Thesis (M.S.)--Humboldt State University, 2007. / Includes bibliographical references (leaves 39-45). Also available via Humboldt Digital Scholar.

Thesis (M.S.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 68-72). Also available on the World Wide Web.

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

Thesis (MS)--University of Montana, 2010. / Contents viewed on May 28, 2010. Title from author supplied metadata. Includes bibliographical references.

Thesis (M.S.)--Oregon State University, 2006. / Printout. Includes bibliographical references. Also available on the World Wide Web.

Thesis (M.S.)--Oregon State University, 1985. / Typescript (photocopy). Includes bibliographical references (leaves 151-161). Also available on the World Wide Web.

Regeneration of forest stands is often complicated by the establishment and competition of brush on logged and burned-over areas. The encroachment of brush in the ponderosa pine type of Idaho, particularly Ceanothus velutinus, Dougl. presents a difficult problem to the forest manager. The brush competition severely reduces the growth rate of associated trees, thus extending the period necessary to grow a crop of trees. This situation may seriously limit the economic production of a wood crop of ponderosa pine. Any approach to the solution of brush problems should include a thorough understanding of brush ecology. Those phases of ecology dealing with reproduction and distribution of brush need special emphasis. It has been assumed that most of the brush on logged or burned-over areas originated from seed stored in the forest floor; yet little is known of the quantity or distribution of these seeds. This study was carried out to learn what kind, number and variability of seed is present in the forest floor, and to investigate the number of seed located in different forest conditions, aspects and soil layers. To achieve the above objectives, 48 square-foot, duff-soil samples were taken in the ponderosa pine type of the Boise Basin Experimental Forest in Idaho. Seeds were separated from the samples and major species identified, pretreated and germinated. Appropriate statistical techniques were employed to determine significant results among the different forest conditions, aspects and soil layers sampled.

Titre de l'écran-titre (visionné le 25 septembre 2023) / Dendroctonus ponderosae, appelé le dendroctone du pin ponderosa (DPP), est l'un des insectes ravageurs les plus destructeurs de l'ouest de l'Amérique du Nord. Les champignons qu'il transporte causent de la mortalité chez plusieurs espèces du genre Pinus. L'infestation d'un pin commence par la libération d'une phéromone d'agrégation, le trans-verbénol, par un DPP femelle adulte, initiant ainsi une attaque de masse. En grand nombre, le DPP réussit à surmonter les défenses du pin incluant la production d'oléorésine contenant des composés toxiques comme l'α-pinène. La phéromone est initialement produite par l'insecte au stade larvaire par hydroxylation de l'α-pinène dans un processus de détoxification. Le trans-verbénol ainsi produit est ensuite lié à un acide gras afin d'être entreposé sous forme d'esters. Quand l'adulte colonise un nouveau pin, une carboxylestérase prédite causerait la libération de la phéromone séquestrée. L'hypothèse émise est que cette réaction est catalysée par l'estérase du clone DPO062_I20 du DPP. La production recombinante de l'enzyme a été faite dans Escherichia coli, mais celle-ci formait des corps d'inclusion. Les corps d'inclusion ont été solubilisés et la protéine solubilisée a été repliée, mais aucune activité enzymatique n'a été mesurée lors des essais préliminaires avec les esters de trans-verbénol identifiés dans le DPP. Une analyse des homologues de l'estérase a révélé qu'un organisme eucaryote pourrait être mieux adapté pour l'expression d'une enzyme active. L'estérase a donc été produite dans la levure Pichia pastoris dans laquelle elle a été retrouvée sous forme glycosylée. Cependant, aucune activité enzymatique n'a été mesurée dans les conditions testées. Différentes conditions d'expression et d'essais enzymatiques devront être étudiées afin d'obtenir une conclusion fiable quant à la caractérisation enzymatique de l'estérase. Finalement, un arbre phylogénétique des carboxylestérases du DPP a révélé que la carboxylestérase d'intérêt pourrait être spécifique à l'ordre Coleoptera ou à la sous-famille Scolytinae. / Dendroctonus ponderosae, known as the mountain pine beetle (MPB), is one of the most destructive insect pests in western North America. The fungi carried by MPB cause mortality in several Pinus species. Pine colonization is started by an adult female MPB releasing an aggregation pheromone called trans-verbenol, thus initiating a mass attack. In large numbers, MPB can overcome the host's defenses, which includes the production of oleoresin which contains toxic molecules such as α-pinene. The pheromone is initially produced at the larval stage through hydroxylation of α-pinene as a detoxification process. The resulting trans-verbenol is then conjugated with a fatty acid in order to be stored in the form of esters. When an adult MPB colonizes a new host, a predicted carboxylesterase causes the release of the sequestered pheromone. It is hypothesized that the esterase from the MPB clone DPO062_I20 catalyzes this reaction. The enzyme was recombinantly produced in Escherichia coli but formed inclusion bodies. These inclusion bodies were solubilized and the proteins were refolded, but no enzyme activity was detected in preliminary assays using trans-verbenol esters identified in MPB. Analysis of the esterase's homologs suggested that a eukaryotic organism could be more suitable for the expression of an active enzyme. The esterase was thus produced in the yeast Pichia pastoris, in which it was found to be glycosylated. However, no enzyme activity was measured under the tested conditions. Further exploration of different expression and assay conditions will be necessary to obtain a reliable conclusion regarding the enzymatic characterization of the carboxylesterase. Lastly, a phylogenetic tree of MPB carboxylesterases revealed that the carboxylesterase of interest may be specific to the Coleoptera order or to the Scolytinae subfamily (bark beetles).

An earlier publication presented evidence for enhancement of isocitrate lyase (threo-L_S isocitrate glyoxylate lyase, EC 4.1.3.1) activity by a factor that diffuses into the megagametopnyte from the embryo of stratified germinating Pinus ponderosa seeds. In contrast, the data reported here indicate the rate of increase in specific activity of embryoless seeds was greater during the first four days than in seeds with embryos left in situ. A similar pattern of activity was observed in seeds which retained their embryos for two days to allow germination to occur prior to excision, but the peak activity was slightly nigher. The highest enzyme activity was achieved in seeds which retained their embryos the longest. A model is included to resolve these apparently diverging effects of the embryo on isocitrate lyase activity. A diffusate prepared from two day germinated embryos had no significant influence on the enzyme activity of embryoless seeds. The phenomena reported here were not dependent on stratification. Imbibition was the only prerequisite for germination and develooment of enzyme activity to occur. / Master of Science

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