Cellular force microscopy for in vivo Measurements of plant tissue mechanics

Although growth and morphogenesis are controlled by genetics, physical shape change in plant tissue results from a balance between cell wall loosening and intracellular pressure. Despite recent work demonstrating a role for mechanical signals in morphogenesis, precise measurement of mechanical properties at the individual cell level remains a technical challenge. To address this challenge we have developed Cellular Force Microscopy (CFM) that combines the versatility of classical micro-indentation techniques with high automation and resolution approaching that of atomic force microscopy. CFM's large range of forces provides the possibility to map the apparent stiffness of both plasmolysed and turgid tissue, as well as perform micro-puncture of cells using very high stresses. CFM experiments reveal that, within a tissue, local stiffness measurements can vary with the level of turgor pressure in an unexpected way. Altogether, our results highlight the importance of detailed physically based simulations for the interpretation of micro-indentation results. CFM's ability to be used both to assess and manipulate tissue mechanics makes it a method of choice to unravel the feedbacks between mechanics, genetics and morphogenesis