Carbon partitioning to cellulose synthesis

This article discusses the importance and implications of regulating carbon partitioning to cellulose synthesis, the characteristics of cells that ser ve as major sinks for cellulose deposition, and enzymes that participate in the conversion of supplied carbon to cellulose. Cotton fibers, which depos it almost pure cellulose into their secondary cell walls, are referred to a s a primary model system. For sucrose synthase, we discuss its proposed rol e in channeling UDP-Glc to cellulose synthase during secondary wall deposit ion, its gene family, its manipulation in transgenic plants, and mechanisms that may regulate its association with sites of polysaccharide synthesis. For cellulose synthase, we discuss the organization of the gene family and how protein diversity could relate to control of carbon partitioning to cel lulose synthesis. Other enzymes emphasized include UDP-Glc pyrophosphorylas e and sucrose phosphate synthase. New data are included on phosphorylation of cotton fiber sucrose synthase, possible regulation by Ca2+ of sucrose sy nthase localization, electron microscopic immunolocalization of sucrose syn thase in cotton fibers, and phylogenetic relationships between cellulose sy nthase proteins, including three new ones identified in differentiating tra cheary elements of Zinnia elegans. We develop a model for metabolism relate d to cellulose synthesis that implicates the changing intracellular localiz ation of sucrose synthase as a molecular switch between survival metabolism and growth and/or differentiation processes involving cellulose synthesis.