Flavonoids of leguminous plants: Structure, biological activity, and biosynthesis

Flavonoids are common to most vascular plants and are postulated to be involved in a number of plant functions. Leguminous plants are intriguing materials for studies on flavonoids for several reasons. First, legumes produce flavonoids with specific chemical structures i.e. isoflavonoids and 5-deoxy(iso)flavonoids. Second, leguminous flavonoids are postulated to play important roles both as defensive compounds against pathogenic microorganisms and as chemical signals in symbiotic nitrogen fixation. Third, as constituents of food and forage, leguminous flavonoids have striking biological activity in humans and animals. This article reviews the chemical structure, biological activity, and biosynthesis of leguminous flavonoids. Recent achievements in the identification and characterization of cytochrome P450 monooxygenases, which play important roles in (iso) flavonoid biosynthesis, are also introduced. Perspectives of molecular genetic studies on flavonoids with the model legume are discussed.