title: Zonal changes in ascorbate and hydrogen peroxide contents, peroxidase, and ascorbate-related enzyme activities in onion roots.
abstract: Onion (Allium cepa) roots growing hydroponically show differential zonal values for intra- (symplastic) and extra- (apoplastic) cellular ascorbate (ASC) and dehydroascorbate (DHA) contents and for related enzyme activities. In whole roots, ASC and DHA concentrations were higher in root apex and meristem and gradually decreased toward the root base. Guaiacol peroxidase, ASC peroxidase, monodehydroascorbate oxidoreductase, DHA reductase, catalase, and glutathione reductase activities showed differential activity patterns depending on the zone of the root and their apoplastic or symplastic origin. An in vivo staining of peroxidase activity also revealed a specific distribution pattern along the root axis. Using electron microscopy, hydrogen peroxide was found at different locations depending on the root zone but was mainly located in cell walls from epidermal and meristematic cells and in cells undergoing lignification. A balanced control of all of these molecules seems to exist along the root axis and may be directly related to the mechanisms in which the ASC system is involved, as cell division and elongation. The role of ASC on growth and development in relation to its presence at the different zones of the root is discussed.
authors.affiliation: Departamento de Biología Celular, Fisiología e Inmunología, University of Córdoba, 14014 Córdoba, Spain.
authors.forename: María
authors.initials: M
authors.lastname: Del Carmen Córdoba-Pedregosa
authors.forename: Francisco
authors.initials: F
authors.lastname: Córdoba
authors.forename: José Manuel
authors.initials: JM
authors.lastname: Villalba
authors.forename: José Antonio
authors.initials: JA
authors.lastname: González-Reyes
mesh_terms: D060387:Ascorbate Peroxidases; D001205:Ascorbic Acid / Q000378:metabolism*; D002374:Catalase / Q000378:metabolism; D003683:Dehydroascorbic Acid / Q000378:metabolism; D004798:Enzymes / Q000378:metabolism*; D005980:Glutathione Reductase / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000378:metabolism*; D018519:Meristem / Q000166:cytology / Q000378:metabolism / Q000648:ultrastructure; D008854:Microscopy, Electron; D009247:NADH, NADPH Oxidoreductases / Q000378:metabolism; D019697:Onions / Q000201:enzymology / Q000378:metabolism*; D010088:Oxidoreductases / Q000378:metabolism; D009195:Peroxidase / Q000378:metabolism*; D010544:Peroxidases / Q000378:metabolism; D018517:Plant Roots / Q000166:cytology / Q000201:enzymology / Q000378:metabolism*
chemical_list: D004798:Enzymes; D006861:Hydrogen Peroxide; D010088:Oxidoreductases; D010544:Peroxidases; C121048:guaiacol peroxidase; D060387:Ascorbate Peroxidases; D002374:Catalase; D009195:Peroxidase; D009247:NADH, NADPH Oxidoreductases; C023927:monodehydroascorbate reductase (NADH); D005980:Glutathione Reductase; C020666:glutathione dehydrogenase (ascorbate); D001205:Ascorbic Acid; D003683:Dehydroascorbic Acid