Developments in the chemistry and biochemistry of pectic and hemicellulosic polymers.

Improved methods of isolation and analysis of cell walls from a range of plant tissues have shed new light on the structure of the constituent polymers, and have also helped to clarify some of the conflicting opinions on their mode of occurrence and association within the walls. The chemistry (and biochemistry) of pectic and hemicellulosic polymers in different types of plant organs is outlined, with particular emphasis on parenchymatous and immature tissues. The following aspects are discussed: the mode of occurrence of arabinans, galactans and arabinogalactans, and the possible association of some of them with proteins; the structural features of the esterified rhamnogalacturonans and associated neutral sugar residues in the pectic substances of middle lamellae and primary cell walls; the occurrence of acidic xylans, acidic arabinoxylans, and acidic arabinoxylans in association with other polymers in the cell walls of cambial, suspension-cultured and parenchymatous tissues of dicotyledons; evidence for the occurrence of small but significant amounts of xyloglucans in association with other polymers, and the occurrence of a range of xyloglucans in parenchymatous tissues; evidence for the occurrence of phenolic ester and phenolic cross-linkages between the cell wall polymers of parenchymatous tissues of both dicotyledons and monocotyledons, particularly the association of hydroxycinnamic acids with some pectic substances; the occurrence of proteoglycans and proteoglycan-polyphenol complexes and their relationship to the traditional hemicelluloses; and some aspects of the non-cellulosic polymers of non-endospermic and endospermic seeds.