The cell wall is an extracellular structure that encloses each cell in land plants, algae, and fungi. It is more rigid and thicker than the extracellular matrix produced by animal cells, and is conventionally a prime point of differentiation between plants and animals. Typical cell walls in land plants are composed predominantly of polysaccharides, mainly cellulose microfibrils, which are embedded in a matrix of pectin and hemicellulose. Cellulose is synthesized by the cellulose-synthesizing complex localized on the plasma membrane. In contrast, hemicelluloses and pectins are synthesized in Golgi bodies, and carried to the plasma membrane by vesicles. Since cell walls connect cells to form tissues and provide tissues with mechanical strength, they determine the growth and development of the entire plant body. In addition, the cell wall works as an external sensor in responding to environmental stresses. The cell wall encloses each cell while at the same time enabling the transfer of solutes and signaling between cells via plasmodesmata, open channels in the cell wall. Casparian strips in the endodermis of vascular plant roots act as a barrier that is thought to be crucial for selective nutrient uptake and exclusion of pathogens. The process of cell wall formation can be more easily observed and analyzed in algae and fungi than in land plants. Unicellular algae demonstrate a variety of shapes, which are determined by their primary cell walls according to the specialized accumulation of cell wall materials. The nine figures selected for this chapter illustrate various aspects of cell walls in fungi, algae, and plants.
KeywordsCell Wall Secondary Cell Wall Cellulose Microfibril Primary Cell Wall Cell Wall Formation
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