The Primary Cell Walls of Higher Plants

Glucomannans (GM) and galactoglucomannans (GGM), common constituents of plant cell walls, are the major hemicellulosic components of the secondary cell walls of softwoods, whereas in the secondary cell walls of hardwoods they occur in minor amounts. They are suggested to be present together with xylan and fucogalactoxyloglucan in the primary cell walls of higher plants [192]. These polysaccharides were extensively studied in the 1960s [6,193]. 

Rhamnogalacturonan 11 (RG-11) is a structurally complex, pectic polysaccharide that is present in the primary cell-walls of higher plants. It is composed of 60 glycosyl residues, and is a very complex molecule indeed. For example, on acid hydrolysis, at least ten different monosaccharides are formed, including the novel aceric acid (30), which is the only branched-... 

Pectic substances are important structural components of the middle lamellea and the primary cell walls of higher plants, in particular fruits and vegetables. The extent and mode of their degradation by enzymes affect many aspects of the processing of fruits and vegetables and many quality attributes of fruit and vegetable products. 

Albersheim P, Darvill AG, O Neill MA, Schols HA, Voragen AGJ (1996) An hypothesis the same six polysaccharides are components of the primary cell walls of higher plants. In Visser J, Voragen AGJ (eds) Pectins and pectinases. Elsevier, Amsterdam, pp 47-55... 

This essay was written in an attempt to explain our overview of primary cell walls and to reach consensus on the nomenclature of primary cell wall polysaccharides. We present evidence supporting the hypothesis that cellulose, xyloglucan, arabinoxylan, homogalacturonan, RG-I, and RG-II are the six polysaccharides common to all primary cell walls of higher plants. In many cells, these six polysaccharides account for all or nearly all of the primary wall polysaccharides. Like the physically interacting proteins that constitute the electron transport machinery of mitochondria, the structures of the six patently ubiquitous polysaccharides of primary cell walls have been conserved during evolution. Indeed, we hypothesize that the common set of six structural polysaccharides of primary cell walls have been structurally... 

The primary cell walls of most higher plant species contain XGs of the XXXG type, which bear trisaccharide side chains (8) on the backbone [247]. The seeds of many plants contain XXXG-type XGs, in which about 30% of the xylose units possess a /3-D-Galp residue attached to position 2. Several plant species produce XGs that lack fucose and galactose, and have a-L-Ara/ attached to 0-2 of some of the Xylp side-chains, such as XG isolated from olive fruit [262] and soybean (Glycine maxima) meal [263]. However, a-L-Ara/ residues occur also 2-linked directly to some of the Glcp residues of the backbone [154]. 

An Hypothesis The Same Six Polysaccharides are Components of the Primary Cell Walls of All Higher Plants... 

In the cell walls of higher plants,178 hemicelluloses are found in close association with cellulose and lignin, and evidence for the distribution of these three main components in the various parts of the wall has been obtained by staining techniques.179 It is not certain, however, whether the close association of these substances can be accounted for entirely in terms of physical entanglement and secondary forces (van der Waals and hydrogen bonding) or whether primary chemical bonds unite some of the components. 

Differences in compositions of the cell walls of higher plants occur within phyla, classes, families, and genera of higher plants, with location within a given plant (because different cells have different functions and exist in different environments), and with stage of development [15]. Nevertheless, some general features can be described. Polysaccharides are the primary constituents of plant cell walls. 

We hypothesize that the fundamental processes of cell wall expansion are conserved in all higher plants, that is, growth of the cells of all higher plants requires the synthesis and insertion of the same polysaccharides by the same procedures. If this hypothesis is correct, then all primary cell walls have a common set of stmctural polysaccharides. The commonality of the primary cell wall polysaccharides hypothesis does not require that (i) the common polysaccharides be present in all cell walls in the same proportions, (ii) the polysaccharides be... 

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