Document Detail

Cell wall extension results in the coordinate separation of parallel microfibrils: evidence from scanning electron microscopy and atomic force microscopy.
MedLine Citation:
PMID:  15998305     Owner:  NLM     Status:  MEDLINE    
Enlargement of the cell wall requires separation of cellulose microfibrils, mediated by proteins such as expansin; according to the multi-net growth hypothesis, enlargement passively reorients microfibrils. However, at the molecular scale, little is known about the specific movement of microfibrils. To find out, we examined directly changes in microfibril orientation when walls were extended slowly in vitro under constant load (creep). Frozen-thawed cucumber hypocotyl segments were strained by 20-30% by incubation in pH 4.5 buffer or by incubation of heat-inactivated segments in alpha-expansin or a fungal endoglucanase (Cel12A). Subsequently, the innermost layer of the cell wall was imaged, with neither extraction nor homogenization, by field-emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). AFM images revealed that sample preparation for FESEM did not appreciably alter cell wall ultrastructure. In both FESEM and AFM, images from extended and non-extended samples appeared indistinguishable. To quantify orientational order, we used a novel algorithm to characterize the fast Fourier transform of the image as a function of spatial frequency. For both FESEM and AFM images, the transforms of non-extended samples were indistinguishable from those of samples extended by alpha-expansin or Cel12A, as were AFM images of samples extended by acidic buffer. We conclude that cell walls in vitro can extend slowly by a creep mechanism without passive reorientation of innermost microfibrils, implying that wall loosening agents act selectively on the cross-linking polymers between parallel microfibrils, rather than more generally on the wall matrix.
Francoise Marga; Michel Grandbois; Daniel J Cosgrove; Tobias I Baskin
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Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, Non-P.H.S.    
Journal Detail:
Title:  The Plant journal : for cell and molecular biology     Volume:  43     ISSN:  0960-7412     ISO Abbreviation:  Plant J.     Publication Date:  2005 Jul 
Date Detail:
Created Date:  2005-07-06     Completed Date:  2005-09-12     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  9207397     Medline TA:  Plant J     Country:  England    
Other Details:
Languages:  eng     Pagination:  181-90     Citation Subset:  IM    
Division of Biological Sciences, University of Missouri, 109 Tucker Hall, Columbia, MO 65211, USA.
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MeSH Terms
Cell Wall / physiology*,  ultrastructure
Cucumis sativus / physiology*
Microfibrils / physiology*
Microscopy, Atomic Force
Microscopy, Electron, Scanning

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