title: Flavonoids as antioxidants in plants: location and functional significance.
abstract: Stress-responsive dihydroxy B-ring-substituted flavonoids have great potential to inhibit the generation of reactive oxygen species (ROS) and reduce the levels of ROS once they are formed, i.e., to perform antioxidant functions. These flavonoids are located within or in the proximity of centers of ROS generation in severely stressed plants. Efficient mechanisms have been recently identified for the transport of flavonoids from the endoplasmic reticulum, the site of their biosynthesis, to different cellular compartments. The mechanism underlying flavonoid-mediated ROS reduction in plants is still unclear. 'Antioxidant' flavonoids are found in the chloroplast, which suggests a role as scavengers of singlet oxygen and stabilizers of the chloroplast outer envelope membrane. Dihydroxy B-ring substituted flavonoids are present in the nucleus of mesophyll cells and may inhibit ROS-generation making complexes with Fe and Cu ions. The genes that govern the biosynthesis of antioxidant flavonoids are present in liverworts and mosses and are mostly up-regulated as a consequence of severe stress. This suggests that the antioxidant flavonoid metabolism is a robust trait of terrestrial plants. Vacuolar dihydroxy B-ring flavonoids have been reported to serve as co-substrates for vacuolar peroxidases to reduce H(2)O(2) escape from the chloroplast, following the depletion of ascorbate peroxidase activity. Antioxidant flavonoids may effectively control key steps of cell growth and differentiation, thus acting regulating the development of the whole plant and individual organs.
authors.affiliation: Consiglio Nazionale delle Ricerche, Istituto di Fisica Applicata 'Carrara', Via Madonna del Piano 10, I-50019 Sesto F. No, Firenze, Italy.
authors.forename: Giovanni
authors.initials: G
authors.lastname: Agati
authors.forename: Elisa
authors.initials: E
authors.lastname: Azzarello
authors.forename: Susanna
authors.initials: S
authors.lastname: Pollastri
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Tattini
mesh_terms: D000975:Antioxidants / Q000737:chemistry / Q000378:metabolism*; D001692:Biological Transport; D002467:Cell Nucleus / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005419:Flavonoids / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D008954:Models, Biological; D015394:Molecular Structure; D010944:Plants / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism*; D014617:Vacuoles / Q000378:metabolism
chemical_list: D000975:Antioxidants; D005419:Flavonoids; D017382:Reactive Oxygen Species