Non-targeted metabolite profiling by liquid chromatography-mass spectrometry (LC-MS) was used to determine the metabolite responses of Arabidopsis roots to auxin or ethylene. Crosstalk between these hormones regulates many important physiological processes in plants, including the initiation of lateral root formation and the response to gravity. These occur in part through alterations in the levels of flavonoids, specialized plant metabolites that have been shown to act as negative regulators of auxin transport. However, much remains to be learned about auxin and ethylene responses at the level of the metabolome. LC-MS analysis showed that a number of ions changed in response to both hormones in seedling roots. Although classes of specialized metabolites such as flavonols and glucosinolates change in abundance in response to both auxin and ethylene, there was little overlap with regard to the specific metabolites affected. These data will be integrated with information from transcriptomic and proteomic experiments to develop framework models that connect phytohormones and specialized metabolism with specific physiological processes. Previous studies by imaging techniques have shown that flavonols increase in response to both auxin and ethylene in the root elongation zone, but LC-MS showed that flavonols decreased in abundance in response to these hormones. Therefore a method was developed for targeted metabolite profiling of flavonols in individual root tips by flow injection electrospray mass spectrometry. This method uncovered spatial differences in metabolic profiles that were masked in analyses of whole roots or seedlings, and verified that flavonols increase in response to these hormones in root tips. / Master of Science

Consumption of cocoa and dark chocolate products has been associated with positive health outcomes including reduced onset of cardiovascular disease, inflammation, diabetes, obesity, and platelet disorders. Cocoa polyphenols, putatively responsible for these beneficial activities, are highly impacted by cocoa variety, agronomic effects and processing history. However, the difference in polyphenol concentration and composition between cocoa products originating from different hybrid clones (selected for high yield) or from different fermentation conditions is not fully understood. Detailed polyphenol characterization including determination of total polyphenol and total procyanidin concentrations, and qualitative and quantitative analysis of (mean) degree of polymerization was conducted. Significant differences in total polyphenol and procyanidin concentrations were observed between five genetic clones grown by the USDA-ARS Cocoa Germplasm Repository located in Mayagüez, Puerto Rico. To facilitate cocoa fermentation research in laboratories distant from cocoa harvesting sites, a laboratory-scale cocoa fermentation model system was developed in this study. This model system used dried, unfermented, cocoa beans and simulated pulp medium as the starting material. The model system supported growth of the essential succession of cocoa fermenting microorganisms and generated similar chemical changes to those observed in on-farm cocoa fermentation. Using this model system, the impact of inoculation with proprietary yeast strains Saccharomyces cerevisiae Lev F and Saccharomyces cerevisiae Lev B on cocoa polyphenol concentration and composition was evaluated. Inoculation with both yeast strains resulted in increased fermentation rate and Lev B inoculation resulted in higher total polyphenol and procyandin contents at the end of fermentation. Overall, the present work addressed the influence of cocoa variety selection and fermentation process conditions on the composition and concentration of polyphenols. These findings will contribute to continued efforts to develop cocoa products with optimized bioactivity and maximum disease preventative effects. / PHD