Cellulose is an abundant biopolymer that is synthesized by all plants, most algae, a number of bacteria including cyanobacteria, the cellular slime mold, and the ascidians (a group of animals) (Brown, 1996). The major proportion of cellulose, produced in the biosphere by plants, adds strength to the plant cell wall and helps in determining the direction of cell and plant growth. The plant cell wall itself is a complex of polysaccharides, which include cellulose and noncellulosic polysaccharides (hemicelluloses and pectins), as well as lignins and proteins. All plant cells have a primary cell wall consisting of cellulose, hemicellulose, pectin, and proteins; however, some cells additionally have a secondary cell wall consisting mainly of cellulose and lignins, and it is in these cells that the proportion of cellulose is increased considerably. The importance of cellulose as an essential component of plants and its uses in our daily lives cannot be overemphasized. Interestingly, cellulose also is the most important industrial polysaccharide, and considering its unique physical properties, it has been studied widely by chemists since its initial discovery by Anselme Payen almost 165 years ago (Klemm et al., 2005).

Studies on the structure of cellulose have been crucial in developing concepts regarding the sites of cellulose synthesis and the mechanism by which it is synthesized (Preston, 1974). Although much more is known about the structure of cellulose (and these studies are still continuing) (Nishiyama et al., 2003), the last decade and a half has witnessed a surge in our understanding of the biosynthesis of cellulose in plants. Many of these advances are related to the identification of genes for cellulose biosynthesis in plants (Arioli et al., 1998; Pear et al., 1996), analysis of mutants affected in cellulose biosynthesis (Robert et al., 2004), the capability to analyze cellulose synthesis in vitro using cell-free extracts (Kudlicka and Brown, 1997; Lai-Kee-Him et al., 2002), and visualization of enzymes involved in cellulose synthesis in living plant cells (Paredez et al., 2006; Robert et al., 2005). In this chapter, we will discuss the development of present-day concepts related to cellulose biosynthesis and the prospects of modifying this property in plants.