Browsing by Author "Jooste, Michelle"
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- ItemDiversity and nature of microbial endophytes associated with southern African Oxalis(Stellenbosch : Stellenbosch University, 2019-03) Jooste, Michelle; Dreyer, L. L.; Midgley, Guy F.; Oberlander, Kenneth C.ENGLISH ABSTRACT: Symbioses between plants and micro-organisms have profound influences on biodiversity, ecosystem structure and functioning and patterns of evolution. The Greater Cape Floristic Region (Cape) of southern Africa is global biodiversity hotspot, and is renowned for its diverse and extremely rich flora. At least some of this remarkable diversity has been attributed to abiotic factors such as palaeoclimatic stability, reliable seasonal water availability, geographical gradients and diverse soil types. Cape soils contain some of the lowest nitrogen and phosphorus levels measured globally though, and these may be limiting factors in plant growth. Despite the obvious importance of plant microbial endophytes, the role of such associations in generating and maintaining plant diversity has largely been neglected to date. The Cape is also renowned for the most diverse geophyte flora in the world, including 2100 species from 20 families. Despite this, the role of plant-microbial interactions has not yet been confirmed in any Cape geophyte lineage. Cape Oxalis (Oxalidaceae) is recognised as the sixth largest plant lineage and the largest geophytic genus in the Cape. Although widespread in southern Africa, Oxalis has undergone extensive radiation in the Cape and currently includes more than 200 known species. Members occur across a vast range of environments, but are well-represented in the nutrient poor and/or drought prone habitats of the Cape. The evolutionary success of this genus in the Cape may partly be attributed to various unique life history traits (geophytic habit, winter flowering, variable seed strategies), but this is still poorly understood. Cape Oxalis species are highly unusual in terms of their seed germination strategies. Although dormant seeds represent the ancestral state in Oxalis, approximately 60% of the lineage has exendospermous seeds that lack a dormancy period, a mechanism known as recalcitrance. The morphological gulf between these strategies (and potential intermediate morphologies) has been poorly quantified, with questions regarding their ecological function and evolution still unanswered. I hypothesized that the binary classification of seed germination strategies (dormancy and recalcitrance) oversimplifies seed physiology and morphology of Cape Oxalis. Here I identified three physiological germination strategies (supported by morphology and phenology), in a system where the ancestral dormant state has evolved towards a maximally recalcitrant peak among Cape Oxalis. Additionally, a mosaic of intermediate character states is reflected in extant taxa. Recalcitrance and intermediate germination strategies are rare among angiosperms (11% of species). Insights gained from studying Cape Oxalis as an ideal model system has promoted our understanding of the evolution of the recalcitrant germination strategy, among Oxalis and angiosperms in general. Recalcitrant and some intermediate Oxalis seeds are metabolically active when shed, which enables them to germinate, establish and reach maturity much more rapidly than dormant seeds. The majority of these recalcitrant species also display a strategy of inverse germination relative to other angiosperm seedlings, where cotyledons and the first foliar leaf develop rapidly, relative to the hypocotyl, root hairs and roots that subsequently emerge. This is a remarkable phenomenon where seedlings are capable of rapid growth and development temporarily, without well-established roots to supply the seedling with nutrients. Furthermore, 70% of the recalcitrant Oxalis species (and a few intermediate species) produce large amounts of (often acidic) mucilage around the base of the hypocotyl of seedlings. The mucilage secreted by developing recalcitrant seedlings could both include growth promoting endophytes and serve as a potential attractant to plant growth promoting micro-organisms from the soil environment. As a first step towards exploring the inter-organismal associations of Cape Oxalis, I thus studied intra-plant, intra- and inter-species, and inter-site microbe richness and community composition of rhizosphere and endosphere microbes associated with Oxalis hosts. Overall, 46 culturable bacterial and 39 culturable fungal morphotypes were associated with host plants (regardless of seed germination strategy). The endophytic microbial richness and composition changed according to the surrounding environment. The most common and frequently encountered bacterial endophytes included members from the genus Bacillus Cohn - a group well-known for various plant-growth promoting properties. A surprisingly diverse collection of bacterial and fungal endophytes was also commonly found in the reproductive and vegetative propagules of all hosts. Next culture-independent 16S metabarcoding was conducted to document non-culturable bacterial endophytes associated with Oxalis. Despite various caveats associated with this approach, significant insights into the diversity of bacterial endosymbionts associated with Cape Oxalis host plants were gained. Putative genus-level identification revealed bacterial taxa from 118 genera, as well as various uncultured bacteria, which collectively belong to 79 families, 39 orders and 19 classes from eight bacterial phyla. Metabarcoding results confirmed the presence of six out of nine bacterial genera identified with culture-dependent techniques. Even though bacterial endophyte species identities could not yet be confirmed, the majority of these genera include various well-known plant endophytes with strong growth promoting and nitrogen-fixing abilities. Filter exclusion experiments were conducted to determine if endophytes were vertically-transmitted to seeds, determine if mucilage plays a role to actively attract microbes from the soil and to assess microbial richness isolated from the mucilage of Oxalis seedlings. Fluorescent microscopy was implemented in order to visualize endophytic bacteria in cryo-sectioned seeds. I report evidence for a novel, vertically transmitted symbiosis between communities of nitrogen-fixing and plant growth-promoting Bacillus endophytes and selected Oxalis hosts. Three common nitrogen-fixing Bacillus species have known oxalotrophic properties and appear to be housed inside specialised cavities (containing oxalates) within the plant body and seeds. The discovery of vertical transmission and potential benefits to both host and endophyte suggest a particularly tight mutualism in the Oxalis-endophyte system. This discovery suggests unexpected ways in which these geophytes might avoid nitrogen deficiency, and suggest that vertically-inherited mutualisms could be impacting plant survival in nutrient-depleted environments such as the Cape. Knowledge of vertical transmission of nitrogen-fixing and oxalotrophic bacteria among angiosperms may have far-reaching conservation, agricultural and economic applications.
- ItemNitrogen-fixing bacteria and Oxalis – evidence for a vertically inherited bacterial symbiosis(BMC (part of Springer Nature), 2019-10-23) Jooste, Michelle; Roets, Francois; Midgley, Guy F.; Oberlander, Kenneth C.; Dreyer, Leanne L.Background: Plant-endophyte symbioses often revolve around nitrogen metabolism, and involve varying degrees of intimacy. Although evidence for vertical inheritance of nitrogen-fixing endophytic bacteria is increasing, it is confined mostly to crop plants, and to date no such system has been reported for geophytes. Methods: Bacterial endophytes associated with Oxalis, the most species-rich geophytic genus form the Cape Flora in southern Africa was studied. Culturable endophytes were isolated from surface-sterilized vegetative and reproductive plant organs for six host species at three locations. Colonies of microbes on various artificial media were morphotyped, enumerated and identified using sequence data. Filter exclusion experiments were conducted to determine if endophytes were vertically transmitted to seeds, determine if mucilage plays a role to actively attract microbes from the soil and to assess microbial richness isolated from the mucilage of Oxalis seedlings. Fluorescent microscopy was implemented in order to visualize endophytic bacteria in cryo-sectioned seeds. Results: Evidence for a novel, vertically transmitted symbiosis was reported. Communities of nitrogen-fixing and plant growth-promoting Bacillus endophytes were found to associate with selected Oxalis hosts from nitrogen-deficient environments of the Cape. Bacillus endophytes were ubiquitous and diverse across species and plant bodies, and were prominent in seeds. Three common nitrogen-fixing Bacillus have known oxalotrophic properties and appear to be housed inside specialised cavities (containing oxalates) within the plant body and seeds. Conclusions: The discovery of vertical transmission and potential benefits to both host and endophyte suggest a particularly tight mutualism in the Oxalis-endophyte system. This discovery suggests unexpected ways in which geophytes might avoid nitrogen deficiency, and suggest that such symbioses are more common than previously expected.
- ItemOxalis seeds from the Cape Flora have a spectrum of germination strategies(Botanical Society of America, 2019) Jooste, Michelle; Midgley, Guy F.; Oberlander, Kenneth C.; Dreyer, Leanne L.PREMISE OF THE STUDY: Seed germination strategy has profound ecological and evolutionary consequences, with transitions between germination strategies receiving renewed recent attention. Oxalis from the Cape Flora, South Africa, has seeds with two contrasting germination strategies: orthodox and recalcitrant. The morphological gulf between these strategies (and potential intermediate morphologies) has been poorly quantified, with questions regarding their ecological function and evolution. We reconsidered this binary classification, emphasizing potential intermediate states. METHODS: Seed physiological traits were used to assign strategies to 64 Oxalis species. We tested for morphological/phenological signal corresponding to defined strategies with cluster, principal component, Kmeans clustering and discriminant analyses. KEY RESULTS: We show that an intermediate germination strategy does exist among Cape Oxalis, with two possible morphological groups within each strategy. These could reflect a continuum of germination states, where an ancestral orthodox strategy evolved towards a maximally recalcitrant peak, with a mosaic of intermediate states reflected in extant taxa. CONCLUSIONS: Environmental factors may affect germination strategy and distribution throughout the Cape because recalcitrant and intermediate species are confined to the winter rainfall region. They occupy specialized niches and may face adverse impacts under predicted climate change (hotter and drier winters), meriting focused future conservation.
- ItemThe phylogenetic and potential functional significance of leaf anatomical and physiological traits of southern African Oxalis(Stellenbosch : Stellenbosch University, 2016-03) Jooste, Michelle; Dreyer, L. L.; Oberlander, K. C.; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.ENGLISH ABSTRACT: The southern African Oxalis radiation is extremely morphologically variable and few characters are known as synapomorphies supporting DNA-based clades, hindering species identification, taxonomic revision and understanding of functional trait evolution in this clade. Sixty-eight leaflet anatomical traits of 109 southern African Oxalis species were assessed in search of phylogenetically significant characters that delineate clades. This study showed that the combination of six leaflet anatomical traits (stomatal position, adaxial epidermal cell types, abaxial epidermal cell types, mesophyll type, sheath around vascular tissue and degree of leaflet conduplication) clearly support various clades de ned by previous DNA-based phylogenetic work. Despite the phylogenetic patterns detected in the aforementioned traits, other leaflet anatomical traits were highly variable and showed no phylogenetic pattern: these traits could possibly hold functional significance. The information gathered in this study will aid in the taxonomic revision of this speciose member of the Greater Cape Floristic Region (GCFR) and provide a basis for future hypotheses regarding its radiation. Limited previous work on Oxalis has shown evidence for CAM photosynthesis in some South American species and preliminary anatomical work on southern African Oxalis hinted at Kranz anatomy, typically associated with C4 photosynthesis. We assessed stable carbon-isotope data, stomatal conductance and anatomical traits for 67 southern African Oxalis species to test whether any indigenous species show alternative modes of photosynthesis. All assessed taxa followed an exclusively C3 photosynthetic pathway. The measured stomatal conductance data of southern African Oxalis species showed that many species make minimal effort to prevent water loss, even though Oxalis was previously regarded as a water-conservative genus (Kluge and Ting (1978); Proches et al. (2006a); Biocyclopedia: Oxalis (2012)). Additionally we observed that the majority of southern African Oxalis species have epistomatic leaflets, which is regarded as the rarest stomatal position among all angiosperms. Interestingly, epistomatic leaflets had significantly smaller stomata (which enables fast response to changes in environmental conditions) and significantly higher conductance rates (which enables carbon fixation to take place at a faster rate). We propose that this strategy would be favoured under the strongly seasonal environment in which the majority of southern Africa Oxalis grows (winter rainfall Mediterranean climate), as this enables these plants to take advantage of their growing conditions to ensure high productivity, rapid growth and successful carbon storage into their below-ground organs. We propose that the strategy of small adaxially-located stomata with high conductance rates might be an overlooked key innovation driving diversification into one of the largest geophytic plant lineages within the GCFR.
- ItemThe phylogenetic significance of leaf anatomical traits of southern African oxalis(BioMed Central, 2016-10) Jooste, Michelle; Dreyer, Leanne L.; Oberlander, Kenneth C.Background: The southern African Oxalis radiation is extremely morphologically variable. Despite recent progress in the phylogenetics of the genus, there are few morphological synapomorphies supporting DNA-based clades. Leaflet anatomy can provide an understudied and potentially valuable source of information on the evolutionary history and systematics of this lineage. Fifty-nine leaflet anatomical traits of 109 southern African Oxalis species were assessed in search of phylogenetically significant characters that delineate clades. Results: A combination of 6 leaflet anatomical traits (stomatal position, adaxial epidermal cells, abaxial epidermal cells, mesophyll, sheath around vascular tissue, degree of leaflet conduplication) clearly support various clades defined by previous DNA-based phylogenetic work. Other, mostly continuous leaflet anatomical traits were highly variable and showed less phylogenetic pattern. Conclusions: Major and unexpected findings include the transition from ancestral hypostomatic leaflets to adaxially-located stomata in the vast majority of southern African Oxalis, the loss of semi-swollen AB epidermal cells and the gain of swollen adaxial and abaxial epidermal cells in selected clades, and multiple changes from ancestral bifacial mesophyll to isobilateral or homogenous mesophyll types. The information gathered in this study will aid in the taxonomic revision of this speciose member of the Greater Cape Floristic Region and provide a basis for future hypotheses regarding its radiation.
- ItemThe prevalence, knowledge and reasons for carbohydrate, protein, creatine and glutamine use among first team rugby players in premier rugby schools in the Western Cape Province(Stellenbosch : Stellenbosch University, 2016-12) Jooste, Michelle; Potgieter, Sunita; Havemann-Nel, Lize; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Global Health. Human Nutrition.ENGLISH SUMMARY : Background: Nutrition plays an important role in optimal athletic performance as “strengthand-power athletes” like rugby players would go to great lengths to increase their impact in this competitive environment. As a result, additional nutritional strategies are adopted. However, the potential adverse effects of such strategies on their health and the impact of these strategies on moral development are unclear. Healthcare professionals are concerned about the performance-enhancing supplements that young athletes are using. Research methodology: This cross-sectional study design used a self-administered questionnaire which consisted of specific questions to determine the prevalence and knowledge of and reasons for carbohydrate, protein, creatine and glutamine use among adolescent rugby players. Participants consisted of 189 rugby players from four League A and six League B rugby schools in the Western Cape, including 18 of their coaches. Results: The majority of players used carbohydrates (92%) followed by protein (79%) while only 37% of the players reported using creatine and glutamine. The prevalence of protein and glutamine use among League A players was significantly higher compared to League B players (90% vs. 69%, p<0.001 and 59% vs. 17%, p<0.001 for protein and glutamine respectively). The overall knowledge scores were poor (43%) with League A players performing significantly better than League B players (48% vs. 39%, p<0.001). Knowledge regarding the role of glutamine supplementation in particular was very poor. The majority of players indicated that they need education regarding supplementation and that they have not consulted a dietitian on diet and supplement use. The main reported reason for using carbohydrate supplements was to reduce fatigue/increase energy (46%) followed by an increase in muscle mass/strength (29%). Protein is reportedly consumed firstly to increase muscle mass/strength (72%) and secondly to enhance muscle recovery (24%). Creatine is predominantly used to increase muscle mass/strength while glutamine is reportedly used to enhance muscle recovery. The main source of supplement information is the coach (28%), followed by the trainer (19%) and the supplement representative (16%). Only a few of the players were aware of the amount of carbohydrates (4%), protein (22%), creatine (13%) and glutamine (4%) supplements they consumed on a daily or weekly basis with the exception of the 29% of League B players who were aware of the dose of protein they were consuming. Discussion: The majority of the rugby players in this study used CHO, followed by protein supplements, with fewer using creatine and glutamine. It was evident from the findings of this study that knowledge about safe and appropriate supplement use is currently lacking in both League A and League B rugby schools in the Western Cape. The main reasons why these rugby players use supplements are to increase energy or reduce fatigue, to increase muscle mass and to assist with muscle recovery. According to these rugby players, carbohydrates will assist to increase energy/reduce fatigue and, similar to protein, increase muscle mass and assist with recovery. There is a misconception regarding the reasons for creatine and glutamine use. Additionally, the minority of the athletes were aware of the amount of supplements they consumed on a daily or weekly basis. Athletes looked to coaches and trainers for nutritional information, while these coaches and trainers also lacked supplement knowledge. Developing an educational programme for coaches, athletes and all involved in high school rugby, based on the latest scientific research, would benefit schools and athletes.