Cell Wall Polysaccharide Composition and Covalent Crosslinking

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 modifi cations 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 [microfi brillar β -(1 → 4) -d -glucan], pectins ( α -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 α -xylo -β -glucans, β -xylans (including α -arabino -β -xylans, α -glucurono -β -xylans, etc.) and β -mannans (including α -galacto -β -mannans, β -gluco -β -mannans, etc.). Another hemicellulose [mixed -linkage β -(1 → 3)(1 → 4) -d -glucan) is confi ned 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.

Effect of water deficit on the cell wall of the date palm (Phoenix dactylifera ‘Deglet nour’, Arecales) fruit during development

“…But instead, it may originate from cellulose and/or XyG degradation, or from the water soluble (1→3,1→4)-mixed-linkage glucan found in the pulp of mature fruits of P. dactylifera var. Nakhla (Ishurd et al 2002).To date, mixed-linkage glucan has been confirmed to occur in members of the Poales (Fry 2011) and in Equisetum (Fry et al 2008) and was shown to appear transiently depending on the developmental stages. It has not been found in other land plants.…”

“…The cell wall of land plant consists mainly of polysaccharides including pectins, hemicellulose and cellulose with structural glycoproteins and enzymes (Popper et al 2011). Pectins are complex wall polymers consisting of homogalacturonan (HG) that can be methyl-and acetyl-esterified, rhamnogalacturonan I (RG-I), rhamnogalacturonan II (RG-II) and xylogalacturonan (Fry 2011). HG is a polymer of repeated units of (1→4)-a-D-galacturonic acid (GalA) that can be cross-linked with calcium upon block-wise action of pectin methylesterases on methylesterified HG (Micheli 2001).…”

Phylogenetic variation in glycosidases and glycanases acting on plant cell wall polysaccharides, and the detection of transglycosidase and trans‐β‐xylanase activities

“…The restriction of appreciable MXE activity, among land plants, to the single genus Equisetum also emphasises the phylogenetic differences in wall metabolism between plant taxa. This view is reinforced by the emerging realisation that land plants exhibit major taxonomic differences in their wall polysaccharide chemistry: many of the landmark steps in plant evolution were accompanied by remarkable changes in the chemistry of the primary cell wall (Popper, 2008;Sørensen et al, 2010;Fry, 2011), which must have necessitated changes in the wall enzyme profile. For example: only the Poales and Equisetales possess MLG (Trethewey et al, 2005;Fry et al, 2008b); only land plants (not their sister group the Charophyta) have xyloglucan as a major wall component in the vegetative tissues Domozych et al, 2009); the Poales and the Solanales have low-fucose xyloglucan (Carpita and Gibeaut, 1993;McDougall and Fry, 1994;Hoffman et al, 2005); mosses and liverworts uniquely have xyloglucans rich in b-D-galacturonic acid (Peñ a et al, 2008); Equisetum and Selaginella have xyloglucan containing a-L-arabinopyranose in place of many of the b-D-galactopyranose residues (Peñ a et al, 2008); Anthoceros, a hornwort, has polysaccharides uniquely rich in a-D-glucuronosyl-(1fi3)-L-galactose units ; lycopodiophytes (the earliest-diverging vascular plants) share an unusual abundance of 3-O-methyl-D-galactose residues (Popper et al, 2001); walls of charophytes, bryophytes and homosporous lycopodiophytes are rich in 3-O-methylrhamnose, which is undetectable in other land plants ; and the eusporangiate fi leptosporangiate transition among fern-allies was accompanied by a marked decrease in mannan content .…”

Trans‐α‐xylosidase and trans‐β‐galactosidase activities, widespread in plants, modify and stabilize xyloglucan structures

“…Xyloglucan is the major hemicellulose in primary cell walls of most land plants (Albersheim et al, 2010;Fry, 2011a). It hydrogen bonds to microfibril surfaces, coating them as a monolayer.…”