Thesis--University of Wisconsin--Madison. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 222-228).

Thesis (M.S.)--Wisconsin. / Includes bibliographical references (leaves 108-111).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1954. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves [136]-137).

Thesis (M.S.)--Oregon State University, 2000. / Typescript (photocopy). Includes bibliographical references (leaves 58-67). Also available on the World Wide Web.

Thesis (Ph. D.)--Oregon State University, 2006. / Printout. Includes bibliographical references (leaves 66-71). Also available on the World Wide Web.

Thesis (M.S.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 115-126). Also available on the World Wide Web.

Plants are continuously subjected to biotic stresses such as herbivory and pathogens. Consequently they have evolved many defense mechanisms. Inducible defenses that are activated only after insect infestation are one type of plant adaptation to herbivory. Many plant species possess arrays of inducible defenses, including the accumulation of toxic phytochemicals and antinutritive proteins that function to deter herbivory. Inducible defenses are generally activated at the transcriptional level and they can occur at the whole plant level, which presumably protects the plant from future herbivory. The genus Populus which includes both aspens and poplars, is an important tree for forestry but often undergoes severe defoliation by herbivores. Outbreaks of forest tent caterpillar (Malacosoma disstria, FTC) and the subsequent massive defoliation of its natural host, trembling aspen (Populus tremuloides Michx.), are known to periodically occur in North America. Within aspen populations, however, individual clones show variation in susceptibility to FTC, and this suggests the importance of innate defenses of aspen. Although it has been known that aspen leaves contain phenolic phytochemicals as defensive compounds, the involvement of defensive proteins was not known when this work began. Therefore, one aim of this study was to investigate protein-based induced defenses in trembling aspen, using a molecular approach. In order to initiate investigation of protein-based induced defenses in trembling aspen, genes for polyphenol oxidase (PPO) and trypsin inhibitor (Tl), known defense-related genes in other plant species, were isolated and characterized. Both PPO and TI were transcriptionally activated in aspen foliage by FTC herbivory, artificial tissue damage, and methyl jasmonate, a signal molecule for inducible defenses. In time course analyses, it was demonstrated that PPO and TI mRNAs accumulated within several hours in both wounded leaves and unwounded leaves of the same plant. This was consistent with the wound response previously reported from other plant species including hybrid poplar (Populus trichocarpa x P. deltoides) and is indicative of the presence of signaling mechanisms for systemic induction of defense proteins in trembling aspen. To further obtain insight into mechanisms for inducible defenses, signal molecules for induction of defenses were investigated using a model system, poplar suspension cultures, based on the observation that plant cell cultures often show rapid alkalinization of the medium in response to defense-related signal molecules. Using the alkalinization assay system, two different alkalinization factors were purified from poplar leaf extracts. First, three 5 kD peptides causing rapid alkalinization, the rapid alkalinization factors (RALFs), were isolated and further characterized at the molecular level. RALF appears to be a novel hormone-like peptide that was also recently characterized from tobacco. In contrast to other known alkalinization factors, RALF did not induce defenses such as the expression of phenylalanine ammonia lyase. Based on the expression profile of RALF genes, it was predicted that RALF may be involved in general cellular signaling such as growth and development rather than defense signaling. A second alkalinization peptide causing slower alkalinization, slow alkalinization factor (SALF), was also isolated and partially sequenced by Edman degradation. Database searches of the obtained peptide sequence revealed that SALF seems to be derived from the N-terminus of a known protein, photosystem 1 centre protein subunit D. Although it is not yet clear whether the SALF peptide is a defense-related signal in poplar, it is hypothesized that this breakdown product of a known protein may act as a biologically active signal in plants. Overall, this thesis presents: 1) the first demonstration of protein-based inducible defenses in trembling aspen at molecular level; 2) the discovery of novel peptide molecules with alkalinization activity in suspension cultures of poplar cells. / Graduate

Plant invertases (EC 3.2.1.26) represent a multi-gene family of β-fructofuranosidases that perform integral roles in several biochemical processes. The central importance of this family of enzymes to plant growth and development has made them a primary target of investigation in plant biology. Research has principally focused on sink-source interactions, and the potential to increase sink capacity in several economically important crop species, including potato and tomato. However, studies exploring the impacts of invertase mis-regulation on cellulose and lignin, the two most abundant biopolymers on earth, had not been conducted. Consequently, we investigated the effects of overexpressing yeast-derived invertases in tobacco and hybrid poplar. Transgenic tobacco expressing the yeast-derived invertases showed reduced height and interference in sink-source metabolism. In addition, some transgenic lines showed significant changes in cellulose and lignin content, providing evidence that sink capacity can be altered via the overexpression of this class of enzyme. In contrast, hybrid poplar expressing foreign invertase genes showed no visible phenotype, with only minor changes to the structural polymers cellulose and lignin, suggesting the mechanism of carbohydrate transport differs between tobacco and hybrid poplar. However, there was evidence for post-translational modification of the foreign invertases in hybrid poplar, which may also explain the difference in phenotypes observed. We suggest that the yeast-derived invertases may not be the most effective target to alter sink biopolymers, and that mis-regulating endogenous invertases may be a more suitable alternative. Consequently, we identified three cell-wall invertase genes in hybrid poplar and investigated their spatial and temporal expression profiles during the complete first year of growth. In addition, we heterologously expressed and characterized two hybrid poplar cell-wall invertase genes involved in vegetative growth. Collectively, the expression and functional characterization data suggest that one floral-specific and two vegetative cell-wall invertases exist in hybrid poplar. Of the two vegetative cell-wall invertases, one (PaxgINV1) appears to be involved in processes relating to dormancy, while the other (PaxgINV2) appears to be involved in phloem unloading and the seasonal reallocation of carbohydrate. We therefore hypothesize that PaxgINV2 may be a suitable target for future mis-regulation studies aimed at altering sink capacity.

Plant invertases (EC 3.2.1.26) represent a multi-gene family of β-fructofuranosidases that perform integral roles in several biochemical processes. The central importance of this family of enzymes to plant growth and development has made them a primary target of investigation in plant biology. Research has principally focused on sink-source interactions, and the potential to increase sink capacity in several economically important crop species, including potato and tomato. However, studies exploring the impacts of invertase mis-regulation on cellulose and lignin, the two most abundant biopolymers on earth, had not been conducted. Consequently, we investigated the effects of overexpressing yeast-derived invertases in tobacco and hybrid poplar. Transgenic tobacco expressing the yeast-derived invertases showed reduced height and interference in sink-source metabolism. In addition, some transgenic lines showed significant changes in cellulose and lignin content, providing evidence that sink capacity can be altered via the overexpression of this class of enzyme. In contrast, hybrid poplar expressing foreign invertase genes showed no visible phenotype, with only minor changes to the structural polymers cellulose and lignin, suggesting the mechanism of carbohydrate transport differs between tobacco and hybrid poplar. However, there was evidence for post-translational modification of the foreign invertases in hybrid poplar, which may also explain the difference in phenotypes observed. We suggest that the yeast-derived invertases may not be the most effective target to alter sink biopolymers, and that mis-regulating endogenous invertases may be a more suitable alternative. Consequently, we identified three cell-wall invertase genes in hybrid poplar and investigated their spatial and temporal expression profiles during the complete first year of growth. In addition, we heterologously expressed and characterized two hybrid poplar cell-wall invertase genes involved in vegetative growth. Collectively, the expression and functional characterization data suggest that one floral-specific and two vegetative cell-wall invertases exist in hybrid poplar. Of the two vegetative cell-wall invertases, one (PaxgINV1) appears to be involved in processes relating to dormancy, while the other (PaxgINV2) appears to be involved in phloem unloading and the seasonal reallocation of carbohydrate. We therefore hypothesize that PaxgINV2 may be a suitable target for future mis-regulation studies aimed at altering sink capacity.

Thesis (Ph. D.)--Landbouwhoogeschool te Wageningen, 1937. / Summary, table of contents and list of ill. in English.