tailieunhanh - Plant physiology - Chapter 15 Cell Walls: Structure, Biogenesis, and Expansion

PLANT CELLS, UNLIKE ANIMAL CELLS, are surrounded by a relatively thin but mechanically strong cell wall. This wall consists of a complex mixture of polysaccharides and other polymers that are secreted by the cell and are assembled into an organized network linked together by both covalent and noncovalent bonds. Plant cell walls also contain structural proteins, enzymes, phenolic polymers, and other materials that modify the wall’s physical and chemical characteristics. The cell walls of prokaryotes, fungi, algae, and plants are distinctive from each other in chemical composition and microscopic structure, yet they all serve two common primary functions: regulating cell. | Chapter 15 Cell Walls Structure Biogenesis and Expansion PLANT CELLS UNLIKE ANIMAL CELLS are surrounded by a relatively thin but mechanically strong cell wall. This wall consists of a complex mixture of polysaccharides and other polymers that are secreted by the cell and are assembled into an organized network linked together by both covalent and noncovalent bonds. Plant cell walls also contain structural proteins enzymes phenolic polymers and other materials that modify the wall s physical and chemical characteristics. The cell walls of prokaryotes fungi algae and plants are distinctive from each other in chemical composition and microscopic structure yet they all serve two common primary functions regulating cell volume and determining cell shape. As we will see however plant cell walls have acquired additional functions that are not apparent in the walls of other organisms. Because of these diverse functions the structure and composition of plant cell walls are complex and variable. In addition to these biological functions the plant cell wall is important in human economics. As a natural product the plant cell wall is used commercially in the form of paper textiles fibers cotton flax hemp and others charcoal lumber and other wood products. Another major use of plant cell walls is in the form of extracted polysaccharides that have been modified to make plastics films coatings adhesives gels and thickeners in a huge variety of products. As the most abundant reservoir of organic carbon in nature the plant cell wall also takes part in the processes of carbon flow through ecosystems. The organic substances that make up humus in the soil and that enhance soil structure and fertility are derived from cell walls. Finally as an important source of roughage in our diet the plant cell wall is a significant factor in human health and nutrition. We begin this chapter with a description of the general structure and composition of cell walls and the mechanisms of the .