Measurements of Wall Stress Relaxation in Growing Plant Cells

This chapter describes the pressure-block technique for stress relaxation in vivo. The method requires some specialized equipment but is currently the most informative and most useful method for analyzing the wall yielding properties that govern plant cell growth. Once the apparatus is set up, this method is easy to use and is suitable for measurements on a range of multicellular organs. The pressure-block technique is readily applied to intact plants, which means that it can be used to study many growth responses that are lost or attenuated on excision of the growing tissue. It provides the most reliable assessment of the yielding properties of the growing cell wall. To measure wall stress relaxation in growing cells, water uptake needs to be prevented. Then wall loosening results in a measurable decrease in wall stress and turgor pressure, rather than an increase in size. In the pressure-block technique, the growing part of the plant is sealed into a pressure chamber and growth is monitored at high temporal resolution, typically with an electronic position transducer attached to the plant inside the chamber. Stress relaxation is started by applying the minimum pressure needed to stop the plant from growing.