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Columella cells revisited: novel structures, novel properties, and a novel gravisensing modelA hundred years of research has not produced a clear understanding of the mechanism that transduces the energy associated with the sedimentation of starch-filled amyloplast statoliths in root cap columella cells into a growth response. Most models postulate that the statoliths interact with microfilaments (MF) to transmit signals to the plasma membrane (or ER), or that sedimentation onto these organelles produces the signals. However, no direct evidence for statolith-MF links has been reported, and no asymmetric structures of columella cells have been identified that might explain how a root turned by 90 degrees knows which side is up. To address these and other questions, we have (1) quantitatively examined the effects of microgravity on the size, number, and spatial distribution of statoliths; (2) re-evaluated the ultrastructure of columella cells in high-pressure frozen/freeze-substituted roots; and (3) followed the sedimentation dynamics of statolith movements in reoriented root tips. The findings have led to the formulation of a new model for the gravity-sensing apparatus of roots, which envisages the cytoplasm pervaded by an actin-based cytoskeletal network. This network is denser in the ER-devoid central region of the cell than in the ER-rich cell cortex and is coupled to receptors in the plasma membrane. Statolith sedimentation is postulated to disrupt the network and its links to receptors in some regions of the cell cortex, while allowing them to reform in other regions and thereby produce a directional signal.
Document ID
20040088889
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
Authors
Staehelin, L. A.
(University of Colorado Boulder, United States)
Zheng, H. Q.
Yoder, T. L.
Smith, J. D.
Todd, P.
Date Acquired
August 21, 2013
Publication Date
June 1, 2000
Publication Information
Publication: Gravitational and space biology bulletin : publication of the American Society for Gravitational and Space Biology
Volume: 13
Issue: 2
ISSN: 1089-988X
Subject Category
Life Sciences (General)
Funding Number(s)
CONTRACT_GRANT: NAG5-3967
CONTRACT_GRANT: NCC8-131
Distribution Limits
Public
Copyright
Other
Keywords
NASA Discipline Cell Biology
Non-NASA Center

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