Plant cell-walls chemical composition

The plant cell wall is a composite of cellulose (the main fibre) plus shorter lengths (hemicellulose) that help bind the fibre, plus pectin (the main matrix adhesive) and some proteins. There are fruits that have a soft melting texture when ripe (e.g., avocado and blackberry) in which the cell wall swells noticeably. This swelling is related to the degree of solubilisation of the pectin (Redgwell et al. 1997) which can be removed in vitro using enzymes or other chemicals. 

A coherent discussion of the above topic should, therefore, include consideration of the relevant aspects of composition, structure, and evolution of the plant cell-walls development of present knowledge concerning the physicochemical properties of cellulosic microfibrils the biological processes that account for the production and properties of the wall materials and the cell organelles that are instrumental in the execution of these processes. The present article provides a brief review of these multidisciplinary subjects. The chemical and physical properties of the structural polysaccharides and their bio-syntheses, have been excellently reviewed in previous Volumes of this Series. Therefore, consideration of these subjects has, so far as possible, been avoided in favor of discussing development of our present knowledge through different approaches and diverse opinions. 

As plant cells grow, they deposit new layers of cellulose external to the plasma membrane by exocytosis. The newest regions, which are laid down successively in three layers next to the plasma membrane, are termed the secondary cell wall. Because the latter varies in its chemical composition and structure at different locations around the cell, Golgi-derived vesicles must be guided by the cytoskeleton... 

Grain legumes have also been processed into refined starch (10,11) and protein isolates (12,13,14) by procedures derived from the traditional corn starch and soybean protein industries (15). However, comparative data on product yields, composition and losses have not been published. A commercial plant for the wet processing of field pea into refined starch, protein isolate and refined fiber has been established in Western Canada. Little is known about the characteristics of the protein isolate or refined fiber product. Water-washed starch prepared from the air-classified starch fractions of field pea (16,17) and fababean (6) have been investigated for certain physico-chemical and pasting properties. Reichert (18) isolated the cell wall material from soaked field pea cotyledons and determined its fiber composition and water absorption capacity. In addition, the effects of drying techniques on the characteristics of pea protein Isolates have been determined (14). 

While for some plant species the cell wall composition has been studied, the actual three-dimensional organization of the polysaccharides in the cell wall has not been fully elucidated. Moreover, it appears that while some aspects are constant for all walls (i.e., the presence of similar types of polysaccharides), the relative proportion and fine structure of the polysaccharides may be different, and thus the way they are organized in the wall may be different. Determination of the composition of polysaccharides in cell walls is commonly done by chemical analytical methods, but prior to determining the composition or structure of the polysaccharides in cell walls, the walls must first be isolated from the plant tissues and separated from the intracellular material. 

Generalized representations of the internal structures of animal and plant cells (eukaryotic cells). Cells are the fundamental units in all living systems, and they vary tremendously in size and shape. All cells are functionally separated from their environment by the plasma membrane that encloses the cytoplasm. Plant cells have two structures not found in animal cells a cellulose cell wall, exterior to the plasma membrane, and chloroplasts. The many different types of bacteria (prokaryotes) are all smaller than most plant and animal cells. Bacteria, like plant cells, have an exterior cell wall, but it differs greatly in chemical composition and structure from the cell wall in plants. Like all other cells, bacteria have a plasma membrane that functionally separates them from their environment. Some bacteria also have a second membrane, the outer membrane, which is exterior to the cell wall. 

Wood chemicals are derived from woody plants made of strong, relatively thick-walled long cells that make good libers. The cell wall in this type of plant is a complex mixture of polymers that varies in composition. The solid portion of wood is over 95% organic material that is a mixture of three groups of polymers ... 

Most important are likely environmental factors associated with cultivation, crop management, and postharvest processes that can be controlled to some extent and on the other hand also have a large impact on the chemical composition, cell-wall architecture, or conversion processing behavior of plant biomass. These factors could form the basis of a testable strategy to decrease the variance associated with these characteristics. 

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