Anthocyanin-flavone copigmentation in bluish purple flowers of Japanese garden iris (Iris ensata Thunb.)

Abstract

The in vitro identification of copigmentation was carried out using anthocyanins, such as malvidin 3RGac5G, petunidin 3RGac5G and delphinidin 3RGac5G and the flavone isovitexin. These are major pigments of Iris ensata. These anthocyanins brought about copigmentation, i.e., the bathochromic shift (bluing effect) of visible λ max due to increased concentrations of isovitexin, and 32 to 35 nm were estimated as the magnitude (Δλ max) of each shift. In addition, the absorption spectrum of 0.1 mM malvidin 3RGac5G, 0.07 mM petunidin 3RGac5G and 0.7 mM isovitexin mixture closely matched those of the fresh outer perianths of the bluish purple cultivars, ‘Suiten-isshoku’, ‘Hekikai’ and ‘Yakonotama’ which belong to the malvidin 3RGac5G - petunidin 3RGac5G type of I. ensata. Therefore, these results indicated that the bluing effect on the flower color of the bluish purple cultivars of this species was caused at least in part by the copigmentation between these anthocyanins and the flavone isovitexin. For the copigment effects of isovitexin among malvidin 3RGac5G, petunidin 3RGac5G and delphinidin 3RGac5G, λ max and Δλ max of delphinidin 3RGac5G was slightly higher than those of malvidin 3RGac5G or petunidin 3RGac5G, and the copigmentation of delphinidin 3RGac5G was characterized by a higher concentration of isovitexin. Finally, the breeding for blue flowers due to copigmentation of delphinidin 3RGac5G with isovitexin in I. ensata was discussed.