Mechanical Measurements on Living Plant Cells by Micro- indentation with Cellular Force Microscopy - Plant Cell Morphogenesis: Methods and Protocols - page 131

Chapter 11

Mechanical Measurements on Living Plant Cells
by Micro-indentation with Cellular Force Microscopy

Anne-Lise Routier-Kierzkowska and Richard S. Smith

Abstract

Indentation methods on the micro- and nanoscale are increasingly used to assess mechanical properties of
living plant tissues. These techniques rely on recording the force resulting from indenting the cell surface
with a small probe. Depending on the scale of indentation and the indenter shape, force-indentation data
will refl ect several factors such as cell wall elasticity, turgor pressure, cell and tip geometry, and contact
angle. Cellular force microscopy is a micro-indentation method that was designed to precisely measure and
apply forces on living plant cells. Here we explain how to use this method to map the apparent stiffness in
single cells and tissues.

Key words Plant mechanics, Micro-indentation, Turgor pressure, Primary cell wall, Elastic modulus,
Stiffness, Mechanosensing

1 Introduction

The variety of plant cell shape and growth patterns can be attrib-
uted to two primary factors, turgor pressure and cell wall mechani-
cal properties. The cell walls, which are only a few hundred
nanometers thick, support large tensile stresses (100-1,000 atm)
created by the high internal turgor pressure, typically 3-10 atm
[ 1 ]. Different methods have been used to measure mechanical
properties of the primary cell wall and turgor pressure [ 2 , 3 ].
Indentation methods can be used to measure cellular mechanical
properties by deforming the cell surface with an indenter while
monitoring both force and tip displacement. These methods are
used at various scales, either deforming the whole cell with a large
probe or indenting the cell wall very locally with a sharp needle.
Compression of whole cells is used to evaluate turgor pressure as
well as cell wall elasticity and wall strength, i.e., the force needed to
rupture it [ 4 - 8 ]. Nano-indentation experiments, on the other
hand, rely on very localized indentation of the cell wall with the
sharp tip of an atomic force microscope (AFM) to deduce wall