There are many unanswered fundamental questions in plant biology including the extent of influence cell wall biogenesis has over plant growth and development. The proposed research offers an opportunity for progress in this area. Xyloglucans are an important component of plant cell walls and there is evidence they may serve as signaling molecules in plants. Increased knowledge about the enzymes and genes that are responsible for xyloglucan biosynthesis will add significantly to understanding of cell wall polysaccharides and the process of cell wall synthesis. In addition, the proposed research will increase knowledge of the structure and functional organization of the plant Golgi apparatus. This proposal describes a program of research designed to complete purification of xyloglucan glucosyltransferase (XGT). Major objectives include: 1. Purification of XGT enzyme. 2. Reaction product characterization. 3. Accepter molecule requirements. 4. Characterization and enzyme kinetics of XGT. Beyond the scope of this proposal, we plan eventually to use purified XGT as an avenue to determi ne patterns of subcellular localization, spaciotemporal expression patterns, and molecular genetic control of the xyloglucan synthesis enzyme system. A fundamental understanding of the plant cell wall's role in regulating plant growth and development will be necessary to meet the practical goals of future plant biology research, namely, genetically engineered agricultural plants, increased crop yields and productivity, improved stress tolerance, and improved resistance to attack by disease organisms. %%% One of the fundamental differences between animal cells and plant cells is that each plant cell is surrounded by a cell wall made primarily of polysaccharides. Most of these polysaccharides are manufactured inside the cell in the membranes of the Golgi apparatus, and then are packaged and secreted to the wall outside the cell membrane. None of the plant cell wall polysaccharide- synthesizing enzymes has ever been purified for detailed biochemical study. This project has the goal of purifying xyloglucan glucosyltransferase (XGT), the enzyme responsible for synthesis of the glucan backbone of the polysaccharide xyloglucan. Xyloglucans are an important component of plant cell walls and there is evidence they may serve as signaling molecules in plants. Increased knowledge about the enzymes and genes that are responsible for xyloglucan biosynthesis will add significantly to understanding of cell wall polysaccharides and the process of cell wall synthesis. In addition, the proposed research will increase knowledge of the structure and functional organization of the plant Golgi apparatus. A more complete understanding of cell wall synthesis is crucial to an understanding of the plant cell wall's role in regulating plant growth and development.
