Some possible sources of error in determining bulk elastic moduli and other parameters from pressure–volume curves of shoots and leaves

Abstract

Pressure–volume curves were constructed from well defined models and hypothetical shoots in which reasonable values of osmotic pressure and cell wall elastic moduli were specified for cell types of different relative volumes. The pressure–volume curves so obtained closely resembled those of real shoots and leaves. Comparing the bulk parameters obtained from analysis of the constructed pressure–volume curves with the values defined in the models allows us to examine the sources of error in their evaluation. The graphical values of the original bulk osmotic pressure and of the total volume of osmotic (symplasmic) water agreed very well with those defined; however, the osmotic pressure at incipient plasmolysis and the bulk elastic moduli estimated from the graph were generally lower than their actual values originally used in the models. We show that the apparent linear dependence of the bulk elastic modulus of sitka spruce reported by Hellkvist et al. (1974) may not reflect a similar linearity for the elastic moduli of individual cells.