title: Specification of cortical parenchyma and stele of maize primary roots by asymmetric levels of auxin, cytokinin, and cytokinin-regulated proteins.
abstract: In transverse orientation, maize (Zea mays) roots are composed of a central stele that is embedded in multiple layers of cortical parenchyma. The stele functions in the transport of water, nutrients, and photosynthates, while the cortical parenchyma fulfills metabolic functions that are not very well characterized. To better understand the molecular functions of these root tissues, protein- and phytohormone-profiling experiments were conducted. Two-dimensional gel electrophoresis combined with electrospray ionization tandem mass spectrometry identified 59 proteins that were preferentially accumulated in the cortical parenchyma and 11 stele-specific proteins. Hormone profiling revealed preferential accumulation of indole acetic acid and its conjugate indole acetic acid-aspartate in the stele and predominant localization of the cytokinin cis-zeatin, its precursor cis-zeatin riboside, and its conjugate cis-zeatin O-glucoside in the cortical parenchyma. A root-specific beta-glucosidase that functions in the hydrolysis of cis-zeatin O-glucoside was preferentially accumulated in the cortical parenchyma. Similarly, four enzymes involved in ammonium assimilation that are regulated by cytokinin were preferentially accumulated in the cortical parenchyma. The antagonistic distribution of auxin and cytokinin in the stele and cortical parenchyma, together with the cortical parenchyma-specific accumulation of cytokinin-regulated proteins, suggest a molecular framework that specifies the function of these root tissues that also play a role in the formation of lateral roots from pericycle and endodermis cells.
authors.affiliation: Center for Plant Molecular Biology, Department of General Genetics, University of Tuebingen, 72076 Tuebingen, Germany.
authors.forename: Muhammad
authors.initials: M
authors.lastname: Saleem
authors.forename: Tobias
authors.initials: T
authors.lastname: Lamkemeyer
authors.forename: André
authors.initials: A
authors.lastname: Schützenmeister
authors.forename: Johannes
authors.initials: J
authors.lastname: Madlung
authors.forename: Hajime
authors.initials: H
authors.lastname: Sakai
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Piepho
authors.forename: Alfred
authors.initials: A
authors.lastname: Nordheim
authors.forename: Frank
authors.initials: F
authors.lastname: Hochholdinger
mesh_terms: D003583:Cytokinins / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D007210:Indoleacetic Acids / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000254:growth & development* / Q000378:metabolism; D018520:Plant Shoots / Q000201:enzymology; D036226:Seedlings / Q000201:enzymology; D015398:Signal Transduction; D003313:Zea mays / Q000254:growth & development* / Q000378:metabolism*; D001617:beta-Glucosidase / Q000235:genetics / Q000378:metabolism
chemical_list: D003583:Cytokinins; D007210:Indoleacetic Acids; D010940:Plant Proteins; D001617:beta-Glucosidase