JXB Advance Access originally published online on January 10, 2005
Journal of Experimental Botany 2005 56(412):673-683; doi:10.1093/jxb/eri048
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RESEARCH PAPER |
XTH acts at the microfibrilmatrix interface during cell elongation
1University of Antwerp (Drie Eiken Campus), Department of Biology, Plant Physiology and Morphology, Universiteitsplein 1, 2610 Wilrijk, Belgium
2The Edinburgh Cell Wall Group, Institute of Molecular Plant Sciences, School of Biological Sciences, The University of Edinburgh, Daniel Rutherford Building, The King's Buildings, Edinburgh EH9 3JH, UK
3Max-Planck-Institute of Molecular Plant Physiology, Am Mühlenberg 1, D-14476 Golm, Germany
4INRA, Laboratoire de Biologie Cellulaire, Route de St Cyr, F-78026 Versailles Cédex, France
* To whom correspondence should be addressed. Fax: +32 3 820 22 71. E-mail: kris.vissenberg{at}ua.ac.be
Sulphorhodamine-labelled oligosaccharides of xyloglucan are incorporated into the cell wall of Arabidopsis and tobacco roots, and of cultured Nicotiana tabacum cells by the transglucosylase (XET) action of XTHs. In the cell wall of diffusely growing cells, the subcellular pattern of XET action revealed a fibrillar pattern, different from the xyloglucan localization. The fibrillar fluorescence pattern had no net orientation in spherical cultured cells. It changed to transverse to the long axis when the cells started to elongate, a feature mirroring the rearrangements of cortical microtubules and the accompanying cellulose deposition. Interference with the polymerization of microtubules and with cellulose deposition inhibited this strong and fibrillar-organized XET-action, whereas interference with actin-polymerization only decreased the intensity of enzyme action. Epidermal cells of a mutant with reduced cellulose synthesis also had low XET action. Root hairs (tip-growing cells) exhibited high XET-action over all their length, but lacked the specific parallel pattern. In both diffuse- and tip-growing cell types extraction of the incorporated fluorescent xyloglucans by a xyloglucan-specific endoglucanase reduced the fluorescence, but the fibrillar appearance in diffuse growing cells was not eliminated. These results show that XTHs act on the xyloglucans attached to cellulose microfibrils. After incorporation of the fluorescent oligosaccharides, the xyloglucans decorate the cellulose microfibrils and become inaccessible to hydrolytic enzymes.
Key words: Cell wall, confocal laser scanning microscopy, expansion, growth, xyloglucan endotransglucosylase/hydrolase (XTH)
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