title: An auxin gradient and maximum in the Arabidopsis root apex shown by high-resolution cell-specific analysis of IAA distribution and synthesis.
abstract: Local concentration gradients of the plant growth regulator auxin (indole-3-acetic acid [IAA]) are thought to instruct the positioning of organ primordia and stem cell niches and to direct cell division, expansion, and differentiation. High-resolution measurements of endogenous IAA concentrations in support of the gradient hypothesis are required to substantiate this hypothesis. Here, we introduce fluorescence-activated cell sorting of green fluorescent protein-marked cell types combined with highly sensitive mass spectrometry methods as a novel means for analyses of IAA distribution and metabolism at cellular resolution. Our results reveal the presence of IAA concentration gradients within the Arabidopsis thaliana root tip with a distinct maximum in the organizing quiescent center of the root apex. We also demonstrate that the root apex provides an important source of IAA and that cells of all types display a high synthesis capacity, suggesting a substantial contribution of local biosynthesis to auxin homeostasis in the root tip. Our results indicate that local biosynthesis and polar transport combine to produce auxin gradients and maxima in the root tip.
authors.affiliation: Department of Forest Genetics, Umeå Plant Science Centre, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden.
authors.forename: Sara V
authors.initials: SV
authors.lastname: Petersson
authors.forename: Annika I
authors.initials: AI
authors.lastname: Johansson
authors.forename: Mariusz
authors.initials: M
authors.lastname: Kowalczyk
authors.forename: Alexander
authors.initials: A
authors.lastname: Makoveychuk
authors.forename: Jean Y
authors.initials: JY
authors.lastname: Wang
authors.forename: Thomas
authors.initials: T
authors.lastname: Moritz
authors.forename: Markus
authors.initials: M
authors.lastname: Grebe
authors.forename: Philip N
authors.initials: PN
authors.lastname: Benfey
authors.forename: Göran
authors.initials: G
authors.lastname: Sandberg
authors.forename: Karin
authors.initials: K
authors.lastname: Ljung
mesh_terms: D017360:Arabidopsis / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D048429:Cell Size; D005434:Flow Cytometry; D049452:Green Fluorescent Proteins / Q000032:analysis; D006706:Homeostasis; D007210:Indoleacetic Acids / Q000378:metabolism*; D013058:Mass Spectrometry / Q000379:methods; D018517:Plant Roots / Q000166:cytology / Q000378:metabolism; D011523:Protoplasts / Q000378:metabolism
chemical_list: D007210:Indoleacetic Acids; D049452:Green Fluorescent Proteins