No description available.

No description available.

Plant cell walls compose the largest source of sugars on earth and are a potential source after conversion for liquid transportation fuels. However, the crystalline region of cellulose and the lignin that incases it present significant obstacles for enzymes to digest. This lowers the sugar yield, which ultimately decreases the production efficiency of bioethanol. A pretreatment that could help lowering the amount of crystallinity; meanwhile, breakdown the matrix of lignin and polysaccharides that cover cellulose fibers would be ideal. Here we propose a physical pretreatment strategy of electron beam irradiation that could potentially decrease cellulose crystallinity as well as unzip the lignin structure. Four types of biomass: cellulose, yellow pine, yellow poplar, and switchgrass were irradiated with a 12 MeV electron beam (Sterigenics, Inc.) at dosages of 0, 54, 80, 148 and 403 kGy. By combining the result from the wet chemical analysis of percent weight glucose/ cellulose from the HPLC, percent crystallinity from the Wide Angle X-Ray Diffraction (WAX) and the change of chemical functionality from Fourier Transform Infrared Spectrometer (FTIR), a promising effect is obtained in pine and yellow poplar but not in cellulose and switchgrass. A significant increase in percent glucose is observed for pine at higher doses as shown by (r = 0.97, P< 0.0076) which are 9.4 and 27% at 0 and 403 kGy. The amount of glucose considerably changes from all different types of biomass over time (P< 0.0001). A strong correlation of decreasing in percent crystallinity was found in poplar (r = -0.89, P< 0.05) from 32.4% to 17.4% and related to an average increase in percent glucose produced from 30 to 55% comparing between 0 and 403 kGy.

Thesis (Ph. D.)--Institute of Paper Chemistry, 1974. / Includes bibliographical references (p. 139.148).

Thesis (Ph. D.)--Institute of Paper Chemistry, 1980. / Includes bibliographical references (p. 58-59).

Thesis (Ph. D.)--Institute of Paper Chemistry, 1968.

Although dynamic interactions between plant cells and their environment require adhesion between the cell wall (CW) and the plasma membrane (PM), few plant adhesion molecules have been identified. Therefore, the seed coat mucilage secretory cells (MSCs) of Arabidopsis thaliana (which undergo developmentally regulated changes in adhesion) were developed into a novel model system to study PM-CW adhesion. Twenty-seven candidate genes were identified using data from publicly available and seed-specific microarrays. Mutant plants for these genes were screened for defects in adhesion via plasmolysis, and for changes in MSC morphology that may result from defective adhesion (Chapter 1). Two fasciclin-like arabinogalactan proteins were isolated in this screen. One of these, SOS5, was characterized in detail (Chapter 2). sos5 mutants are sensitive to hyperosmotic conditions and show defects in PM-CW adhesion and MSC mucilage structure. Interestingly, these phenotypes may be attributed to defects in adhesion or to defects in cell wall deposition.

The yeast SKN7 gene encodes a transcription factor that is involved in a variety of processes in cell physiology including cell wall synthesis, cell cycle progression, and oxidative stress resistance. Using a transcriptional reporter-based system, it has been demonstrated that Skn7p is regulated by the two-component osmosensor Sln1p in a manner that requires the phosphorelay molecule Ypd1p, but not the response regulator Ssk1p. Consistent with its regulation by an osmosensor, Skn7p is involved in negative regulation of the osmoresponsive HOG MAP kinase cascade. Cells lacking SKN7 and the protein serine/threonine phosphatase encoded by PTC1 are severely disabled for growth, and hyperaccumulate intracellular glycerol. The growth defect of skn7Delta ptc1Delta mutants can be bypassed by overexpression of specific phosphatase genes, or by deletion of the HOG MAP kinase pathway-encoding genes PBS2 or HOG1. / MID2 was isolated in a screen designed to identify upstream regulators of Skn7p. Mid2p is an extensively O-mannosylated protein that is localized to the plasma membrane. Mutants with defective beta-1,6-glucan synthesis grow more quickly when MID2 is absent. Conversely, MID2 is essential for viability in cells lacking FKS1, the gene encoding the primary catalytic subunit of beta-1,3-glucan synthase. mid2Delta mutants are resistant to calcofluor white, a drug that interferes with cell wall chitin synthesis, while cells overexpressing MID2 are supersensitive to the drug. mid2Delta mutants have a significant reduction in stress-induced chitin synthesis, while cells overexpressing MID2 hyperaccumulate cell wall chitin. Consistent with a proposed role in sensing and responding to cell wall stress, high copy expression of specific components of the cell wall integrity MAP kinase cascade suppress various mid2Delta phenotypes, and Mid2p is essential for full activation of the Mpk1p MAP kinase during various cell wall stress and morphogenic conditions. / Observations from genetic and biochemical experiments suggest that Mid2p is a regulator of the small G-protein encoded by RHO1. Deletion of MID2 is lethal to mutants lacking the Rho1p GEF Rom2p, but suppresses the low temperature growth defect of mutants lacking the Rho1p GAP Sac7p. Conversely, high copy expression of MID2 is a strong suppressor of mutants lacking TOR2, an upstream activator of Rom2p, but is toxic to sac7Delta mutants. High copy expression of MID2 causes increased GEF activity towards Rho1p. Mid2p appears to act in parallel to Rom1p and Rom2p in promoting GDP-GTP exchange for Rho1p in a mechanism that is not yet understood.

The effect of mechanical shear on brewing yeast was investigated with a focus on losses incurred through cell rupture and viability loss. The influence of various environmental conditions was studied with regards to the influence on Saccharomyces cerevisiae's ability to resist mechanical shear. Further investigation was performed in order to locate a structure within the yeast cell that contributes to mechanical shear resistance. / It was found that yeast cells grown anaerobically in limited glucose media were more prone to losses in cell viability than cells grown aerobically in the same media, when subjected to mechanical shear. Cells grown anaerobically in high glucose concentrations and allowed to ferment the media to exhaustion were slightly more resistant to mechanical shear compared to cells grown anaerobically without fermentation in minimal glucose media. Higher ethanol concentrations lead to marginally decreased resistance to mechanical shear. / Cell walls of S. cerevisiae were partially digested or extracted using enzymatic treatment or chemical attack. It was found that while the outer mannoprotein layer does not contribute significantly, the inner beta-(1 → 3)-glucan structure plays a significant role in resistance to mechanical shear.

This thesis examines the interaction of xyloglucan, the major hemicellulosic component of type I primary plant cell walls, with cellulose. Initial attempts to form xyloglucan-cellulose complexes by in vitro association methods are described, which gave low levels of interaction, with features not similar to those found in primary wall networks. The majority of the work focusses on the use of the bacterium Acetobacter aceti ssp. xylinum (ATCC 53524), which synthesise highly pure, crystalline cellulose as an extracellular polysaccharide. Addition of xyloglucan to a cellulose-synthesising bacterial culture results in the formation of cellulose-xyloglucan networks with ultrastructural and molecular features similar to those of the networks of higher plants. Applicatioon of the bacterial fermentation system is extended to incorporate the polysaccharides glucomannan, galactomannan, xylan, mixed-linkage glucan, pectin and carboxymethylcellulose, all of which impart unique architectural and molecular effects on the composistes formed. Preliminary data on the mechanical properties of composite structures under large and small deformation conditions are also described.