Soybean flavonol glycosides: identification and biochemical genetics

Abstract

The products of controlled hydrolysis and oxidation of the flavonol 3-O-glycosides in soybean leaves were studied. From the study the kaempferol and quercetin glycosides were identified as the glucoside, sophoroside, gentiobioside, rutinoside, neohesperidoside, 2G-glucosylrutinoside, 2G-glucosylgentiobioside, 2G-rhamnosylrutinoside, and 2G-rhamnosylgentiobioside. The last three glycosides have not been reported before. The probable mode of biosynthesis is outlined; each of the four diglycosides is formed by a dominant flavonol glycoside gene, while the four triglycosides are formed by duplicate gene action. When glucose is added to the monoglucoside in the biosynthesis of diglycosides and triglycosides, Fg1 codes for a β(1–6) linkage and Fg3 codes for a β(1–2) linkage. Similarly, with rhamnose addition, Fg2 codes for an α(1–6) and Fg4 codes for an α(1–2) linkage. Hence, Fg1 or Fg2 can interact with Fg3 or Fg4 to form the branched triglycosides because they code for linkage to different carbons of the basic glucose unit. On the other hand Fg1 and Fg2 both code for a linkage to carbon-6 of the glucose, and Fg3 and Fg4 both add to carbon-2 of the glucose, thus there is no interaction within each of these pairs of genes to form branched triglycosides.