Emery, Neil NE

The study examines the phytochemical and phytohormone profiles of two ecotypes of Doliocarpus dentatus (Capadulla) from Guyana with an emphasis on their potential therapeutic applications, particularly in the context of erectile dysfunction. The research concentrates on the red and white ecotypes, which are visibly differentiated by the colouration of their inner and outer bark; moreover, the red ecotype is widely regarded by traditional knowledge to be more efficacious in treating erectile dysfunction. The study seeks to provide much-needed scientific evidence to support the traditional medicinal uses of D. dentatus and aims to accomplish this by providing semi-targeted and targeted analysis of its bioactive compounds.The thesis employs a multi-faceted approach, commencing with Chapter 2, an examination of the international and national frameworks that govern natural product research in Guyana, thereby ensuring ethical and sustainable practices. Chapter 3, Liquid chromatography-mass spectrometry-based metabolomics was utilized to analyze the phytochemical profiles of the red and white ecotypes of D. dentatus. Approximately 847 compounds were identified, with 138 tentatively classified as potentially therapeutic, particularly polyphenols exhibiting antioxidant properties. Chapter 4 focus on the phytohormone profiling revealed that the red ecotype generally exhibited higher levels of active cytokinins, particularly trans-zeatin (tZ) and cis-zeatin (cZ), compared to the white ecotype. A strong correlation was identified between specific cytokinins and secondary metabolites such as flavonoids and alkaloids, suggesting complex interactions that may enhance the therapeutic potential of D. dentatus. Chapter 5 further analysis of total phenolic content, flavonoid content, and their antioxidant capacities demonstrated differences between the red and white ecotypes, with the red ecotype generally showing higher levels of these compounds. Both ecotypes demonstrated significant antioxidant activity, with the red ecotype showing enhanced radical scavenging capacity. The study also revealed a diverse range of bioactive compounds, including flavonoids, terpenoids, and alkaloids, which may contribute to the plant's reported medicinal properties. This semi-targeted and targeted analysis provides novel insights into the phytochemical and phytohormone profiles of D. dentatus ecotypes, offering a scientific basis for their traditional medicinal uses and potential therapeutic applications. The findings suggest that D. dentatus, particularly the red ecotype, may have significant potential for developing new drugs, especially in the context of erectile dysfunction therapy.

Author Keywords: antioxidant, Bioactive compounds, liquid chromatography-electrospray ionization tandem mass spectrometry, metabolomics, secondary metabolites, therapeutic properties

Darwinian fitness is determined by the outcome of allocations of energy and nutrients to plant growth, survival, and reproduction. Allocations to reproduction differ from allocations to growth and survival because the products of reproduction (pollen, ovules, and fruits) are dispersed away from the plant and so the resources used to produce them cannot be re-allocated. As a result, and because the total resource pool available to a plant is limited, allocations to reproduction can reduce future growth, reproduction, and/or survival, yielding fitness costs of reproduction. This study provides a novel approach to detecting the costs of reproduction through multiple reproductive currencies, including both biomass and nitrogen allocations and their temporal effects on current and future plant performance. My results demonstrate the environmental dependence of the costs of reproduction and show that under certain conditions, males can bear greater costs than females, contrary to the prevailing view.

Author Keywords: Cost of reproduction, dioecy, flower removal, life-history trade-offs, photosynthetic machinery, sexual dimorphism

The seed oil of Carapa guianensis, known as Crabwood oil (CWO) and its fractionation was studied, focussing on chemical composition and physicochemical functionality. Compounds never reported before in CWO were identified, including limonoids such as Trichillin, ketostearic and hydroxyoleic acids. Yield of olein and stearin fractions correlated strongly with solvent polarity. Important bioactives were partitioned as a function of solvent polarity in the olein vs. stearin fractions. For example, up to 35% more of Gedunin were present in the liquid fractions. Solid fat content, crystallization and melting temperature and microstructure were significantly affected by fractionation and shown to be strongly correlated with solvent polarity. Fractionation was demonstrated to be a powerful tool to extend the physical functionality of CWO and concentrate its bioactives.

Author Keywords: Carapa guianensis, Chemical characteristics, Crabwood Oil, Dry and Solvent fractionation, Fractionation, Physical characteristics

The oyster mushroom, Pleurotus ostreatus, is one of the most widely cultivated edible basidiomycetes. It has gained increased attention for its economic, environmental, and medicinal properties. While a lot is known about cytokinins (CKs) and their actions at the molecular and cellular levels in plants, much less is known about the function of CKs in other kingdoms. Cytokinins, which have been detected in several fungal species, play a role in pathogenic attack against plants or during plant growth promotion by plant beneficial microbes; however, the role of CKs in fungal physiology, separate from plant associations remains largely unknown. This thesis focuses on the occurrence of fungal-derived CKs in P. ostreatus when grown in vitro as submerged or aerial mycelium. Cytokinin profiling by UHPLC-HRMS/MS revealed that P. ostreatus produces CKs and that the tRNA degradation pathway is the main source of these molecules. CK dynamics within fungal growth supported previous evidence, which suggested that tRNA degradation products have a role in the physiological development of fungi for which CKs act as fungal growth regulators. A second component of the thesis demonstrated that P. ostreatus responds to exogenous applications of aromatic and isoprenoid CKs and their effects were dependent on the dose and CK type. N6-Benzyladenine (BAP), Kinetin (KIN), N6-isopentenyladenine (iP), and trans-zeatin (tZ) bioassays revealed hormone-type responses (hormesis: biphasic response). At low doses, mycelium growth could be stimulated, whereas, at high doses only inhibitory effects were observed. This stimulation/inhibition was observed whether the measured response was an increase/decrease of aerial mycelium colony diameter, biomass accumulation or a change in mycelium morphology as compared to the controls. Results indicated there is potential to alter mycelium growth and development of P. ostreatus; thus, CKs may play the role of a "mycohormone" and may be specifically helpful for medicinal fungi by increasing growth and efficiency to produce many biologically active substances with valuable medical and environmental applications.

Author Keywords: cytokinins, fungal-derived CKs, hormesis, mycelium, mycohormone, Pleurotus ostreatus