title: Auxin acts in xylem-associated or medullary cells to mediate apical dominance.
abstract: A role for auxin in the regulation of shoot branching was described originally in the Thimann and Skoog model, which proposes that apically derived auxin is transported basipetally directly into the axillary buds, where it inhibits their growth. Subsequent observations in several species have shown that auxin does not enter axillary buds directly. We have found similar results in Arabidopsis. Grafting studies indicated that auxin acts in the aerial tissue; hence, the principal site of auxin action is the shoot. To delineate the site of auxin action, the wild-type AXR1 coding sequence, which is required for normal auxin sensitivity, was expressed under the control of several tissue-specific promoters in the auxin-resistant, highly branched axr1-12 mutant background. AXR1 expression in the xylem and interfascicular schlerenchyma was found to restore the mutant branching to wild-type levels in both intact plants and isolated nodes, whereas expression in the phloem did not. Therefore, apically derived auxin can suppress branching by acting in the xylem and interfascicular schlerenchyma, or in a subset of these cells.
authors.affiliation: The Plant Laboratory, Department of Biology, University of York, P.O. Box 373, York YO10 5YW, United Kingdom.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Booker
authors.forename: Steven
authors.initials: S
authors.lastname: Chatfield
authors.forename: Ottoline
authors.initials: O
authors.lastname: Leyser
mesh_terms: D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000254:growth & development*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D005816:Genetic Complementation Test; D006133:Growth Substances / Q000235:genetics / Q000378:metabolism; D007210:Indoleacetic Acids / Q000494:pharmacology* / Q000502:physiology; D009154:Mutation; D010641:Phenotype; D010937:Plant Growth Regulators / Q000494:pharmacology / Q000502:physiology; D018520:Plant Shoots / Q000187:drug effects / Q000254:growth & development*; D011401:Promoter Regions, Genetic / Q000235:genetics
chemical_list: C081977:AXR1 protein, Arabidopsis; D029681:Arabidopsis Proteins; D006133:Growth Substances; D007210:Indoleacetic Acids; D010937:Plant Growth Regulators