Contribution of anthocyanin–flavone copigmentation to grayed violet flower color of Dutch iris cultivar ‘Tiger's Eye’ under the presence of carotenoids

• We surveyed the color expression in the grayed violet flowers of Dutch iris cultivar ‘Tiger's Eye’.
• We performed the measurement of absorption spectra and analyzed the pigments.
• We also performed the in vitro examination to identify the color expression.
• Anthocyanin–flavone copigmentation and carotenoids contribute to the flower color.

Dutch iris (Iris × hollandica) cultivar ‘Tiger's Eye’ (also known as ‘Eye of the Tiger’) has grayed violet falls and violet standards. In this study, we investigated the color expression of grayed violet falls and discussed contribution of copigmentation with anthocyanin and flavone to their color.Absorption spectral measurement and quantitative analysis were carried out using the falls and standards. Furthermore, distribution of each pigment was revealed by microscopic analysis using cross section of the falls. As the result, it was suggested that higher amount of carotenoid, which are present in the mesophyll tissue, and lower anthocyanin contents, which distribute to the epidermis, in the falls than those of the standards are related to grayed violet color expression.Furthermore, we performed in vitro examination using isolated anthocyanin [violanin; delphinidin 3-O-(4″′-p-coumaroylrutinoside)-5-O-glucoside] and flavone (swertiajaponin) and carotenoids extract. In this survey, grayed violet color was not expressed without the presence of flavone. It means that flavone contributes to the flower color of ‘Tiger's Eye’ as co-pigment in addition to anthocyanin. Chromaticity values of in vitro solution were measured and expressed as CIEL*a*b* space using digital images. The bluing effect was changed by copigmentation with carotenoids and associated lighter and duller appearance of the flower color.In conclusion, it was shown that the anthocyanin, flavone and carotenoids contribute to the expression of grayed violet falls of ‘Tiger's Eye’. It means that coexistence of the copigmentation and carotenoids is necessary to express their dullish color.

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