OpenUCT is the open access institutional repository of the University of Cape Town (UCT). It preserves and makes UCT scholarly outputs digitally and freely available, including theses and dissertations, journal articles, book chapters, technical and research reports, as well as open educational resources.
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Post-exercise ketosis
(1987) Adams, Jacob Harold; Prof. Koeslag, Johan
Koeslag, Noakes and Sloan (1980) showed that the plasma fuel-hormone concentrations during exercise, and the ketosis after exercise are critically development of dependent on the amount of carbohydrate consumed on the days preceding the exercise. This suggests that the development of post-exercise ketosis could be related to the liver glycogen content after exercise, especially since endurance training is known to hepatic glycogen increase concentrations and to provide immunity against post-exercise ketosis. As it is impractical and unethical to perform liver biopsies in healthy human subjects, it was decided to investigate the problem in an animal model.
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Open Access
The relationship between heart rate deceleration during encoding and subsequent sleep dependent emotional memory consolidation
(2025) Smith, Caitlin J; Lipinska, Gosia
Emotion and sleep are known to enhance memory, both at encoding and during the consolidation process. Furthermore, those with posttraumatic symptoms have sleep and emotional memory disruption. The interaction of emotion and sleep on subsequent recall is unclear in such a sample. This study examined the relationship between heart rate deceleration (HRD), a physiological autonomic nervous system (ANS) measure of emotion, at encoding, and subsequent sleep-dependent emotional memory consolidation. The study, based on archival data, recruited female participants, living in low-income South Africa characterised by persistent exposure to crime and violence: those with posttraumatic stress disorder (PTSD; n = 21), trauma-exposed (TE; n = 19), and healthy controls (HC; n = 20). Participants viewed highly-arousing positive or negative images and low-arousing neutral images. HRD was measured during picture presentation. Participants spent an 8-hour interval of either nocturnal sleep or daytime waking, before completing a memory recognition task to identify previously viewed images in contrast to new images. Results showed no significant differences in HRD at encoding between negative or positively valenced and neutral information, irrespective of between-group differences (HC, TE or PTSD) or condition (sleep or waking). Regarding the relationship between HRD recorded during encoding and performance on the subsequent memory task, there was an association between HRD and recall for positively valenced information rather than negative and neutral information. This association existed for those in the sleep but not the waking condition. The results suggest that psychophysiological reactivity at encoding promotes the consolidation of positive information during sleep, which may be a protective factor for this female cohort, living in an environment dominated by a high degree of negative stimuli in the form of persistent violence and crime. With regards to the group- specific associations between HRD and subsequent recognition of valenced material, there were no significant correlations in the PTSD group. TE participants had greater psychophysiological reactivity associated with better memory recognition accuracy across intervals of sleep and waking for both valenced and neutral stimuli, with some inconsistencies across sleep and wake conditions. HCs demonstrated better memory recognition with less psychophysiological reactivity for neutral information after sleep. The results tentatively suggested that in participants with PTSD, no association between HRD at encoding and memory outcomes is indicative of ANS dysregulation. In TE participants, the finding suggests that autonomic activity plays a key role in promoting memory formation, although indiscriminately of valence or sleep/waking state. In HCs, the result suggests that low physiological reactivity at encoding is necessary for remembering neutral information in those free from trauma. Concerning rapid eye movement (REM) sleep, TE participants showed this association, and there was also an association that indicated that as REM percentage increased, memory recognition accuracy for negative stimuli decreased. The results indicated a trend suggesting that as REM fragments, memory recognition accuracy for neutral stimuli decreases. These findings suggest that REM may be important for ensuring that there is a reasonable distribution of neutral and negative memory traces upon awakening, promoting resilience in the recovery from trauma. The research highlights that the relationship between HRD at encoding and subsequent memory performance is complex and requires further investigation. Future research should compare those living in high and low socio-economic contexts and control for the daily exposure to negative, positive and neutral stimuli in the environment, to better understand how both emotion and sleep contribute to memory processing.
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Open Access
Faith negotiating loyalties: an exploration of South African Christianity through a reading of the theology of H. Richard Niebuhr
(1999) Martin, Stephen William; de Gruchy, John
The context of this thesis is Christian faith in South Africa and the question of loyalties in the new, post-apartheid state. It carries out its investigation in two parts. Part one examines Christian faith and loyalty during the first nation-building exercise following the South African War, positing the creation and contestation of three Christianities corresponding to three nationalisms: South African nationalism, Afrikaner nationalism and African nationalism. Each of these nationalisms imagined South Africa in a certain way, and shaped faith accordingly. Hence the idea of South African Christianity gives way to contesting and contested Christianities, in the same way as nationalism gives way to nationalisms. Faith also emerged in tension with and in criticism of these loyalties. Part two reads H. Richard Niebuhr in South Africa. Three kinds of faith in his writings which are distinguishable in the examination of loyalties in South Africa are set forth: social faith, radical faith and reconstructing faith. The emergence of these understandings of faith in his writings is chronicled by examining five of his major writings: The Social, Sources of Denominationalism, The Kingdom of God in America, The Meaning of Revelation, Christ and Culture, and Faith on Earth. Reference is also made to Radical Monotheism and Western Culture, as well as several important transitional works in the 1930s. The interplay between radical faith and social faith is brought out, as is the idea of reconstructing faith which emerges in the 1950s. Reconstructing faith provides the link again with South Africa, and this is made apparent in an extended conclusion to chapter nine which is also a resume of the exposition of Niebuhr's works, and in the conclusion to the thesis. The self and the society is not the unity that Niebuhr held, but rather is constituted by hybridities and suspended in a web of loyalties. The message for faith in a post-apartheid South Africa that this reading suggests is the importance of negotiating covenants which allow for crossings, hybridities and contestations. Hence the title of this thesis: faith negotiating loyalties.
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Open Access
Genome size variation in Cape schoenoid sedges & amp; its ecophysiological consequences
(2023) Van Mazijk, Ruan; Muasya, Muthama; Verboom, Anthony; West, Adam
Understanding the e ects of genome size on the phenotype is a major endeavour in evolutionary studies. Larger genome size is associated with larger cells. In plants, this is evident in stomatal guard cells, which are less water-use e cient (WUE) when large. Furthermore, stomatal size and density are important aspects of plant ecophysiology pertaining to water-balance. Thus, genome size could covary with aspects of plant function. Variation in genome size across plants is often due to polyploidy. This is known to have occurred multiple times in the austral sedge genus Schoenus L. (Cyperaceae: Schoeneae), with a richness-centre (ca. 45 spp.) in the Cape Floristic Region (CFR). The other major schoenoid genus in the CFR is Tetraria P.Beauv. (ca. 40 spp.), exhibiting smaller genomes similar to the majority of Cyperaceae. Comparing these genera, the two most species-rich genera of Cape schoenoid sedge, is useful, as they co-occur in fynbos landscapes, subject to similar broad bioclimatic conditions. I hypothesise that CFR Schoenus species to be more WUE, as a function of lower maximum stomatal conductance (gwmax) imposed by larger, less dense stomata. I also expect genome size to a ect stomatal parameters uniformly across plants' organs, with further functional di erences between the genera (e.g. cauline leaves in Tetraria) manifesting in other traits (e.g. C:N ratios). To test this, I investigate relationships between genome size and stomatal parameters in a phylogenetic context, after reconstructing a dated tree for CFR occurring Schoeneae. With the aid of scanning electron microscopy (SEM), species' stomatal and whole plant trait data were measured from field collections and herbarium specimens. Carbon stable isotopes (”13C) were also measured as an index of WUE. Following linear and phylogenetically generalised analyses of this species level dataset, the Schoenus exhibit less phylogenetic structure in genome size (K = 0.59, ⁄ =0.34) than Tetraria (K = 0.97, ⁄ = 0.76). This is congruent with more frequent polyploidisation in Schoenus causing sister lineages to have necessarily dissimilar genome sizes. As expected, phylogenetically generalised least squares (PGLS) regressions demonstrated that guard cell length and stomatal density (themselves negatively dependent) both covary with genome size, positively and negatively respectively, with genome size explaining 72–75% of the variation in guard cell length. Additionally, gwmax and C:N were lower in larger-genomed species, particularly in culms (with larger, low-density guard cells). The former suggests a nities for arid habitats in CFR Schoenus, although these species' relatively wide viii f lowering intervals point to variation in climatic a nities across species' ranges. Though ”13C did not vary significantly with genome size, it was lower in culms than in leaves, across species (phylogenetic paired t-test: P < 0.001). Additionally, I suggest that the di erences in vegetative morphology and C:N between the genera are evidence of more conservative, e cient ecophysiological strategies in CFR Schoenus compared to more acquisitive strategies in Tetraria. As Schoenus species have smaller, often reduced leaves compared to Tetraria species, they likely rely more on culm photosynthesis. Summarily, trait vs genome size and trait vs trait relationships across the CFR Schoeneae confirms how ecophysiology correlates with genome size, though confounding sources of trait variation (e.g. frequent polyploidy and putative allopolyploidy in Schoenus) limit inferences about causal links between the nucleotype and any given trait.
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Open Access
From proteomics to biotechnology. using the resurrection plant eragrostis nindensis to genetically engineer drought tolerant crops
(2023) Van Der Pas, Llewelyn; Farrant, Jill; Hilhorst, Henk; Hitzeroth, Inga; Rafudeen, Suhail
Global climate change is increasingly putting pressure on finding innovative solutions to ensure future food security in particular to developing African nations. Of great relevance are regionally adapted crops, known as orphan crops, which tend to have very little economic value but can provide a source of alternative food security. Vegetative desiccation tolerance is a remarkable feat of selective evolution and is only present in a small number of angiosperms. The ability of some plants, such as Eragrostis nindensis to survive complete cellular water deficit provides an attractive model for discovery-based omics to not only understand the mechanisms involved in driving desiccation tolerance but to explore the feasibility of potential target genes for orphan crop improvement. The work presented herein was aimed at complementing a transcriptomic study using the same leaf tissue from that study to evaluate the changes from RNA to protein and to determine whether there were proteomic signatures that could differentiate the desiccation-tolerant non-senescent (NST) leaves from the desiccation-sensitive senescent (ST) leaves. The data presented here illustrate that several important metabolic pathways are significantly reprogrammed, that only a small subset of proteomic-matching transcripts were translated, and that proteomic differences between the NST and ST were noted despite their being significant similarities between the two in general oxidative and osmotic stress. For instance, the prevention of ferroptosis and accumulation of raffinose synthase and starch synthase in the NST exclusively illustrated that small and subtle increases in protein abundance are likely responsible for enabling resurrection in the NST and not in the ST, which we hypothesise here is likely due to sacrificing of ST upon rehydration as a means to act as a source of nutrition for the NST during resurrection. The study also focussed on functional characterisation of a heat shock 70 protein from E. nindensis as a target for genetic engineering. The selected EnHSP70 was shown to localise to the chloroplast and was able to undergo liquid-liquid phase separation in vitro in a protein concentration and polyethylene glycol dependent manner which could have broad impacts on its role in maintaining proteostasis. In Arabidopsis thaliana, overexpression of EnHSP70 resulted in a stunted germination phenotype whereas expression in BL21 Escherichia coli did not enhance tolerance towards salt or mannitol stress. Furthermore, incubation of EnHSP70 with lactate dehydrogenase did not confer improved thermotolerance. Taken together, the selected HSP70 from E. nindensis did not appear to be involved in stress response and is likely involved with general proteostasis. Lastly, a method for generating embryonic calli from Eragrostis tef is presented with the goal of using this developed protocol for the genetic improvement of the Ethiopian orphan crop.