Electronic Theses and Dissertations (PhDs)

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Browsing Electronic Theses and Dissertations (PhDs) by Keyword "Biotic stress factors"

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    The effects of concurrent extreme temperature and water deficit on the phytochemical profile and phytopharmacological activities in Portulacaria afra Jacq
    (University of the Witwatersrand, Johannesburg, 2024) Adeleye, Oluwafunbi Christianah; Risenga, Ida
    In nature, all plants are exposed to stress which are mostly biotic and abiotic stress factors. Previous studies have demonstrated the impact of various abiotic stress factors on the production of secondary metabolites in therapeutic plants. Plant responses to stressors brought on by a combination of antagonistic abiotic factors have shown to be phenomenal compared to when plants are exposed to single a factor. According to latest climate change models, it is believed that plants would suffer unique or demanding concurrent abiotic stresses in the years to come. South Africa has been experiencing increasing temperatures over last 40 years and being regarded as a climate change ‘hot spot’ by the Intergovernmental Panel on Climate Change (IPCC). Therefore, it is critical to conduct research on the impact of climate change on the bioactive compounds in therapeutic plants. The overarching aim of this study was to establish and scientifically document, for the first time to our knowledge, the phytochemical profile, medicinal properties and phytopharmacological attributes of Portulacaria afra, a widely renowned medicinal plant used for treating several skin conditions and oral infections which also includes the assessment of the effects of concurrent extreme temperatures and water deficit/drought on species’ biological activities. In this study, South African Portulacaria afra plants were selected from healthy parent plants and propagated from cuttings. Samples were allowed to grow and establish a root system in the greenhouse for up to three months. After three months, 180 potted plant samples were exposed to treatments and not watered for up to 144 hours (6 days), and 45 control samples were placed under 25oC (ambient) and watered every second day with 500ml of water. The control samples were kept at 25°C maximum night-time temperature (7pm to 5am) and 27°C maximum day time temperature. Plants undergoing treatment (coded as treatment A, B, C, D) were treated as follows: A and B were exposed to 0/10ºC (night/day) and 5/15ºC (night/day) respectively, while C and D were exposed 20/40°C (night/day) and 35/45°C (night/day), respectively. Five potted plants were harvested in each treatment three times for up to 6 days (144hrs). Sample harvesting was scheduled episodically every 48hrs (48, 96, 144) and were then airdried under 40°C for 2 to 3 days. The aqueous (water) extracts at a temperature of 60°C, alongside methanol, n-hexane, and ethyl acetate extracts were derived from the leaves, stems, and roots. The extracts were then used to investigate the phytochemical composition, antibacterial efficacy, antioxidant capacity and antidiabetic potential. The qualitative phytochemical screening encompassed the preliminary assessment of saponins, flavonoids, glycosides, quinones, phenols, terpenoids, steroids, phytosteroids, volatile oil, carbohydrates, amino acids, and coumarins. The quantitative analyses were performed to determine the total phenolic content (TPC), total flavonoid content (TFC), while the antioxidant assays were performed to determine the reducing, scavenging and chelating abilities against DPPH, H2O2 and metal (Iron) chelating. The antibacterial activities against gram-negative Escherichia coli and gram-positive Staphylococcus aureus, Streptomyces griseus were assessed through agar well diffusion assay. The antidiabetic potential was evaluated using In vitro inhibitory α-amylase assay. Chemical profiling of various extracts from the leaves, stems, and roots of P. afra was conducted to identify and quantify some secondary metabolites. The methanolic leaf extracts exhibited a notable presence of quinones, phenols, steroids, and coumarins, whereas the aqueous leaf extracts contained moderate presence of saponins, terpenoids, quinones, and coumarins. Ethyl acetate leaf extracts were characterized by a strong presence of tannins and a moderate presence of phytosteroids. Conversely, n-hexane leaf extracts showed considerable saponin levels, moderate tannins, and terpenoids. Significantly strong presence of secondary metabolites was observed in methanolic stem extracts, particularly terpenoids, steroids, phenols, and coumarins. Notably, coumarins, known for their anticancer properties, were prominently present in methanolic leaf and stem extracts, with a moderate presence in root extracts, hinting at potential pharmaceutical applications and future roles in public health. Aqueous stem extracts exhibited strong glycoside presence, while ethyl acetate and n-hexane stem extracts exhibited few fewer secondary metabolite groups, ranging from moderate to weak presence. Distinctive chemical profiles were observed in root extracts, with ethyl acetate extracts showing significantly stronger quinone presence. Methanolic root extracts displayed moderate presence of coumarins and glycosides, whereas aqueous root extracts showed a low glycoside presence. The highest total phenolic contents (TPCs) and total flavonoid contents (TFCs) were found in methanol stem extracts and aqueous root extracts, respectively. Notably, aqueous root extracts exhibited the highest TPC and TFC among all root extracts. Antibacterial activity assays showed a wide range on inhibitory effects of n-hexane extracts from leaf, stem, and root against test microorganisms. Ethyl acetate leaf extracts demonstrated considerable inhibitory efficacy against Staphylococcus aureus, while methanolic extracts showed zero zone of inhibition. Aqueous root extracts showed strong antibacterial activity against Staphylococcus aureus, whereas other extracts showed no significant activity. Inhibition zones ranged from 13 to 24 mm for the plant extracts. The assessment of antioxidant potential through DPPH, H₂O₂ scavenging, and metal chelating assays showed varied activity among extracts. Ethyl acetate root extracts showed the strongest H₂O₂ scavenging activity, while aqueous stem extracts showed the strongest antioxidant activity against DPPH radicals. Aqueous and n-hexane root extracts showed the strongest metal chelating ability. The in vitro antidiabetic activity showed that all plant parts were active against α-amylase, with the highest inhibitory action recorded from the methanolic leaf extracts, followed by the methanolic root extracts