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Measuring the mechanical properties of plant cells by combining micro-indentation with osmotic treatments.


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Authors

Weber, Alain 
Braybrook, Siobhan 
Huflejt, Michal 
Mosca, Gabriella 
Routier-Kierzkowska, Anne-Lise 

Abstract

Growth in plants results from the interaction between genetic and signalling networks and the mechanical properties of cells and tissues. There has been a recent resurgence in research directed at understanding the mechanical aspects of growth, and their feedback on genetic regulation. This has been driven in part by the development of new micro-indentation techniques to measure the mechanical properties of plant cells in vivo. However, the interpretation of indentation experiments remains a challenge, since the force measures results from a combination of turgor pressure, cell wall stiffness, and cell and indenter geometry. In order to interpret the measurements, an accurate mechanical model of the experiment is required. Here, we used a plant cell system with a simple geometry, Nicotiana tabacum Bright Yellow-2 (BY-2) cells, to examine the sensitivity of micro-indentation to a variety of mechanical and experimental parameters. Using a finite-element mechanical model, we found that, for indentations of a few microns on turgid cells, the measurements were mostly sensitive to turgor pressure and the radius of the cell, and not to the exact indenter shape or elastic properties of the cell wall. By complementing indentation experiments with osmotic experiments to measure the elastic strain in turgid cells, we could fit the model to both turgor pressure and cell wall elasticity. This allowed us to interpret apparent stiffness values in terms of meaningful physical parameters that are relevant for morphogenesis.

Description

This is the final version. It was first published by OUP at http://jxb.oxfordjournals.org/content/early/2015/04/07/jxb.erv135.abstract.

Keywords

BY-2, cell wall elasticity, cellular force microscopy, finite-element method, mechanical modelling, micro-indentation, osmotic treatments, sensitivity analysis, turgor pressure., Cell Wall, Elasticity, Microscopy, Atomic Force, Models, Theoretical, Osmotic Pressure, Plant Cells, Stress, Mechanical, Nicotiana

Journal Title

J Exp Bot

Conference Name

Journal ISSN

0022-0957
1460-2431

Volume Title

66

Publisher

Oxford University Press (OUP)
Sponsorship
This work was supported by SystemsX.ch, the Swiss National Science Foundation, the United States National Science Foundation International Research Fellowship (Award No. OISE-0853105) to SB, the University of Bern, and the Max Planck Institute for Plant Breeding Research in Cologne. We would like to thank A. Boudaoud, D. Vella, A. Ajdari, and A. Vaziri for discussing results and for helping us to compare our model with theirs. Furthermore, we would like to thank D. Felekis for helping us to validate our workflow on the SI-traceable stiffness standard, P. Barbier de Reuille for helping to improve the code for curve fitting, and U. Feller, S. Robinson, and C. Kuhlemeier for discussions.