Cell Wall Polysaccharide Composition And Covalent Crosslinking

The Edinburgh Cell Wall Group, Institute of Molecular Plant Sciences, The University of Edinburgh, The King's Buildings, Edinburgh EH9 3JH, UK

Manuscript received February 2008

Abstract: Genetics now potentially lets us modify the production, crosslinking and degradation of cell wall polysaccharides. There remains, however, the need to test experimentally whether intended modifications of polysaccharide metabolism have successfully been effected in vivo. Simple methods for this are described, including in-vivo radiolabelling, enzymic dissection (e.g. with Driselase) and chromatographic/electrophoretic fractionation of dissection products.

After an overview of polysaccharide chemistry, I discuss the structures and taxonomic distribution of wall polysaccharides in charophytes and land plants. Primary and secondary walls are compared.

The major wall polysaccharides are cellulose [microfibrillar P-(1^4)-D-glucan], pectins (a-D-galacturonate-rich) and hemicelluloses (lacking galacturonate; hydrogen-bonding to cellulose; extractable by 6 M NaOH at 37 °C). Land-plant pectins are anionic polymers built of about four glycosidically interconnected domains (homogalacturonan, rhamnogalacturonans I and II, xylogalacturonan). Hemicelluloses occurring in most/all land plants are a-xylo-P-glucans, P-xylans (including a-arabino-P-xylans, a-glucurono-P-xylans, etc.) and P-mannans (including a-galacto-P-mannans, P-gluco-P-mannans, etc.). Another hemicellulose [mixed-linkage P-(1^3)(1^4)-D-glucan) is confined to Equisetum and some Poales.

Other taxonomically restricted features of angiosperm primary walls occur in Poales (xylose-poor xyloglucans; feruloylated arabinoxylans); Solanales and Lamiales (characteristic xyloglucans); Caryophyllales (feruloylated pectins); and Alismatales (apiogalacturonan). I also summarize characteristic wall features of charophytes, bryophytes, lycopodiophytes, fern-allies and gymnosperms.

Annual Plant Reviews Volume 41: Plant Polysaccharides, Biosynthesis and Bioengineering Edited by P. Ulvskov © 2011 Blackwell Publishing Ltd. ISBN: 978-1-405-18172-3

Stephen C. Fry

The making or breaking of a 'crosslink' (defined as an individual chemical bond, not a whole 'tethering' chain) may cause wall tightening/loosening. Covalent crosslinks include phenolic coupling products, uronoyl esters and amides, and borate diesters.

Keywords: angiosperms; apiogalacturonan; bryophytes; cellulose; charophytes; chromatography; crosslinks (covalent); Driselase; electrophoresis (paper); gymno-sperms; hemicellulose; homogalacturonan; hydrolysis; mannans; mixed-linkage glucans; pectins ; polysaccharide chemistry ; primary wall ; pteridophytes ; radio-labelling; rhamnogalacturonans ; secondary wall ; taxonomic variation ; uronoyl esters/amides; xylans ; xylogalacturonan ; xyloglucan

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