Introduction
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.