Primary galactoglucomannans

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]. 

Figure 3.4 Structures of the galactoglucomannan (a heteromannan) known to occur in the primary cell walls of several species of eudicotyledons and the glucuronoarabinoxylan (a heteroxylan) known to occur in the primary cell walls of sycamore (Acer pseudoplatanus). The structures of the heteromannans and heteroxylans in potato cell walls are unknown.

The whole pectin fraction usually contains one or both types of pectinic acid and arabinogalactans. Hemicellulose is a complex mixture of arabino-galactan, xylans, sometimes some glucomannan or galactoglucomannan, and callose. Its composition is variable with the source. The cellulose fraction, not only contains p-l,4-glucan, but almost always has small amounts of inseparable glucomannan. The primary cell wall is relatively richer in hemicellulose than the secondary wall, while the latter contains a good deal of cellulose. Pectins are found in primary walls and probably comprise much of the middle lamella. 

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