Cellulose Biosynthesis : Current Views and Evolving Concepts INDER

.-, Aims To outline the current state of knowledge and discuss the evolution of various viewpoints put forth to explain the mechanism of cellu lose biosynt·hesis. (. Scope Lnderstanding the mechanism of cellulose biosynthesis is one of the major challenges in plant biology. The simplicity in the chemical structure of cellulose belies the complexities that are associated with the synthesis and assembly of this polysaccharide. ,\'ssembly of cellulose microfibrils in most organisms is visuallzed as a multi-srcp process invol ving a number of proteins with the key protein being the cellulose synthase catalytic sub-unit. Although genes encoding this protein have been identified in almost all cellulose synthesizing organisms, it has been a challenge in general, and more specifically in vascular plants. to demonstratc cellulose synthase activity in vilro. Th.: assembly of glucan chains into cellulose microfibrils of specific dimcnsions, viewed as a spontaneous process, necessitates the assembly 01 synthesjzing sites unique to most groups of organisms. The steps of polymerization (requiring the specific arrangement and activity of the cellulose synthase catalytic sub-units) and crystallization (directed self-assembly of glucan chains) are cenainly interlinked in the formation of cellulose microfibrils. Mutants affected in cellulose biosynthesis have been identified in vascular plants. Studies on these mutants and herbicide­ treated plants suggest an interesting Ilnk between the steps of polymerization and crystallization during cellulose biosynthesis. ~ Conclusions With the identification of a large number of genes encoding cellulose synthases and cellulose synrhase-like proteins in vascular plants and the supposed role of a number of other proteins in cellulose bio­ synthesis. a complete understanding of this process will necessitate a wider variety of research tools and approaches than was thought to be required a few years back.