Flavonols Regulate Plant Growth and Development through Regulation of Auxin Transport and Cellular Redox Status

Interest in the roles of flavonoids in fundamental biological processes has spurred an extensive characterization of their biosynthesis and demonstrated that specific metabolites in this pathway modulate a diversity of plant developmental and stress responses. Arabidopsis thaliana mutants with defects in flavonol biosynthesis have been used to demonstrate that flavonols modulate gravitropism, root elongation, root and inflorescence branching, and guard cell signaling to modulate stomatal aperture. In several cases, specific functions have been linked to individual flavonol derivatives. Mutants in flavonoid biosynthesis in other species share common phenotypes, but have also led to the identification of other functions of flavonols not found in Arabidopsis, such as fertilization and pollen viability. The molecular action of flavonols includes inhibition of auxin transport and antioxidant activity. The extensive environmental and hormonal regulation of flavonol biosynthesis, through transcriptional controls of genes encoding pathway enzymes, provides a mechanism to regulate the physiological processes modulated by flavonols.