Flavonoids: signal molecules in plant development.

Abstract

More than 4,000 different flavonoids, which are widely distributed in higher plants, have been identified (Harborne, 1988; Koes et al. 1994). Flavonoids are involved in numerous functions in vascular plants. One obvious function is as a filter for ultraviolet light, which requires that there be relatively large concentrations of flavonoids in epidermal cells (Li et al.,1993). Flavonoids also function as external chemical signals for symbiotic nitrogen fixation (Fisher and Long, 1992; Baker, 1992) and for mycorrhizal relationships (Vierheilig et al.,1998). Flavonoids are also important in fighting disease; ingress of pathogenic microbes can be curtailed in certain incompatible reactions in part because some plants synthesize flavonoid phytoalexins (Dixon and Paiva, 1995). Anthocyanidins and their glycosides, accumulating mainly in the inner epidermis of the petal just prior to opening of the flower bud, attract insect and other agents for pollination (Weiss, 1991). Later on, as the fruit develops, flavonoids can also attract agents for seed dispersal.