Project 11: Ultrastructural analysis of wood forming tissues
PI: Geoffrey Daniel
Staff: Lada Filonova, researcher; David Sandquist, PhD student
The inherent micro- and (nano)ultrastructure of wood cell walls ultimately determines fiber properties and their subsequent possibilities for industrial use. At the nanostructural level, the wood fiber cell wall has a highly complex architecture with both primary and secondary cell walls in which the major- (cellulose, hemicellulose, lignin) and minor components (pectins and proteins) are heterogeneously dispersed and integrated into a highly complex but unique biopolymer. The true micro- and ultrastructure of the secondary fiber cell wall is however currently unknown despite intensive studies over the years where most efforts have been directed to understanding primary wall structure. Fiber secondary wall structure is however a topic of major interest for research groups throughout the world as fibers and particularly its sub-components are being variously assessed and modified for use in future biocomposites and other specialized tailor-made end-products.
The FuncFiber project will provide an excellent opportunity for the adoption of "state of the art technology" for studying morphological and chemical ultrastructural aspects of fibers during wood cell wall formation in well-characterized poplar isolates (i.e. clones). It will also provide characterized material for studying morphological features of mature fibers for use in end-products. Poplar fibers and particularly tension fibers (i.e. from reaction wood) will provide excellent material for study since such fibers possess contrasting secondary wall layers that either contain all the major wood components (i.e. cellulose, lignin, hemicelluloses) or are composed almost entirely of crystalline cellulose (i.e. G-layer). Our initial efforts will focus on the micro/ultrastructural events during deposition of G-layer cellulose and its morphological structure in comparison to adjoining cell wall layers. Our first studies suggest the G-layer may have a multiple cellulose microfibril organization (i.e. composed of cellulose aggregates) and thus have a novel means of development. Understanding G-layer organization and events of cellulose deposition should give important details on basic secondary wall structure where significant hemicellulose and lignin is lacking.
The project work will involve the application of a variety of microscope techniques including conventional (e.g. light, transmission (TEM) and scanning electron microscopy (SEM)) and more advanced electron microscopy approaches (e.g. Cryo-SEM/TEM, 3-D tomography) for studying poplar secondary cell wall architecture, particularly G-layer synthesis. A range of immunoprofiling techniques (e.g. use of specific antibodies and carbohydrate binding modules; CBMs) will be applied in order to visualize the spatial distribution and sites of deposition of cell wall components/molecules allowing for the chemical characterization of fibers in wood forming tissues in-vivo. With the aid of 3-D TEM-tomography, it is further envisaged that aspects of the three-dimensional in-situ ultrastructural organization and interactions of cellulose, hemicellulose and lignin in fiber wall layers can be unravelled.