Structural Polysaccharides In Molecular Architecture of Plant Cell Wallsfrom Algae to Hardwoods
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STRUCTURAL POLYSACCHARIDES IN MOLECULAR ARCHITECTURE OF PLANT CELL WALLSFROM ALGAE TO HARDWOODS R.H. ATALLA AND J.M. HACKNEY USDA Forest Service, Forest Products Laboratory, One Gifford Pinchot Drive, Madison, WI 53705-2398
ABSTRACT The structural polysaccharides are a family of polymers of hexoses and pentoses that occur in all plant cell walls. The distinguishing characteristic of these polymers is a /3-1,4-linked backbone. The most common among these is cellulose, which is the linear homopolymer of anhydroglucose. These polysaccharides are capable of aggregating into highly ordered structures that are the primary determinants of the mechanical and physical properties of cell walls. An overview of the variations in patterns. of structural-polysaccharide aggregation within cell walls is presented here. Among the majority of the algae cellulose is the dominant structural polysaccharide; thus the habit of aggregation is dominated by the patterns of cellulose. Among primitive plants, other structural polysaccharides represent a larger fraction of cell-wall mass and cellulose is less dominant. In woody tissues of higher plants, structural polysaccharides are the major components of the cell wall, and the patterns of aggregation are again dominated by the characteristic habits of cellulose. Within tile phylogenetic framework, higher levels of morphological development apparently involve greater complexity in the molecular architecture of the cell walls and a finer level of blending of the components of aggregates at the molecular level.
INTRODUCTION The primary structural components of plant cell walls are a group of polymers with backbones made up of /3-1,4-linked monosaccharides. The dominant polymer is, in most instances, cellulose; it is the homopolymer of anhydroglucose shown here schematically.
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The manner of coaggregation of cellulose with other cell-wall constituents varies widely. In material terms, the different forms of coaggregation include composite structures in which the cellulosic component can be viewed as a separate phase embedded in a matrix of other constituents, genuine blends wherein the mixing of the constituents is at the molecular level, and more complex architectures that are intermediate between, or combinations of, these two forms of organization. We recently began a survey of this range of variation and its relationship to the phylogeny of source species from various divisions of photosynthetic organisms. We provide here an overview of these findings and discuss levels of
Mat. Res. Soc. Symp. Proc. Vol. 255. @1992 Materials Research Society
388
organizational complexity at the molecular level as they relate to the morphological complexity of organisms within the evolutionary scheme of the plant kingdom. To establish an appropriate perspective, we begin by discussing variation in patterns of cellulose aggregation when it occurs either in pure form in the native state or in a form that allow
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