First published online August 6, 2004; 10.1104/pp.104.040493
Plant Physiology 135:2279-2290 (2004)
© 2004 American Society of Plant Biologists
DEVELOPMENT AND HORMONE ACTION
Disorganization of Cortical Microtubules Stimulates Tangential Expansion and Reduces the Uniformity of Cellulose Microfibril Alignment among Cells in the Root of Arabidopsis1
Tobias I. Baskin2,*,
Gerrit T.S. Beemster3,
Jan E. Judy-March and
Françoise Marga
Division of Biological Sciences, University of Missouri, Columbia, Missouri 65211
To test the role of cortical microtubules in aligning cellulose microfibrils and controlling anisotropic expansion, we exposed Arabidopsis thaliana roots to moderate levels of the microtubule inhibitor, oryzalin. After 2 d of treatment, roots grow at approximately steady state. At that time, the spatial profiles of relative expansion rate in length and diameter were quantified, and roots were cryofixed, freeze-substituted, embedded in plastic, and sectioned. The angular distribution of microtubules as a function of distance from the tip was quantified from antitubulin immunofluorescence images. In alternate sections, the overall amount of alignment among microfibrils and their mean orientation as a function of position was quantified with polarized-light microscopy. The spatial profiles of relative expansion show that the drug affects relative elongation and tangential expansion rates independently. The microtubule distributions averaged to transverse in the growth zone for all treatments, but on oryzalin the distributions became broad, indicating poorly organized arrays. At a subcellular scale, cellulose microfibrils in oryzalin-treated roots were as well aligned as in controls; however, the mean alignment direction, while consistently transverse in the controls, was increasingly variable with oryzalin concentration, meaning that microfibril orientation in one location tended to differ from that of a neighboring location. This conclusion was confirmed by direct observations of microfibrils with field-emission scanning electron microscopy. Taken together, these results suggest that cortical microtubules ensure microfibrils are aligned consistently across the organ, thereby endowing the organ with a uniform mechanical structure.
1 This work was supported by the U.S. Department of Energy (grant no. 03ER15421 to T.I.B.), which does not constitute endorsement by that department of views expressed herein. G.T.S.B. was supported by a University of Missouri Molecular Biology Program Postdoctoral Fellowship.
2 Present address: Biology Department, University of Massachusetts, Amherst, MA 01003.
3 Present address: Department of Plant Systems Biology, Flanders Interuniversity Institute for Biotechnology (VIB), Ghent University, Technologiepark 927, B–9052 Ghent, Belgium.
Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.104.040493.
* Corresponding author; e-mail baskin{at}bio.umass.edu; fax 413–545–3243.
Received February 4, 2004;
returned for revision May 24, 2004;
accepted June 13, 2004.
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