5,7,3\u02b9,4\u02b9-Tetrahydroxyflav-2-en-3-ol 3-O-glucoside, a new biosynthetic precursor of cyanidin 3-O-glucoside in the seed coat of black soybean, Glycine max

Kumi Yoshida,Emi Hayashi,Tadao Kondo,Yuhsuke Nakane,Reo Sawaguchi,Yada Teppabut,Yukihiro Goda,Yuzo Nishizaki,Kin-Ichi Oyama

doi:10.1038/s41598-020-74098-6

Kumi Yoshida, Emi Hayashi + Show 7 more

Open Access

https://doi.org/10.1038/s41598-020-74098-6

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Abstract

The seed coat of mature black soybean, Glycine max, accumulates a high amount of cyanidin 3-O-glucoside (Cy3G), which is the most abundant anthocyanin in nature. In the pod, it takes two months for the seed coat color change from green to black. However, immature green beans rapidly adopt a black color within one day when the shell is removed. We analyzed the components involved in the color change of the seed coat and detected a new precursor of Cy3G, namely 5,7,3ʹ,4ʹ-tetrahydroxyflav-2-en-3-ol 3-O-glucoside (2F3G). Through quantitative analysis using purified and synthetic standard compounds, it was clarified that during this rapid color change, an increase in the Cy3G content was observed along with the corresponding decrease in the 2F3G content. Chemical conversion from 2F3G to Cy3G at pH 5 with air and ferrous ion was observed. Our findings allowed us to propose a new biosynthetic pathway of Cy3G via a colorless glucosylated compound, 2F3G, which was oxidized to give Cy3G.

Highlights

Anthocyanins are plant pigments which are often responsible for the colors of flowers, fruits, vegetables, and roots, with such colors ranging widely from red through purple to blue[1,2,3,4]
Since we are interested in the reaction mechanism involved in the transformation of leucocyanidin to cyanidin, we undertook the chemical synthesis of cyanidin 3-O-glucoside (Cy3G) (1) and found that the oxidation of a cis-leucocyanidin derivative did not give Cy3G (1), but delivered a red-colored p olymer[32]
Rapid color change in the seed coat of immature black soybeans removed from the pod

Summary

Introduction

Anthocyanins are plant pigments which are often responsible for the colors of flowers, fruits, vegetables, and roots, with such colors ranging widely from red through purple to blue[1,2,3,4]. We determined the levels of Cy3G (1) and 2F3G (2) present in the immature seed coats and monitored their contents during the rapid color change.

Results

Conclusion