Identification of novel flower anthocyanins of Delphinium grandiflorum cultivars

Abstract

Flower color is one of the most important properties of ornamental flowers. Information on the kinds of pigments that flowers can biosynthesize is useful for breeding cultivars focused on flower colors. The flower colors of regular ornamental delphinium cultivars are blue, violet, purple, pink, and white. The pigments of these flowers are delphinidin-based anthocyanins. It has been reported that the typical modification in delphinium anthocyanins involves the transfer of glucose and p-hydroxybenzoic acid molecules to the 7-position of delphinidin one by one, and it was predicted that other unidentified anthocyanins are present in addition to the already reported ones. Recently, light pink flowers that accumulate pelargonidin-based anthocyanins were reported from cultivars derived from Delphinium grandiflorum. Converting delphinidin-based anthocyanins to pelargonidin-based ones is considered key to producing red flowers in delphinium. Hence, we investigated anthocyanins of blue, mauve, light pink, and white flowers of D. grandiflorum cultivars. We isolated anthocyanins and analyzed them using HPLC, TLC, UV–vis spectra, FABMS, and NMR. Using these methods, we identified two novel delphinidin-based anthocyanins and three novel pelargonidin-based anthocyanins: delphinidin 3-O-[6-O-(α-rhamnopyranosyl)-β-glucopyranoside]-7-O-[6-O-(p-hydroxybenzoyl)-β-glucopyranoside] (2), pelargonidin 3-O-[6-O-(α-rhamnopyranosyl)-β-glucopyranoside]-7-O-[6-O-(4-O-(6-O-(p-hydroxybenzoyl)-β-glucopyranosyl)-p-hydroxybenzoyl)-β-glucopyranoside] (5, rubrodelphin), pelargonidin 3-O-[6-O-(α-rhamnopyranosyl)-β-glucopyranoside]-7-O-[3-O-(β-glucopyranosyl)-6-O-(4-O-(6-O-(p-hydroxybenzoyl)-β-glucopyranosyl)-p-hydroxybenzoyl)-β-glucopyranoside] (6), delphinidin 3-O-[6-O-(α-rhamnopyranosyl)-β-glucopyranoside]-7-O-[3-O-(3-O-(6-O-(p-hydroxybenzoyl)-β-glucopyranosyl)-β-glucopyranosyl)-6-O-(4-O-(6-O-(p-hydroxybenzoyl)-β-glucopyranosyl)-p-hydroxybenzoyl)-β-glucopyranoside] (7), and pelargonidin 3-O-[6-O-(α-rhamnopyranosyl)-β-glucopyranoside]-7-O-[3-O-(3-O-(6-O-(4-O-(6-O-(p-hydroxybenzoyl)-β-glucopyranosyl)-p-hydroxybenzoyl)-β-glucopyranosyl)-β-glucopyranosyl)-6-O-(4-O-(6-O-(p-hydroxybenzoyl)-β-glucopyranosyl)-p-hydroxybenzoyl)-β-glucopyranoside] (9, rosedelphin), along with four known anthocyanins. The flowers of five blue cultivars accumulated cyanodelphin (8) as the dominant pigment. The shapes of visible absorption spectra of these five blue flowers were similar, indicating that the color and the absorption spectra were the typical ones for delphinium blue color produced by 8. The mauve flower color was due to a mixture of delphinidin-based anthocyanins in various polyacylated levels at the 7-position. The light pink flowers accumulated pelargonidin-based anthocyanins 5, 6, and 9. These pigment structures showed that the pelargonidin-based anthocyanins modified in the same way as in the originally biosynthesized delphinidin-based anthocyanins even though aglycone was replaced by pelargonidin in these anthocyanins.