of 3-O-glycosyldelphinidin almost disappeared, and another two anthocyanins, 3-O-sambubiosyl- and 3-O-glucosylcyanidin, increased in amounts. Mixing of 3-O-glycosylcyanidins, co-pigments, and Al3+ in a buffered solution at pH 3.0-3.5 gave not a blue, but a red, colored solution that was the same as that of the sepal color of the 4th stage. Sepals of hydrangea grown in an highland area also turned red in autumn, and contained the same cyanidin glycosides. The red coloration of the hydrangea during senescence was due to a change in anthocyanin biosynthesis.