Theses and Dissertations (Animal, Plant and Environmental Sciences)

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Browsing Theses and Dissertations (Animal, Plant and Environmental Sciences) by Faculty "Faculty of Science"

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    Concurrent effects of elevated carbon dioxide and temperatures on the polyphenolics profile, in-vitro selected antioxidant and antimicrobial activities in Carpobrotus edulis (L.) leaves
    (University of the Witwatersrand, Johannesburg, 2022) Sebothoma, Lethabo; Risenga, Ida; Nuapia, Yannick; Mayonde, Samalesu
    Anthropogenic activities have led to the accumulation of carbon dioxide in the atmosphere and consequently the elevation of temperature. Carbon dioxide and temperature influence the physiological and biochemical activities in plants and thus, are important for plant survival, growth, and development. The sessile nature of plants prevents them from physically avoiding environmental factors such as high CO2 and temperatures, as a result they have developed a physiological response mechanism for protection. This mechanism involves the production of secondary metabolites, which in return have human-health benefits. How then is the production of secondary metabolites impacted by rising atmospheric CO2 concentrations and temperatures? Moreover, is the pharmaceutical efficacy of medicinal plants impacted as the atmospheric CO2 concentrations and temperature conditions rise due to climate change? This study therefore, aimed to investigate the possible modifications in the composition of polyphenolic compounds, antioxidant and antibacterial activities in Carpobrotus edulis leaves under controlled concurrent elevated atmospheric CO2 and temperatures. A total of 36 C. edulis potted plant samples, constituting 12 pots, divided into 3 pots per treatments were exposed to combined 600 ppm and 35/30°C (day/night), 600 ppm and 45/35°C (day/night), 800 ppm and 35/30°C (day/night), 800 ppm and 45/35 °C (day/night), respectively. The control samples were kept at ambient conditions of combined 400 ppm and 28/25°C (day/night). The plant samples were exposed to these conditions for up to 192 hours, and leave samples were harvested episodically every 48 hours (48, 96, 144 and 192 hours) during the exposure period. All harvested leave samples were air-dried under 40°C and crude extracts were obtained using methanol. Preliminary phytochemical screening was performed to test the presence of tannins, phenolics, flavonoids, steroids, terpenoids, 6 glycosides, and saponins. The LC-MS/MS method was used to profile the polyphenolic compounds and 2,2-diphenyl-1- picrylhydrazyl (DPPH) used to measure the antioxidant activity of the plant. The antibacterial activity of C. edulis was determined by the use of two popular bacterial strains, Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive), using the Agar well diffusion method. The preliminary phytochemical screening results showed the consistent presence of tannins, phenolics, flavonoids, steroids, terpenoids, glycosides, and saponins throughout the treatments as compared with the control, however flavonoids were not detected in the samples under combined 800 ppm and 45/35°C, 600 ppm and 35/30°C as well as 800 ppm and 35/30°C. This indicated that combined elevated CO2 and temperatures could have impacted on the production of flavonoids. The LC-MS/MS results showed the presence of 24 polyphenolic compounds in Carpobrotus edulis leaves and of those only 14 (58.83%) were present in C. edulis leaves under ambient/control conditions. Furthermore, the concurrent increment of CO2 concentrations and temperatures prompted the appearance of 10 (41.67%) more compounds. A total of 17 (70.83%) polyphenolic compounds were identified under the 600 ppm and 45/35°C treatment. The presence of these 17 compounds seemed to be influenced by the duration of exposure to these conditions. Polyphenolic compounds profiling showed the disappearance of compounds and appearance of new compounds. The disappearance of some compounds was mainly observed under extreme conditions. Antioxidant activity decreased with increasing combined CO2 concentration and temperature exposure. Antimicrobial activity showed some inhibition of S. aureus and E. coli, and the inhibition activity remained constant in all the climatic conditions. This response maybe attributed to the appearance of new polyphenolic compounds. These results suggested that C. edulis is a strong antioxidant and antimicrobial agent, owing it to the polyphenolic compounds composition. However, these properties could be negatively impacted by elevated CO2 and temperatures, thus influencing the efficacy of C. edulis. Future studies could investigate the influences of elevated CO2 and temperatures independently to assess which factor plays the biggest role in the pharmaceutical efficacy of C. edulis
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    Hold your horses: the effect of play behaviour in horses (Equus caballus) under imposed stress
    (University of the Witwatersrand, Johannesburg, 2024) Howard, Jodi Anne; Pillay, N.
    In animals, stress is inevitable, often resulting in behavioural and physiological responses to stressors. Due to the negative connotation of stress and positive connotation of play behaviour, stress and play are concepts not often coupled in research. A few studies have shown a negative association between play and stress whereas others have shown a positive association. Horses (Equus caballus), especially those in equestrian sports, are prone to acute and chronic stress. My study aimed to ascertain whether and how play behaviours can ameliorate acute stress in horses from two different stabling and working conditions (i.e. housed in a stable or on a farm). My study involved investigating the behaviours and decision- making (cognition) of the individual horses in a Y maze for a food reward. All horses were exposed to three treatments in sequence, following a repeated measures design: baseline – without a stressor; stress - exposing the horses to a short-term acoustic stressor; and play - exposing horses to a short term acoustic stressor and then initiating object play with them. Treatments were repeated twice. I recorded the behaviours of the horses and later extracted the following variables: behavioural diversity (i.e. number of behaviours displayed/total potential behaviours); frequency of behaviours (number of behaviours per 10 seconds); emotional states (positive, negative and neutral), and the time taken (latency) for the horse to make a decision in the maze. I recorded whether they made decisions at two points: 1) the decision point in the maze and 2) for a food reward located at one terminal arm of the maze; the two decisions could be uncoupled. I collected saliva from each horse before and after each treatment for later analysis of cortisol levels. I found that the horses in the stress treatment showed greater diversity and frequency of behaviours linked to a negative emotional state as well as poor decision-making compared to the play and baseline treatments. Overall, decision-making was better in the play treatment than in the baseline and stress treatments. The horses at the stable, housed under more constrained conditions were more stressed than the horses on the farm. Male horses also appeared to be more stressed compared to the female horses. Salivary cortisol was not a significant predictor of any behaviours and decision-making, nor was it predicted by treatments, stabling or sex. I found that play is able to ameliorate stress behaviourally and that it improves decision-making, which indicates that play behaviour could be a useful indicator of animal welfare. It is, however, also evident that the behavioural and physiological response to a stressor appears to be decoupled in the horses selected for study.