Tracing the genealogy of research on the mechanism of blue flower coloration by anthocyanin based on Keita Shibata's work

Abstract

K. Shibata is the ancestor of the research on anthocyanins in Japan and proposed metal complex theory against the pH theory by R. Willstätter. Shibata's successors, S. Hattori and K. Hayashi, made efforts to clarify blue flower coloration by metal complexation and found commelinin, a self-assembled supramolecular metal complex pigment, in blue dayflower, Tsuyukusa. The author introduces two key reports on blue flower coloration published in the Proceedings of the Japan Academy and describes the subsequent development of the study.

Keywords: anthocyanin; blue flower coloration; commelinin; crystallographic analysis; metalloanthocyanin.

Fig. 1

Structure of common anthocyanins and the aglycones, anthocyanidins.

Fig. 2

Structure change of anthocyanin chromophore depending on pH and color.

Photo 1

Photos of Keita Shibata (left) and Yuji Shibata (right), donated from Japan Academy.

Fig. 3

Wild Tsuyukusa flower (right) and cultivated Ooboshibana (left).

Fig. 4

Photos of blue crystals of commelinin: taken from the publication in 1959 (left) and the SEM image of the crystal for X-ray crystallographic analysis in the publication in 1992 (right).

Fig. 5

Absorption spectra of commelinin and acid-treated commelinin taken from the publication in 1959.

Fig. 6

Organic components of commelinin: malonylawobanin (left) and flavocommelin (right).

Fig. 7

X-ray crystallographic structure of commelinin: the entire structure of commelinin (left) and the stacking structure of two anthocyanins (right). Each anthocyanin chelates to different metal ions. Blue, malonylawobanins; yellow, flavocommelin; red circle, Cd²⁺ (from Kondo et al., Nature 358, 515–518).