Measuring plant cell wall creep and expansin activity with a commercial texture analyzer

Abstract

Plant growth comprises an irreversible extension of preexistent cell wall. This extension is mediated by phyto-hormones (majorly auxins and giberellins) and by light. Also, cell wall experiments a transient extension when under tension at acidic pH. This extension would not be mediated by cell wall synthetic processes. Cosgrove (1989) analyzed the cell wall creep in cucumber (Cucumis sativus) hypocotyls and showed its behavior under different treatments, concluding that the hypocotyl creep is an enzyme dependent process. In 1992, McQueen Mason et al. proved that this creep activity is indeed mediated by non-hydrolytic enzymes called “expansins”. To the moment, expansin activity measurement requires “ad hoc” instrument construction, which has considerably limited this study to a few laboratories. The objective of this work was to adapt the Texture Analyser TA.XT plus in order to develop a measuring system for cell wall creep and expansin activity. In order to demonstrate cell wall creep and optimize the methodology, pH shifting assays were performed. The influence of different chemicals agents was also assayed. Expansin activity was determined in a reconstitution of the cell wall creep assay, using a thermally denatured cucumber hypocotyl and a total cucumber hypocotyl protein extract. This optimized methodology will allow analyzing both parameters in a broad variety of vegetables tissues.