Minisymposium 5: Cell Walls

Abs # 15003: Mechanical properties of cell wall molecules

Presenter:	McCann, Maureen C, mmccann@bilbo.bio.purdue.edu
Authors	McCann, Maureen C (A)   Sugimoto, Keiko  (B)   Dahiya, Preeti  (B)   Ryden, Peter  (C)   Smith, Andrew  (C)   Bush, Max  (B)   Ulvskov, Peter  (D)   Vincken, Jean-Paul  (E)   Visser, Richard  (E)   Deryshire, Paul  (B)   Roberts, Keith  (B)
Affiliations:	(A): Purdue University (B): John Innes Centre (C): Institute of Food Research (D): University of Copenhagen (E): Wageniningen Agricultural University

Features of cell wall architecture which will influence mechanical properties, and therefore the ability of cells to expand, include the length and stiffness of the component fibers, their entanglement and physical interactions, the extent and nature of the cross-links, the hydrogen bonds and ionic interactions between polymers, 3-dimensional architecture and the water potential. Tissue architecture (cell shape and orientation) and overall anatomy (distribution of vascular bundles and fibers) also play major roles in determining mechanical properties of plant organs. We have developed a method to measure the mechanical properties of turgid or plasmolysed dark-grown Arabidopsis hypocotyls and assayed a range of mutants with genetically-defined variation in cell wall composition and architecture. From studies of the mur1, mur2 and mur3 mutants, we conclude that both galactosylated xyloglucan and rhamnogalacturonan II-borate di-di-ester cross-links are load-bearing in cell walls. The hyp 6 and hyp7 mutants have cellulose content similar to wild-type and normal tensile strength, but have altered matrix polysaccharide composition and decreased tensile moduli. Mutation in an arabinogalactan-like protein, that is a component of xylem cell walls, results in a brittle phenotype. We have two other indirect lines of evidence that pectins are likely to be involved in the control of cell expansion through their load-bearing mechanical properties within the wall. First, in collaboration with partner laboratories in an EU-funded network programme, we have shown that transgenic potato (Solanum tuberosum L.) plants expressing rhamnogalacturonan lyase targeted to the apoplast make tubers with clear morphological alterations, including radial swelling of cortical and periderm cells. This indicates that the substrate for the enzyme, intact rhamnogalacturonan I, is required to resist expansion forces in some cell types in potato. Second, by looking at many dwarf hypocotyl mutants of Arabidopsis, we have established strong correlative evidence that the degree of pectin esterification is limiting for cell elongation. Insertion mutants in pectin esterases that are expressed in hypocotyls grow taller than wild-type under particular growth conditions. In conclusion, we are beginning to dissect out the mechanical functions of specific cell wall polymers and their modifications by taking advantage of genetically-defined variation in cell wall composition and architecture.