title: Brassinosteroids promote root growth in Arabidopsis.
abstract: Although brassinosteroids (BRs) are known to regulate shoot growth, their role in the regulation of root growth is less clear. We show that low concentrations of BRs such as 24-epicastasterone and 24-epibrassinolide promote root elongation in Arabidopsis wild-type plants up to 50% and in BR-deficient mutants such as dwf1-6 (cbb1) and cbb3 (which is allelic to cpd) up to 150%. The growth-stimulating effect of exogenous BRs is not reduced by the auxin transport inhibitor 2,3,5-triidobenzoic acid. BR-deficient mutants show normal gravitropism, and 2,3,5-triidobenzoic acid or higher concentrations of 2,4-dichlorophenoxyacetic acid and naphtaleneacetic acid inhibit root growth in the mutants to the same extent as in wild-type plants. Simultaneous administration of 24-epibrassinolide and 2,4-dichlorophenoxyacetic acid results in largely additive effects. Exogenous gibberellins do not promote root elongation in the BR-deficient mutants, and the sensitivity to the ethylene precursor 1-aminocyclopropane-1-carboxylic acid is not altered. Thus, the root growth-stimulating effect of BRs appears to be largely independent of auxin and gibberellin action. Furthermore, we analyzed BR interactions with other phytohormones on the gene expression level. Only a limited set of auxin- and ethylene-related genes showed altered expression levels. Genes related to other phytohormones barely showed changes, providing further evidence for an autonomous stimulatory effect of BR on root growth.
authors.affiliation: Universität Potsdam, Institut für Biochemie und Biologie, Genetik, c/o Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenberg 1, 14476 Golm, Germany. muessig@mpimp-golm.mpg.de
authors.forename: Carsten
authors.initials: C
authors.lastname: Müssig
authors.forename: Ga-Hee
authors.initials: GH
authors.lastname: Shin
authors.forename: Thomas
authors.initials: T
authors.lastname: Altmann
mesh_terms: D000598:Amino Acids, Cyclic / Q000494:pharmacology; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000254:growth & development*; D060406:Brassinosteroids; D002777:Cholestanols / Q000494:pharmacology*; D004347:Drug Interactions / Q000502:physiology; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D005875:Gibberellins / Q000494:pharmacology; D007210:Indoleacetic Acids / Q000494:pharmacology; D009154:Mutation; D010937:Plant Growth Regulators / Q000494:pharmacology*; D018517:Plant Roots / Q000187:drug effects / Q000254:growth & development*; D013260:Steroids, Heterocyclic / Q000494:pharmacology*
chemical_list: D000598:Amino Acids, Cyclic; D060406:Brassinosteroids; D002777:Cholestanols; D005875:Gibberellins; D007210:Indoleacetic Acids; D010937:Plant Growth Regulators; D013260:Steroids, Heterocyclic; C023863:1-aminocyclopropane-1-carboxylic acid; C083545:castasterone; C023623:brassinolide