No description available.

published_or_final_version / Ecology and Biodiversity / Doctoral / Doctor of Philosophy

No description available.

Thesis (Ph. D.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 120-137).

A statistically sound and quantifiable bioassay procedure was developed for determining the response of adult Delia radicum to oviposition stimulants. The method was based on the use of surrogate leaves coated with test compounds. All of the test compounds were of purity 99% or greater. Twelve of the tested compounds were synthesised the remaining twenty four were either donated or available commercially. Attempts to follow literature methods to synthesise glucosinolates were unsatisfactory and an investigation of the procedures led to a number of synthetic modifications. Despite various attempts, the failure to sulphate a thiohydroximate to produce a glucosinolate was not resolved. Attempts to correlate oviposition stimulus with chemical structure produced a very significant finding. The results showed that a wide variety of chemically dissimilar compounds were effective stimulants providing they contained an S=O group. Thus sulphoxides, sulphones, sulphinic, sulphonic acids and their derivatives were all effective. Thiols and thioethers were non-stimulant, as were naturally occurring glucosinolates which had been chemically modified by the removal of the oxime sulphate group. The relative effectiveness of the oviposition stimulants was examined by determining the number of eggs laid on surrogate leaves relative to a prop-2-enylglucosinolate (sinigrin) standard over a range or concentrations. Statistical modelling of the data collected produced a maximum relative number of eggs laid (YMAX) at an optimum concentration (C) for each compound. It was not found possible to produce a single parameter combining YMAX and C, neither did any other structure-activity feature emerge from the study.

Thesis (M.Sc.) - Carleton University, 2003. / Includes bibliographical references (p. 98-106). Also available in electronic format on the Internet.

No description available.

<p>  </p> <p>Plant chemistry influences plant-nutritional quality, which in turn impacts plant-insect interactions. Plant secondary metabolites are pervasive in the plant kingdom and have been shown to influence both plant nutritional quality and plant-insect interactions. Levels of these secondary metabolites, as well as quantity, can impact availability of key macromolecules herbivorous insects need for optimal nutrient intake. Herbivorous insects can modulate their growth, rate of consumption, and frass production in response to diet with poor nutritional quality. Insects can also increase the production or activity of nutritional and detoxification enzymes to offset diet with poor nutritional quality. While the influence of plant secondary metabolites on nutrient intake is better understood in many plant systems, it is not well understood in plant-insect interactions involving <em>Cannabis sativa</em>. An increase in large-scale agricultural production of <em>Cannabis</em> has introduced a novel secondary metabolite, cannabinoids, a terpenophenolic compound with known physiological effects in many animal systems, onto the landscape. While insects have been shown to exhibit reduced performance on higher cannabinoid diets, insects lack human-analog cannabinoid receptors, so how these compounds interact with insect herbivores is not well understood. A goal of this study was to increase the understanding of how cannabinoids influence herbivorous insect performance. </p> <p>To understand the influence of cannabinoids on insect performance and enzyme activity I performed no-choice feeding bioassays on fall armyworm (<em>Spodoptera frugiperda</em>) with artificial diet spiked with different concentrations of cannabidiol (CBD). I measured growth, consumption, and frass production. From these same larvae, I also analyzed detoxification and nutritional enzyme activities. I found that as CBD concentration increased in diet, growth and consumption of fall armyworm decreased. I also found that as CBD concentrations increased, protease and cytochrome P450 enzyme activity decreased, and β-glucosidase enzyme activity increased. These outcomes highlight potential mechanisms for both behavioral and biochemical mechanism by which CBD confers resistance to insect herbivores.</p> <p>As agricultural production of <em>Cannabis</em> continues to increase, cannabinoids will continue to alter the chemical landscape of agricultural systems. How insect herbivores contend with cannabinoids is an important step in understanding plant-insect interactions in <em>Cannabis </em>systems. Identification of the structural and functional characteristics of protease and cytochrome P450 enzymes influenced by cannabinoids are possible future avenues of research that can better develop our understanding of <em>Cannabis</em>-insect interactions.</p>

I used a data-set of 986 plant species (from 493 genera in 195 families) obtained from a literature search and a new data collection for 58 tropical tree species (from 31 genera in 18 families) growing in two contrasting forest types in Brunei Darussalam: mixed dipterocarp forest on moderately infertile ultisols and fluvisols, and heath forest on acidic and nutrient-poor spodosols.  I provide statistical evidence for the existence of discreet groups of species representing Al accumulators and non-Al accumulator based on foliar Al concentrations.  The threshold foliar Al concentration was higher for tropical plants (range 2.3-3.9 mg Al g^-1) than temperate plant (1.1 mg Al g^-1). Species’ mean log foliar Al concentration was also higher for tropical (0.73 ± 1.11 mg Al g^-1) than temperate plants (0.16 ± 1.07 mg Al g^-1).  I used the tropical Al accumulating shrub <i>Melastoma malabathricum </i>L. as a study species to test the hypotheses that growth would be stimulated by Al addition.  Growth of <i>M. malabathricum </i>seedlings was stimulated by Al addition when the external supply of macronutrients was very low, and this growth response was associated with an increase in net assimilation rate and specific leaf area.  Foliar Al concentration was positively correlated with foliar concentrations of Ca and Mg across 16 Al accumulator species sampled in the field study in Brunei Darussalam, while foliar Al and K concentrations were correlated positively in <i>M. malabathricum </i>seedlings growing in the solution culture experiments.  These positive correlations contradict the hypothesis that Al inhibits the uptake of nutrient cations and they may contribute to the positive growth response to Al addition in Al accumulator plants.

Orientador: Pedro Luís da Costa Aguiar Alves / Coorientador: Fernando Batista da Costa / Coorientador: Marcelo Claro de Souza / Banca: Sonia Cristina Juliano Gualtieri / Banca: Dagoberto Martins / Banca: Ricardo Victória Filho / Banca: Mariluce Pascoina Nepomuceno / Resumo: As condições ambientais, assim como o contraste sazonal nas fitofisionomias do Cerrado entre a época seca e úmida colaboram para a diversificada sintetize e seleção de metabólitos secundários em plantas. Os metabólitos secundários atuam como uma interface química entre plantas e o meio, desta forma a sua síntese pode ser comumente alterada pelas condições ambientais. Fatores como temperatura, disponibilidade hídrica, luminosidade, características do solo, nutrientes e poluição atuam diretamente sobre a produção e liberação desses compostos. Os microrganismos do solo podem transformar os compostos tóxicos liberados, desativando-os ou dando origem a compostos ainda mais tóxicos, assim como esses compostos podem alterar as características e atributos do solo quando presentes em quantidades adequadas. Dentre as plantas nativas do Cerrado destaca-se a espécie Vernonia ferruginea, uma agressiva infestante de pastagem, que possui indícios de produção de compostos com potencial tóxico. Desta forma, esta pesquisa foi desenvolvida para verificar a atividade tóxica de V. ferruginea e se a mudança de algumas características como disponibilidade hídrica, tipo de solo, condições de luminosidade e concentração de alumínio no solo influenciam a produção desses compostos. Para tal, plantas de V. ferruginea foram desenvolvidas sobre diferentes condições para posterior extração e/ou fracionamento do material vegetal para verificação de atividade biológica por meio de bioensaios e identificação ... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The environmental conditions, as well as the seasonal contrast in the Cerrado phytophysiognomies between the dry and wet seasons, contribute to the diversified synthesis and selection of secondary metabolites in plants. Secondary metabolites act as a chemical interface between plants and the environment, so their synthesis can be commonly altered by environmental conditions. Factors such as temperature, water availability, luminosity, soil characteristics, nutrients and pollution act directly on the production and release of these compounds. Soil microorganisms can transform the released toxic compounds, deactivating them or giving rise to even more toxic compounds, as these compounds can alter the characteristics and attributes of the soil when present in adequate amounts. Among the native plants of the Cerrado, the species Vernonia ferruginea, an aggressive pasture weed, stands out, with indications of production of compounds with toxic potential. Thus, this research was developed to verify the toxic activity of V. ferruginea and if the change of some characteristics such as water availability, soil type, light conditions and aluminum concentration in the soil influence the production of these compounds. For this, plants of V. ferruginea were developed on different conditions for later extraction and / or fractionation of the vegetal material for verification of biological activity by means of bioassays and identification of chemical groups. Considering the results of the parameters of germinability and development of the tested species it is possible to inquire about the possibility of V. ferruginea being able to release toxic substances, since direct consequences of the presence of these compounds in the extracts were verified in the bioassay, such as: The inhibition / reduc... (Complete abstract click electronic access below) / Doutor