title: Measuring the mechanical properties of plant cells by combining micro-indentation with osmotic treatments.
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.
authors: Institute of Plant Sciences, University of Bern, Altenbergrain 21, CH-3013 Bern, Switzerland.
authors: Alain
authors: A
authors: Weber
authors: Institute of Plant Sciences, University of Bern, Altenbergrain 21, CH-3013 Bern, Switzerland Sainsbury Laboratory, Bateman Street, Cambridge, CB2 1LR, UK.
authors: Siobhan
authors: S
authors: Braybrook
authors: Institute of Plant Sciences, University of Bern, Altenbergrain 21, CH-3013 Bern, Switzerland.
authors: Michal
authors: M
authors: Huflejt
authors: Institute of Plant Sciences, University of Bern, Altenbergrain 21, CH-3013 Bern, Switzerland Max Planck Institute for Plant Breeding Research, Carl-von-Linné-Weg 1050829 Köln, Cologne, Germany.
authors: Gabriella
authors: G
authors: Mosca
authors: Institute of Plant Sciences, University of Bern, Altenbergrain 21, CH-3013 Bern, Switzerland Max Planck Institute for Plant Breeding Research, Carl-von-Linné-Weg 1050829 Köln, Cologne, Germany.
authors: Anne-Lise
authors: AL
authors: Routier-Kierzkowska
authors: Institute of Plant Sciences, University of Bern, Altenbergrain 21, CH-3013 Bern, Switzerland Max Planck Institute for Plant Breeding Research, Carl-von-Linné-Weg 1050829 Köln, Cologne, Germany smith@mpipz.mpg.de.
authors: Richard S
authors: RS
authors: Smith
mesh_terms: D002473:Cell Wall / Q000502:physiology*; D004548:Elasticity; D018625:Microscopy, Atomic Force; D008962:Models, Theoretical; D009997:Osmotic Pressure; D059828:Plant Cells / Q000502:physiology*; D013314:Stress, Mechanical; D014026:Nicotiana / Q000254:growth & development / Q000502:physiology*
keywords: BY-2; cell wall elasticity; cellular force microscopy; finite-element method; mechanical modelling; micro-indentation; osmotic treatments; sensitivity analysis; turgor pressure.