title: The pollen tube: a soft shell with a hard core.
abstract: Plant cell expansion is controlled by a fine-tuned balance between intracellular turgor pressure, cell wall loosening and cell wall biosynthesis. To understand these processes, it is important to gain in-depth knowledge of cell wall mechanics. Pollen tubes are tip-growing cells that provide an ideal system to study mechanical properties at the single cell level. With the available approaches it was not easy to measure important mechanical parameters of pollen tubes, such as the elasticity of the cell wall. We used a cellular force microscope (CFM) to measure the apparent stiffness of lily pollen tubes. In combination with a mechanical model based on the finite element method (FEM), this allowed us to calculate turgor pressure and cell wall elasticity, which we found to be around 0.3 MPa and 20-90 MPa, respectively. Furthermore, and in contrast to previous reports, we showed that the difference in stiffness between the pollen tube tip and the shank can be explained solely by the geometry of the pollen tube. CFM, in combination with an FEM-based model, provides a powerful method to evaluate important mechanical parameters of single, growing cells. Our findings indicate that the cell wall of growing pollen tubes has mechanical properties similar to rubber. This suggests that a fully turgid pollen tube is a relatively stiff, yet flexible cell that can react very quickly to obstacles or attractants by adjusting the direction of growth on its way through the female transmitting tissue.
authors.affiliation: Institute of Plant Biology and Zürich-Basel Plant Science Center, University of Zürich, Zollikerstrasse 107, CH 8008, Zürich, Switzerland.
authors.forename: Hannes
authors.initials: H
authors.lastname: Vogler
authors.forename: Christian
authors.initials: C
authors.lastname: Draeger
authors.forename: Alain
authors.initials: A
authors.lastname: Weber
authors.forename: Dimitris
authors.initials: D
authors.lastname: Felekis
authors.forename: Christof
authors.initials: C
authors.lastname: Eichenberger
authors.forename: Anne-Lise
authors.initials: AL
authors.lastname: Routier-Kierzkowska
authors.forename: Aurélien
authors.initials: A
authors.lastname: Boisson-Dernier
authors.forename: Christoph
authors.initials: C
authors.lastname: Ringli
authors.forename: Bradley J
authors.initials: BJ
authors.lastname: Nelson
authors.forename: Richard S
authors.initials: RS
authors.lastname: Smith
authors.forename: Ueli
authors.initials: U
authors.lastname: Grossniklaus
mesh_terms: D001696:Biomechanical Phenomena; D002473:Cell Wall / Q000502:physiology; D003198:Computer Simulation; D004548:Elasticity; D027762:Lilium / Q000033:anatomy & histology / Q000502:physiology*; D008853:Microscopy / Q000295:instrumentation / Q000379:methods; D008954:Models, Biological; D059828:Plant Cells / Q000502:physiology*; D053205:Pollen Tube / Q000033:anatomy & histology / Q000502:physiology*; D011312:Pressure; D013314:Stress, Mechanical