Identification of novel C-glycosylflavones and their contribution to flower colour of the Dutch iris cultivars

Seventeen C-glycosylflavones including four novel ones, were isolated from the flowers of Dutch iris (Iris hollandica Hort. ex Todd.) cultivar ‘Blue Diamond’. Four new C-glycosylflavones were identified as isovitexin 2″-O-(4″′-acetylrhamnoside) (F1), swertisin 2″-O-(4″′-acetylrhamnoside) (F2), isovitexin 2″-O-(4″′-acetylrhamnoside)-4′-O-glucoside (F3) and swertisin 2″-O-(4″′-acetylrhamnoside)-4′-O-glucoside (F4) by UV spectra, LC–MS and 1H and 13C NMR. Furthermore, to understand the contribution of flavones to flower colour, the relationships with flower colours of three Dutch iris cultivars and flavonoid components were examined. The degree of blueness in the bluish cultivars ‘Blue Diamond’ and ‘Blue Magic’ were higher than that of the violet cultivar, ‘Yesterday’, and it was suggested that the flower colour expression from violet to blue colour of Dutch iris cultivars depend on the high ratio of total flavone contents/total delphinidin contents (F/A ratio). In addition, in vitro examination was carried out by the isolated anthocyanin and flavone. The mixture solutions were prepared in respective F/A ratio of three Dutch iris cultivars and could essentially reconstruct their visible absorption spectra of flowers. In conclusion, it was confirmed that isolated flavones contribute to blueness due to intermolecular co-pigmentation with anthocyanins.