Xyloglucans are plant cell wall matrix polysaccharides that are synthesized by enzymes in the membranes of the Golgi apparatus. Xyloglucan plays a central role in both cell wall structure and function. In addition, it may have a regulatory function in the process of controlling plant growth and development. It is a complex polysaccharide, yet compared to some it is relatively simple. This proposal describes a program of research designed to clarify the activities of xyloglucan synthase enzymes and the products they make. The overall objective of this project is to refine the xyloglucan biosynthesis system for use as a model for the study of both plant cell wall polysaccharide biosynthesis and the structure and functional organization of the plant Golgi apparatus. These two research topics are closely related and completion of this research will significantly increase our understanding of both. Golgi membranes isolated from suspension- cultured Acer pseudoplatanus (sycamore maple) cells are being subfractionated and these partially purified membrane fractions are being used as a source of xyloglucan synthases. Combinations of glycosyl composition analysis, methylation linkage analysis, and radiogas proportional counting are being used to determine identities of incorporated radiolabeled residues and the linkages between them. The glycosyl transferases involved with xyloglucan synthesis is being purified so that eventual subcellular localization and compartment mapping of plant Golgi are possible. Successful completion of this study will result in a greater understanding of the process of plant cell wall synthesis as well as the structure and function of the plant apparatus. There are many unanswered fundamental questions in plant biology. What influence cell wall biogenesis has on plant growth and development is one such question. This research offers an opportunity for progress in this area. Xyloglucans are an important component of plant cell walls both structurally and functionally. They allow the cell wall to maintain a degree of flexibility and are implicated in auxin-stimulated elongation during growth. This research is an in-depth study of the biosynthesis of these important cell wall sugars and provides a better understanding of the Golgi apparatus which produces the enzymes responsible for their synthesis.
