title: Cell elongation in Arabidopsis hypocotyls involves dynamic changes in cell wall thickness.
abstract: Field-emission scanning electron microscopy was used to measure wall thicknesses of different cell types in freeze-fractured hypocotyls of Arabidopsis thaliana. Measurements of uronic acid content, wall mass, and wall volume suggest that cell wall biosynthesis in this organ does not always keep pace with, and is not always tightly coupled to, elongation. In light-grown hypocotyls, walls thicken, maintain a constant thickness, or become thinner during elongation, depending upon the cell type and the stage of growth. In light-grown hypocotyls, exogenous gibberellic acid represses the extent of thickening and promotes cell elongation by both wall thinning and increased anisotropy during the early stages of hypocotyl elongation, and by increased wall deposition in the latter stages. Dark-grown hypocotyls, in the 48 h period between cold imbibition and seedling emergence, deposit very thick walls that subsequently thin in a narrow developmental window as the hypocotyl rapidly elongates. The rate of wall deposition is then maintained and keeps pace with cell elongation. The outer epidermal wall is always the thickest ( approximately 1 mum) whereas the thinnest walls, about 50 nm, are found in inner cell layers. It is concluded that control of wall thickness in different cell types is tightly regulated during hypocotyl development, and that wall deposition and cell elongation are not invariably coupled.
authors.affiliation: Department of Cell and Developmental Biology, John Innes Centre, Colney, Norwich NR4 7UH, UK.
authors.forename: Paul
authors.initials: P
authors.lastname: Derbyshire
authors.forename: Kim
authors.initials: K
authors.lastname: Findlay
authors.forename: Maureen C
authors.initials: MC
authors.lastname: McCann
authors.forename: Keith
authors.initials: K
authors.lastname: Roberts
mesh_terms: D017360:Arabidopsis / Q000166:cytology* / Q000187:drug effects / Q000254:growth & development; D049108:Cell Enlargement / Q000187:drug effects; D002473:Cell Wall / Q000648:ultrastructure*; D005875:Gibberellins / Q000494:pharmacology; D018546:Hypocotyl / Q000166:cytology* / Q000187:drug effects / Q000254:growth & development; D008027:Light; D008855:Microscopy, Electron, Scanning; D012639:Seeds / Q000166:cytology / Q000187:drug effects / Q000254:growth & development
chemical_list: D005875:Gibberellins; C007842:gibberellic acid