title: Phloem-transported cytokinin regulates polar auxin transport and maintains vascular pattern in the root meristem.
abstract: Cytokinin phytohormones regulate a variety of developmental processes in the root such as meristem size, vascular pattern, and root architecture [1-3]. Long-distance transport of cytokinin is supported by the discovery of cytokinins in xylem and phloem sap [4] and by grafting experiments between wild-type and cytokinin biosynthesis mutants [5]. Acropetal transport of cytokinin (toward the shoot apex) has also been implicated in the control of shoot branching [6]. However, neither the mode of transport nor a developmental role has been shown for basipetal transport of cytokinin (toward the root apex). In this paper, we combine the use of a new technology that blocks symplastic connections in the phloem with a novel approach to visualize radiolabeled hormones in planta to examine the basipetal transport of cytokinin. We show that this occurs through symplastic connections in the phloem. The reduction of cytokinin levels in the phloem leads to a destabilization of the root vascular pattern in a manner similar to mutants affected in auxin transport or cytokinin signaling [7]. Together, our results demonstrate a role for long-distance basipetal transport of cytokinin in controlling polar auxin transport and maintaining the vascular pattern in the root meristem.
authors.affiliation: Institute of Biotechnology and Department of Biosciences, University of Helsinki, FIN-00014 Helsinki, Finland.
authors.forename: Anthony
authors.initials: A
authors.lastname: Bishopp
authors.forename: Satu
authors.initials: S
authors.lastname: Lehesranta
authors.forename: Anne
authors.initials: A
authors.lastname: Vatén
authors.forename: Hanna
authors.initials: H
authors.lastname: Help
authors.forename: Sedeer
authors.initials: S
authors.lastname: El-Showk
authors.forename: Ben
authors.initials: B
authors.lastname: Scheres
authors.forename: Kerttuli
authors.initials: K
authors.lastname: Helariutta
authors.forename: Ari Pekka
authors.initials: AP
authors.lastname: Mähönen
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Sakakibara
authors.forename: Ykä
authors.initials: Y
authors.lastname: Helariutta
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D001692:Biological Transport; D003583:Cytokinins / Q000378:metabolism*; D007210:Indoleacetic Acids / Q000378:metabolism*; D018519:Meristem / Q000254:growth & development / Q000378:metabolism*; D052585:Phloem / Q000378:metabolism*; D010937:Plant Growth Regulators / Q000378:metabolism*; D018517:Plant Roots / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D003583:Cytokinins; D007210:Indoleacetic Acids; D010937:Plant Growth Regulators