Browsing by Author "Bentley, Joanne"
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- ItemRestrictedComparative metabolomic profiling of phenolics in the desiccation-tolerant “resurrection plant” Myrothamnus flabellifolia (Myrothamnaceae) using conventional and green chemistry-based solvent systems(2019) Bentley, Joanne; Verboom, TonyMyrothamnus flabellifolia (Myrothamnaceae) belongs to a group of ±300 angiosperm species known as “resurrection plants” that exhibit vegetative desiccation tolerance. They are able to survive dehydration to an air-dry state, tolerating up to 95% cellular water loss for a prolonged period of time followed by the rapid recovery of metabolism in the tissues within 24–72 h of rehydration. Prolonged cellular water loss is deleterious and is associated with the production of reactive oxygen species (ROS), which causes cellular degeneration, and ultimately, death. Resurrection plants have evolved various strategies to ameliorate this damage, including biochemical, ultrastructural, and anatomical modifications. Myrothamnus flabellifolia is widespread across southern Africa, and within its range it occurs in regions that experience high, moderate, and low rainfall; the low rainfall region also being associated with longer dry periods. Myrothamnus flabellifolia has historically been used for the treatment of chest infections, uterine pain, and gingivitis, and, more recently, has been shown to exhibit various phytochemical activities relating to the potential inhibition of diabetes, reverse transcriptases, and microbes. Previous studies have found M. flabellifolia extracts to contain high levels of polyphenolic compounds, which act as protectants against the ROS-induced damages caused by prolonged periods without moisture. However, a global assessment of the phenolic constituents, including anthocyanins, present in M. flabellifolia from across its geographic range is currently lacking. As the biosynthesis of compounds is likely to be subject to a fair amount of environmental control, an evaluation of the molecules present in this species from across its geographic range is warranted. Thus, in this study, a liquid chromatography-tandem mass spectrometry (LC-MS/MS) metabolomics approach was used to screen for phenolic compounds, including anthocyanins, from leaf material sampled in the field from eight populations representing the western, southern, and eastern range of the species distribution. Putative phenolic compounds were identified based on their MSE spectra in the negative ionisation and positive ionisation (for anthocyanins) modes. Their potential roles in the ROS-scavenging capacity of this plant were also discussed. Using this information, multivariate statistics were used to compare the phenolic profiles of the different populations in order to ascertain whether plants from the different regions were associated with any particular phenolic signature, and this was also evaluated against a phylogenetic hypothesis for species relationships based on three non-coding chloroplastic markers. Additionally, a preliminary green chemistry-based extraction protocol using Natural Deep Eutectic Solvents was also used to further screen for phenolic compounds, and this was compared against the conventional organic solvent system. Several phenolic compounds not previously detected in M. flabellifolia were putatively identified, many of which, based on an assessment of the literature, are associated with high antioxidant activity. The phylogenetic analyses suggested that the Namibian plants are more highly diverged than the South African and Malawian plants. The metabolomics analysis corroborated the DNA analysis, in that the most differentially expressed ions in the Namibian population were able to discriminate these samples from both the Malawian and South African samples. While the phenolic profiles of the samples collected from the same countries were similar, there was reasonable withinpopulation variability in those collected from South Africa and Malawi. Conversely, the Namibian samples exhibited far less variability, suggesting that a particular suite of protective compounds may be required for survival in that comparatively drier region. A Natural Deep Eutectic Solvent-based system successfully targeted phenolics in M. flabellifolia and thus constitutes a potential future green chemistry solution for phytochemical investigations in medicinal plants.
- ItemOpen AccessErosive processes after tectonic uplift stimulate vicariant and adaptive speciation: evolution in an Afrotemperate-endemic paper daisy genus(BioMed Central, 2014-02-13) Bentley, Joanne; Verboom, G A; Bergh, Nicola GBackground: The role of tectonic uplift in stimulating speciation in South Africa’s only alpine zone, the Drakensberg, has not been explicitly examined. Tectonic processes may influence speciation both through the creation of novel habitats and by physically isolating plant populations. We use the Afrotemperate endemic daisy genus Macowania to explore the timing and mode (geographic versus adaptive) of speciation in this region. Between sister species pairs we expect high morphological divergence where speciation has happened in sympatry (adaptive) while with geographic (vicariant) speciation we may expect to find less morphological divergence and a greater degree of allopatry. A dated molecular phylogenetic hypothesis for Macowania elucidates species’ relationships and is used to address the potential impact of uplift on diversification. Morphological divergence of a small sample of reproductive and vegetative characters, used as a proxy for adaptive divergence, is measured against species’ range distributions to estimate mode of speciation across two subclades in the genus. Results: The Macowania crown age is consistent with the hypothesis of post-uplift diversification, and we find evidence for both vicariant and adaptive speciation between the two subclades within Macowania. Both subclades exhibit strong signals of range allopatry, suggesting that geographic isolation was important in speciation. One subclade, associated with dry, rocky environments at high altitudes, shows very little morphological and ecological differentiation but high range allopatry. The other subclade occupies a greater variety of habitats and exhibits far greater morphological differentiation, but contains species with overlapping distribution ranges. Conclusions: Species in Macowania are likely to have diversified in response to tectonic uplift, and we invoke uplift and uplift-mediated erosion as the main drivers of speciation. The greater relative morphological divergence in sympatric species of Macowania indicates that speciation in the non-sympatric taxa may not have required obvious adaptive differences, implying that simple geographic isolation was the driving force for speciation (‘neutral speciation’).
- ItemOpen AccessThe evolution of the Afrotemperate-endemic genus Macowania (Asteraceae) in the Drakensberg region of South Africa(2010) Bentley, Joanne; Verboom, George Anthony; Bergh, Nicola GThe cosmopolitan Asteraceae tribe Gnaphalieae, or paper daisies or everlastings, form a significant component of both the dry and cool temperate floras of southern Africa. Within this tribe exists a small Afrotemperate genus, Macowania, endemic to the grassland biome of South Africa and occurring almost exclusively within the Drakensberg region, apart from two disjunct species in North Africa. The age, relationships and geographic origin of Macowania is investigated in order to provide insight into the factors affecting speciation, especially uplift events, on this small Afrotemperate genus. A well-supported phylogenetic hypothesis based on both nuclear and chloroplast genes suggests that Macowania is sister to a clade corresponding to the Relhania clade s.s., and that these are in turn sister to a clade containing the genera Athrixia and Pentatrichia. Macowania is monophyletic only with the inclusion of the enigmatic monotypic genus Arrowsmithia, resulting in the future synonymy of Macowania with Arrowsmithia. The anomalous species M. pinifolia, previously part of the genus Athrixia, is placed in a polytomy with the Relhania s.s. clade and the remaining species of Macowania and Arrowsmithia. DNA sequence data could not be obtained for several Macowania species, including the taxa from North Africa. The placement of these species within Macowania is confirmed by means of a parsimony analysis of morphological characters against a molecular backbone constraint tree. One species, M. tenuifolia, is well-supported in two different placements within Macowania by chloroplast and nuclear DNA sequence data. The best position of this species is inferred by incongruence decomposition analysis and morphological affinities. Bayesian relaxed clock methods and ancestral area reconstruction using maximum likelihood and squared change parsimony estimate the age and ancestral area of the genus, and determine the timing and route of colonisation of the Drakensberg. Diversification within Macowania is consistent in timing with the uplift events during the Miocene and Pliocene that resulted in significant vertical movement in eastern South Africa, suggesting that colonisation of the high-elevation Drakensberg grassland by Macowania was promoted by uplift. The topographic heterogeneity and increased river action resulting from the uplift may also have promoted evolution into new habitats and potentially mediated the movement of the ancestor of Macowania into the Drakensberg region via riparian habitats.
- ItemOpen AccessA molecular physiological review of vegetative desiccation tolerance in the resurrection plant Xerophyta viscosa (Baker)(Springer, 2015-08) Farrant, Jill M; Cooper, Keren; Hilgart, Amelia; Abdalla, Kamal O; Bentley, Joanne; Thomson, Jennifer Ann; Dace, Halford; Mundree, Sagadevan G; Rafudeen, Mohamed SXerophyta viscosa (Baker) is a monocotyledonous resurrection plant from the family Vellociacea that occurs in summer-rainfall areas of South Africa, Lesotho and Swaziland. It inhabits rocky terrain in exposed grasslands and frequently experiences periods of water deficit. Being a resurrection plant it tolerates the loss of 95 % of total cellular water, regaining full metabolic competency within 3 days of rehydration. In this paper, we review some of the molecular and physiological adaptations that occur during various stages of dehydration of X. viscosa, these being functionally grouped into early and late responses, which might be relevant to the attainment of desiccation tolerance. During early drying (to 55 % RWC) photosynthesis is shut down, there is increased presence and activity of housekeeping antioxidants and a redirection of metabolism to the increased formation of sucrose and raffinose family oligosaccharides. Other metabolic shifts suggest water replacement in vacuoles proposed to facilitate mechanical stabilization. Some regulatory processes observed include increased presence of a linker histone H1 variant, a Type 2C protein phosphatase, a calmodulin- and an ERD15-like protein. During the late stages of drying (to 10 % RWC) there was increased expression of several proteins involved in signal transduction, and retroelements speculated to be instrumental in gene silencing. There was induction of antioxidants not typically found in desiccation-sensitive systems, classical stress-associated proteins (HSP and LEAs), proteins involved in structural stabilization and those associated with changes in various metabolite pools during drying. Metabolites accumulated in this stage are proposed, inter alia, to facilitate subcellular stabilization by vitrification process which can include glass- and ionic liquid formation.
- ItemOpen AccessPhylogenetics and biogeography of the relhanioid paper-daisy lineage (Asteraceae: Gnaphalieae) : palaeoenvironmental evolution, migration and speciation in southern Africa and the greater Afrotemperate regions(2014) Bentley, Joanne; Verboom, Tony; Bergh, NicolaThe true circumscription and subtribal division of Gnaphalieae is currently not known, and a series of recent molecular phylogenetic analyses have indicated that the previously-accepted subtribal delimitation of Anderberg (1991) comprises non-monophyletic entities (Bayer et al. 2000; Bergh & Linder 2009; Ward et al. 2009). Anderberg's (1991) morphological parsimony analysis identified five subtribes, including the largely southern African subtribe Relhaniinae, considered by Linder (2003) to be the tenth-largest “Cape Floral Clade”, as well as a non-classified group of taxa which he considered putatively “basal” to Gnaphalieae. A subsequent molecular analysis (Bayer et al. 2000) indicated that many of the taxa from Anderberg's (1991) subtribe Relhaniinae and the southern African members of the “basal taxa” constitute a single lineage. This lineage, termed the “Relhania clade” by Bergh & Linder (2009), is identified by several studies as the earliest-diverging lineage in Gnaphalieae (Bayer et al. 2000; Bergh & Linder 2009; Ward et al. 2009). The Relhania clade (whose members will hereafter also be referred to as “relhanioid” taxa) forms the focus of this thesis. To date, only placeholder representatives of relhanioid species have been represented in phylogenetic analyses (Bayer et al. 2000; Bergh & Linder 2009; Klaassen & Bergh 2012; Montes-Moreno et al. 2010; Smissen et al. 2011; Ward et al. 2009); thus the Relhania clade as currently defined comprises only 24 species. On morphological grounds, the following taxa are likely to be relhanioid: Antithrixia (monotypic), Arrowsmithia (monotypic), Athrixia (14 sp.), Comborhiza (ditypic), Leysera (3 sp.), Macowania (12 sp.), Nestlera (monotypic), Oedera (18 sp.), Oreoleysera (monotypic), Pentatrichia 4 (6 sp.), Phagnalon (41 sp.; three of which are subspecific), Relhania (13 sp.), Rhynchopsidium (2 sp.) and Rosenia (4 sp.). If all these taxa are confirmed to be members of the Relhania clade, the group will comprise a total of 119 species in 14 genera. Two further genera, Alatoseta (monotypic) and Philyrophyllum (ditypic) are believed to be closely-related to, if not members of, the Relhania clade (Anderberg 1991; Montes-Moreno et al. 2010) although they are morphologically anomalous taxa whose relationships are poorly understood.
- ItemOpen AccessA preliminary study of Gelidium capense in culture(2010) Bentley, Joanne; Bolton, John JSome preliminary investigations of the effects of temperature, light intensity, salinity and to a lesser extent, water movement, were performed under controlled laboratory culture conditions on the subtidal red alga Gelidium capense, with regards to its potential for aquaculture for its use in the agar and paper-making industries. Agar was also extracted from a wild population and its concentration measured. Four temperature conditions {l0°C, 15°C, 20°c and 25°C) and three salinities (35ppt, 18ppt and 9ppt) were tested as well as four irradiances (120-140 μmol photons m⁻²s⁻¹ , 80-100 μmol photons m⁻²s⁻¹, 60-70 μmol photons m⁻²s⁻¹ and 30-50 μmol photons m⁻²s⁻¹). Water movement was achieved either through aeration or using a flask shaker. A combination of full salinity {35ppt) and 15°C temperature with a light intensity of 80- 100 μmol photons m⁻²s⁻¹ yielded the most optimal growth rates (5 .07% day⁻¹) while poor growth rates (- 1.61% day⁻¹) were observed for the 18ppt and 9ppt salinities and the lowest light intensities. Interestingly, G. capense did not thrive at 20°c or 25°C and instead discoloured rapidly, showed necrosis within a few days, which is in contrast to the findings of most studies focussed on other species of Gelidium under similar conditions. Slow growth rates were achieved at 10°c. The mean agar yield measured ten percent (9.66% ± 1.81) of dry algal weight which is less than a third of the agar yields of some other species of Gelidium and Graci/aria. This suggests that this species may not be as valuable as other Gelidium species in terms of its agar content. It does, however, have high rhizine content and this may lend it to be beneficial in the papermaking industry.