JXB Advance Access published online on April 29, 2007
Journal of Experimental Botany, doi:10.1093/jxb/erm074
© 2007 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)
RESEARCH PAPER |
Cell elongation in Arabidopsis hypocotyls involves dynamic changes in cell wall thickness
Department of Cell and Developmental Biology, John Innes Centre, Colney, Norwich NR4 7UH, UK
To whom correspondence should be addressed. E-mail: keith.roberts{at}bbsrc.ac.uk
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 (
1 µm) 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.
Key words: Arabidopsis, cell wall, elongation, hypocotyl, pectin
* Present address: Department of Biological Sciences, Purdue University, West Lafayette, IN 47907, USA.
Received 7 February 2007; Revised 14 March 2007 Accepted 15 March 2007
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