Browsing by Subject "Molecular and Cellular Biology"

Now showing 1 - 11 of 11
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    Characterisation of the AT4G11100 gene, a negative regulator of disease resistance in Arabidopsis thaliana
    (2015) McCrindle, Tyronne K; Ingle, Robert A
    Plants have evolved a complex system of defence to prevent pathogen establishment. The Arabidopsis thaliana cir1 (constitutively induced resistance 1) mutant displays enhanced resistance to infection by the virulent bacterial pathogen Pseudomonas syringae and constitutively expresses a number of defence genes. Evidence suggests that CIR1 is a negative regulator of plant immunity important in the absence of pathogen attack. Genetic mapping experiments indicate that cir1 is located on the lower arm of chromosome 4 of A. thaliana and may be one of 8 known genes in the region. Analysis of T-DNA knockouts of these 8 genes suggests that AT4G11100 is the mostly likely candidate for CIR1. This project established that the disease resistance phenotype of cir1 is temperature dependent and linked to reduced plant growth. Genetic crosses between cir1 and at4g11100 T-DNA knockout mutants revealed that the mutants complement and therefore AT4G11100 is not CIR1. However, like cir1, the at4g11100 T-DNA knockout mutants display enhanced disease resistance. Over expression of AT4G11100 leads to increased susceptibility to infection by Pseudomonas syringae (Pst) and reduced induction of the salicylic acid defence gene PR2 following Pst infection, suggesting that AT4G11100 may too be a negative regulator of immunity. Additionally, a plant line with exceptionally high AT4G11100 expression levels displayed distinct leaf morphology, possibly implicating AT4G11100 in leaf development.
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    Characterisation of the role of brain factor 1 in the olfactory neuroepithelium during neuronal development
    (2003) Linda, Pride; Illing, Nicola; Patterton, Hugh
    Brain Factor 1 (BF-1), a winged helix transcription factor, displays a restricted pattern of expression within the developing forebrain, playing a critical function in the regulation of neuronal progenitor cell proliferation and differentiation within the developing forebrain. The molecular mechanisms by which BF-1 carries out its function remain to be elucidated. Hence, this study aimed to investigate and characterise the molecular mechanisms by which BF-1 function is regulated during neuronal development.
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    Characterization of polyphenols in leaves of four desiccation tolerant plant families
    (2005) Dzobo, Kevin; Lindsey, George G; Farrant, Jill M; De Wet, Jacques
    Polyphenols in plants are known to act as antioxidants, antimicrobials, antifungal, photoreceptors, visual attractors and as light screens. In this study polyphenols in angiosperms found in southern Africa and called resurrection (desiccation tolerant) plants were studied. These plants are Myrothamnus flabellifolius, Xerophyta viscosa, Xerophyta humilis, Xerophyta schlecterii, Xerophyta villosa. Craterostigma wilmsii, Craterostigma plantagineum, Craterostigma pumilum and Eragrostis nindensis. These plants are able to tolerate water stress without undergoing permanent damage. During drying these plants are subjected to different stresses and one such stress is oxidative stress. It has been suggested that polyphenols function as stress protectants in plant cells by scavenging reactive oxygen species (ROS) produced during a period of oxidative stress. In this study the total phenolic content and the related antioxidant capacity of the plants leaf extracts were analysed.
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    Development of a Dusky kob scFv gene phage display library for the discovery of antibodies to Brome mosaic virus - a proxy for a novel, emerging fish pathogen
    (2021) Naylor, Kyle Andrew; Coyne, Vernon
    Fish farming is rapidly becoming the world's fastest growing production sector, achieving an annual growth rate of approximately 8.9% since the early 1970s. However, high stocking densities result in elevated stress levels in farmed fish, leading to increased susceptibility to infection by opportunistic pathogens and parasites. Antibody phage display is a method that allows foreign peptides or proteins to be expressed on the phage surface through translational fusion with phage coat proteins. Consequently, antibodies expressed by a diverse repertoire of genes coding for the single chain variable fragment (scFv) of immunoglobulin M can be isolated and screened for affinity to a specific infectious agent or parasite. In this study, a phage display library displaying scFvs derived from combination pairings of Dusky kob (Argyrosomus japonicas) variable heavy and light chain fragments, sourced from the splenic B cells of healthy Dusky kob, was constructed. The library was subjected to two rounds of biopanning against brome mosaic virus (BMV), a grass virus to which Dusky kob would have no prior exposure that served as a proxy for an emerging fish pathogen. Five clones were identified as having high affinity and specificity to BMV, as determined by phage enzymelinked immunosorbent assay (ELISA) and phage western blot analysis, respectively. To validate the diagnostic and therapeutic potential of antibody fragments isolated from this phage display library, the gene encoding the antibody fragment of the clone displaying the highest affinity to BMV was selected and expressed using a yeast surface display system. ELISA analysis of serum sampled from Dusky kob exposed to BMV by injection demonstrated that the yeast displayed anti-BMV antibody could successfully detect BMV in the blood serum of BMV-infected Dusky kob with similar sensitivity to a commercially available counterpart. Similarly, this study demonstrated the neutralising effect of yeast displayed anti-BMV antibodies which were found to successfully reduce BMV infection in barley. Overall, these findings demonstrate the feasibility of a Dusky kob phage display library as a source of diagnostically and therapeutically important antibodies against emerging fish pathogens or parasites that threaten the fish farming industry of South Africa.
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    Genetic effects of prolonged UV-B exposure in a Namaqualand daisy - Dimorphotheca sinuata
    (2001) Mpoloka, Sununguko Wata; Thomson, Jennifer Ann; Abratt, Valerie Rose; Mundree, Sagadevan G; Riddoch, Bruce
    This thesis describes investigations into the genetic effects of long term UV-B exposure in Namaqualand daisies (Dimorphotheea sinuata) grown for several generations under ambient and enhanced UV-B levels. Enhanced UV-B radiation was found to have a major effect on the biochemical composition of the chloroplast accompanied by impairment of photosynthetic function, involving a down-regulation of photosynthetic genes and an up-regulation of flavonoid biosynthesis.
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    Identification of the cir1 disease resistance gene in Arabidopsis thaliana
    (2012) Diener, Anastashia; Ingle, Robert
    Plants rely on an elaborate multi-layered defence system to perceive and effectively respond to disease causing pathogens. The defence-related cir1 (constitutively induced resistance 1) mutant was first isolated in an effort to identify components of the Arabidopsis thaliana defence system essential for resistance against pathogens. The cir1 mutant has previously been described as having increased resistance to the virulent bacterial pathogen Pseudomonas syringae pv. tomato DC3000 and oomycete pathogen Hyaloperonospora parasitica Noco2 and was shown to constitutively express salicyclic acid-, jasmonic acid/ethylene- and reactive oxygen intermediate-responsive genes. Genetic analysis and mapping studies of the mutation revealed that it is recessive and may be encoded by one of eight genes located within a 309.10 kb region on the lower arm of chromosome four.
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    An investigation of the sociogenetic structure of the endemic fynbos ant, Camponotus klugii, via the use of microsatellites
    (2008) Muna, Natashia; O'Ryan, Colleen
    Eusocial insects, in particular ants, demonstrate great variability in their sociogenetic structure with regards to colony organization, queen number, queen mating frequency, levels of relatedness and worker reproduction. Within this study I perform an analysis on two groups of ant nests of the species Campo notus klugii, in order to investigate how the genetic structure may inform us of the sociogenetic structure of the species.
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    The isolation and characterization of heat shock protein Hsp12 in Lipomyces starkeyi
    (2002) Mukwevho, Emmanuel; Brandt, Wolf F; Lindsey, George G
    The stress response protein Hsp 12 is induced in S. cerevisiae cells upon exposure to salt stress, heat shock, ethanol, and upon entry to stationary phase (Mtwisha et aI., 1998). In this study, the occurrence of proteins related to Hsp12 was investigated in a number of yeasts (namely, Saccharomyces cerevisiae S288C, Schizosaccharomyces pombe, Debaromyces hansenii, Lipomyces starkeyi Y-2024, Saccharomyces cerevisiae IFO 23X7 (Kaokai), Zygosaccharomyces rouxii and Pichia sorbitophila. This was performed by selective protein extraction followed by SDS-P AGE and western blotting using a S. cerevisiae anti-Hsp 12 antibody. The results showed that almost all the yeasts investigated possessed a protein that had an identical migration to that of Hsp 12 with the exception of S. pombe, which contained a 9 kDa protein. Western blotting using the antiHsp 12 antibody cross-reacted only with the two S. cerevisiae species in addition to the 12 kDa protein from Lipomyces starkeyi of all the species investigated. MALDI-TOF peptide mass analysis after tryptic digestion of the L. starkeyi 12 kDa protein showed that a close sequence similarity existed to that of S. cerevisiae Hsp 12 and none to rest of the 12 kDa proteins isolated from all the other species investigated. In order to determine the sequence of the Hsp 12 protein, the L. starkeyi Hsp 12 gene was amplified using S. cerevisiae Hsp 12 primers. Gene sequencing of both S. cerevisiae and L. starkeyi Hsp 12 genes revealed three nucleotide differences existed between them. L. starkeyi Hsp 12 was found to be present in relatively small amounts during early growth stages but increased during log phase with a slight further increase during stationary phase. Increasing the salt concentration in the growth medium was found to induce Hsp 12. Increased levels of Hsp 12 appeared to confer a degree of protection during desiccation and subsequent rehydration of both L. starkeyi and S. cerevisiae.
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    Nutraceutical antioxidant potential and polyphenolic profiles of the Zambian market classes of bambara groundnuts (Vigna subterranea L. Verdc) and common beans (Phaseolus vulgaris L.)
    (2013) Nyau, Vincent; Farrant, Jill M; Rodriques, Jerry; Prakash, Shiv
    There is a growing interest in legumes and legume based foods because of the health claims associated with their consumption. The aim of the current study was to explore the nutraceutical potential of bambara groundnuts (Vigna subterranea L. Verdc) and common beans (Phaseolus vulgaris L.) commonly grown in Zambia based on the antioxidant properties and phenolic phytochemical profiles. Two market classes of bambara groundnuts (red and brown) and four of common beans (red, grey mottled, brown and white) were screened in raw dry form. Effects of cooking and sprouting on the antioxidant activities and phenolic phytochemicals of the promising market classes were assessed. The study employed in vitro antioxidant assays (DPPH and FRAP) to screen for antioxidant properties, HPLC-PDA-ESI-MS and Folin Ciocalteu assay to screen for phenolic phytochemical profiles.
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    Studies on carbohydrate metabolism in Bifidobacterium : isolation, characterisation and regulation of a sucrose-utilisation gene cluster in Bifidobacterium lactis
    (2002) Trindade, Marla; Abratt, Valerie Rose; Reid, Sharon J
    The primary aim of the project was, therefore, to analyse carbohydrate metabolism for the identification of and/or the development of prebiotic substrates, and to provide a molecular characterisation for their utilisation. Several carbohydrates were tested for their ability to support the growth of bifidobacteria as a sole carbohydrate source. The four bifidobacterial strains, B. breve, B. bifidum, B. longum and B. lactis were able to utilise a wide variety of substrates.