Most flower color is caused by anthocyanins.Anthocyanins are dissolved in vacuoles of epidermal cells. The color of anthocyanins changes depending pH and concentration of pigment,co-pigment and metal ions.To clarify the mechanism of flower color development and variation in living petal cell we measured absorption spectrum of colored protoplast and the vacuolar pH of the same cell by using proton selective microelectrode.We also analyzed the organic components and metal ions in the colored vacuoles.Using those techniques we studied the color change and the difference of blue and red hydrangea sepals.
Hydrangea flower color is varied from red,through purple to blue.However,all colors are caused from the same pigment,delphinidin 3-glucoside (1)and the same co-pigments,5-O-caffeoylquinic acid(2),5-O-p-coumaroylquinic acid(3),and 3-O-caffeoylquinic acid(4),with Al³⁺ ion.From the sepal tissue we isolated colored protoplasts.The vacuolar pH of blue cell was 4.1 and that of red cell was 3.3.The Molar ratio of components(1:2:3:4: Al³⁺ )in blue cells was 1:7:3:9:1.On the other hand that in red cells was 1:2:1:16:0.01.From those in vivo data we could reconstruct both blue and red color hydrangea sepals.