Browsing by Author "Nicholas, Ashley."

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Biosystematic studies in Southern African species of Strychnos L. (Loganiaceae)
(2014) Adebowale, Adekunle.; Nicholas, Ashley.; Lamb, Jennifer Margaret.; Naidoo, Yougasphree.
Strychnos L. is the largest genus of the pantropical or subtropical family Loganiaceae with about 200 species. Their habits range from trees and shrubs in open areas to lianas in rain forests. The genus is well-known as a source of alkaloids such as strychnine and brucine and other allied compounds, all of which have been used medicinally and in curare formulation for centuries. While taxonomic circumscription of the genus has never been contentious, there is no consensus about infrageneric affiliations, the latest of which recognises 12 sections based on morphological characters. Recent molecular evaluation of the genus on a global scale with the internal transcribed spacer (ITS) marker suggests that many of the currently recognised sections are not monophyletic. An understanding of regional patterns of evolution, which is relevant for biodiversity conservation, requires an in-depth study of the focus group on a regional scale. Using a multiplicity of approaches from morphological and molecular to biogeographical, this study is an attempt at elucidating diversity patterns at different levels among the southern African species of Strychnos. Various combinations of morphological attributes from branches, leaves, flowers and fruits distinguish seemingly homologous clusters of species, sometimes supported by molecular data. A lack of molecular support for a hypothetical relationship may viii indicate case(s) of convergent evolution in these features across the taxa involved. Molecular phylogenies based on the ITS and chloroplast markers confirm the nonmonophyletic nature of all but section Spinosae. Proposals for sectional recircumscriptions of the genus are provided. Patterns of speciation within Strychnos suggest a Miocene origin in the rain forests along the South America/Guinea-Congolian axis. Within the southern African subcontinent, the evolution of the genus carries a strong ecological signature along either the forest or savanna biome, with many accompanying morphological adaptations for the respective habitats. The non-synonymy of S. gerrardii with S. madagascariensis is demonstrated with multiple sources of data, as a case of integrative taxonomy succeeding where single-source data approaches might have failed. Routes to current distribution of the genus in southern Africa are hypothesised to involve a combination of palaeo-climatic oscillations and allopatric speciation, consistent with the process indicated in many other plant groups for the region. The findings are discussed in the wider context of their implications for taxonomy and biodiversity conservation in the face of climate change, food security and other relevant issues in systematics.
In vitro studies and phytocompound analysis in Lessertia frutescens (Fabaceae)
(2011) Shaik, Shakira.; Nicholas, Ashley.; Singh, Nisha.
The cancer bush (Lessertia frutescens L.) is an important leguminous perennial native to southern Africa and has been used for centuries in traditional medicine by the continent’s diverse cultural groups. Like many other legumes, the seeds of this species exhibit dormancy. Moreover, woody plants are typically difficult to propagate in in vitro culture systems. But in vitro shoot cultures are valuable in providing an alternative means of deriving desired secondary metabolites or phytocompounds, under controlled conditions. This study describes novel protocols for breaking seed dormancy, rapid and efficient in vitro propagation, bioreactor culture, and comprehensive phytochemical data following screening and analysis of in vitro and field extracts of L. frutescens. Experiments using physical, mechanical and chemical pre-sowing treatments were conducted to determine the germination response of this species. The results indicated that seeds of L. frutescens exhibited exogenous dormancy due to the inhibitory effect of the hard coat on germination. Seed dormancy was released by mechanical scarification in which 100 % germination was achieved. In vitro propagation studies using single node explants in Murashige and Skoog (MS) medium supplemented with combinations of different concentrations of benzyladenine and naphthaleneacetic acid revealed a maximum number of 10 shoots per explant in solid medium, and 12.9 shoots per explant in liquid medium inside a temporary immersion bioreactor. Indirect shoot organogenesis and plant regeneration using rachis and stem segments was achieved with the highest percentage of explants forming shoots (88.8 %) from rachis explants cultured onto MS medium supplemented with thidiazuron. Direct shoot organogenesis from hypocotyl and cotyledon segments was also achieved in L. frutescens. The highest shoot regeneration using hypocotyls (83 %) was obtained in MS medium supplemented with kinetin whilst the highest shoot regeneration using cotyledons (46 %) was obtained in MS medium supplemented with kinetin in combination with benzyladenine. Successful rooting (up to 80 %) and acclimatization (up to 90 % survival rate) was attained. Spectrophotometric and gravimetric methods indicated that saponins were the most abundant, followed by phenolics, flavonoids and then alkaloids in in vitro leaf extracts then in field leaf extracts and seed extracts, respectively. After qualitative analysis these extracts were also found to contain tannins, phlobatannins and cardiac glycosides of medicinal interest. By using gas and liquid chromatography the presence of the medicinally important L-canavanine, gamma amino-butyric acid and D-pinitol was verified in in vitro leaf, field leaf and seed extracts. In vitro leaves had higher quantities of all compounds, except for D-pinitol. Phytocompound analysis of shoots derived from several of the cytokinin-enhanced media showed that these organs contained higher quantities of L-canavanine compared to the control. This study, therefore, highlights the potential techno-economic production of medicinal phytocompounds from in vitro leaves of L. frutescens following large scale production using the protocols described in this study.
The leaf secretory apparatus of Hibiscus surattensis and Hibiscus sabdariffa (Malvaceae) : micromorphology, histo-phytochemistry and ultrastructure.
(2015) Raghu, Kashmira.; Naidoo, Yougasphree.; Nicholas, Ashley.
The research presented here forms the basis of the ethnobotanical and ethnopharmacological evaluation of Hibiscus surattensis, which is a widely distributed vegetable and medicinal shrub used by African and Indian traditional practitioners. Using light microscopy together with advanced electron microscopy techniques, the leaf topography and internal structure was examined. A closely related species, Hibiscus sabdariffa was also investigated for foliar and histophytochemical comparisons. Hibiscus sabdariffa is a widely consumed medicinal species with well-known biological activity and known chemical principles. Both species belong to the section Fucaria within the genus Hibiscus. Analyses of foliar secretory tissues showed that both H. surattensis and H. sabdariffa were characterised by capitate trichomes as well as mucilage-producing ducts and idioblasts. Head cells of capitate trichomes were between 5 and 7, while lignified stalk cells occurred in numbers of 2 or 3. A basal cell supporting the trichome was implanted in the epidermis comparative study between the two species showed some variation of chemical composition in trichome head cells. Polysaccharidic, alkaloids, phenolic and acidic lipid components were identified for both H. surattensis and H. sabdariffa whereas H. sabdariffa showed an intense staining of proteinaceous substances. Densities of capitate trichomes varied from emergent to mature developmental stages, with the highest number occurring on the emergent abaxial surface for both H. surattensis and H. sabdariffa. However, a distinct trend was observed for H. surattensis, where a decrease in capitate trichomes with progressive development was associated with the proliferation of mucilage idioblasts, particularly on the mature adaxial surface. Mucilage producing tissues are assumed to be associated with a protective role against dehydration in a number of plant families. Idioblasts observed in H. surattensis were visible leaf surface structures, embedded in the epidermal tissues. They contained considerable amounts of acidic polysaccharides and acidic lipids, and appeared to be implicated in reducing evaporative water loss in fully expanded leaves. Mucilage ducts were identified in vascular tissue within leaf veins. They occurred parallel with the conducting tissue and comprised of an epithelial layer of cells which seemed to be secreting a mucilage into an extracellular lumen. Crystal idioblasts were also identified in tissues of both H. surattensis and H. sabdariffa. The sequestration of calcium oxalate is assumed to be governed and regulated by specialised mesophyllous idioblasts that in turn appeared to be triggered by excess calcium within the plant body to differentiate into crystal forming cells. The supposed function of calcium oxalate crystals includes mechanical support and herbivory avoidance. TEM revealed the cellular processes which involved crystal idioblast development in H. surattensis. This appeared to demonstrate that degeneration of organelles which are assumed to occur when crystals reach maximal proportions. The non-glandular trichome component of each Hibiscus species was diverse in trichome type and might have accounted for differences in leaf texture and the leaf indumentum. The prickly texture of Hibiscus surattensis was attributed to rigid stellate and falcate trichomes as well as restrorse prickles, whereas the leaves of H. sabdariffa were glabrous with few falcate, bi- and trifurcate trichomes found mainly at the base or along the midvein. Preliminary phytochemical experiments which involved methanolic, chloroform and hexane extracts, yielded favourable results, which showed that leaves of H. surattensis and H. sabdariffa were chemically similar, in this regard, the author recommended further investigation into the phytochemical nature of H. surattensis.
The micromorphological and essential oil status of the foliar secretory structures of Ocimum obovatum E. Mey. ex Benth. subsp. obovatum (Lamiaceae)
(2011) Kasim, Nazeera.; Naidoo, Yougasphree.; Nicholas, Ashley.
Ocimum obovatum E. Mey ex Benth. var. obovatum is a traditionally used medicinal plant that grows along the KwaZulu-Natal coast and the western Cape of South Africa. The plant is noted for its hair restoration properties, remedy for infantile abdominal pain and cramps and its use as an enema to treat epigastric conditions in children. The aims of this study were to document the micromorphology and ultrastructure of the foliar secretory structures responsible for the production and secretion of the essential oils and chemical composition of the secretion, which gives the plant a distinct aroma. It is believed that these oils contain the active ingredients that contribute to the medicinal properties of the plant. A variety of microscopic methods and histochemical and phytochemical tests were used to achieve this. Leaves in all stages of development were pubescent and gland dots, characteristic of plants in the genus, were found on both adaxial and abaxial surfaces. Three types of trichomes were found on both leaf surfaces across all stages of development; non-glandular trichomes and two types of glandular trichomes. Non-glandular trichomes are single, multicellular and uniseriate with microornamentation and a supportive cellular pedestal. The glandular trichomes consisted of peltate and capitate trichomes. Peltate trichomes are made up of four head cells and a very small basal cell that gives the glands the appearance of being sessile. The capitate trichomes were further divided into two types based on the morphology of the glands. Type I capitate trichomes are smaller than the larger peltate trichomes and are composed of one basal cell and a head consisting of two broad head cells. Type II capitate trichomes consisted of one basal cell, one stalk cell and a single oval head cell. Histochemical tests showed that peltate and Type I capitate trichomes have cutinized or suberized walls in the stalk cell to prevent the apoplastic flow of secretory material into neighbouring mesophyll tissue. The histochemical stains also showed that the secretory material present in the glandular trichomes are lipid in nature and essential oils are present. Ultrastructural studies showed polymorphic leucoplasts, few Golgi bodies, numerous vesicles and mini vacuoles, mitochondria and short profiles of endoplasmic reticulum cisternae. Phytochemical tests revealed the presence of essential oils that are terpene-rich. Flavonoids, tannins, saponins, terpenoids, fixed oils and fat, phenolics and cardiac glycosides were also detected in a crude ethanolic extract of the leaves. These chemical compounds appear to be responsible for the medicinal properties for which the plant is traditionally exploited.
A systematic study of the genus rhoicissus planch, (vitaceae) in KwaZulu-Natal.
(2015) Kunene, Sinethemba Faith.; Nicholas, Ashley.; Naidoo, Yougasphree.; Boon, Richard Graham Campbell.
The family Vitaceae, sometimes referred to as the grape family, comprises about 700 to 800 species and 13 to 14 genera, which includes Rhoicissus Planch. Rhoicissus contains 12 species all of which are described as climbing shrubs with tendrils that are without adhesive discs. This study was aimed at updating the taxonomy of the genus Rhoicissus in KwaZulu-Natal such that the names and number of species contained within the genus reflect the current findings. This dissertation looks primarily at the taxonomy of the leaves of the Rhocissus species of KwaZulu-Natal. The reason for this is that this work is meant to help conservationists, environmental managers, rangers, amateur botanists and others who will usually only encounters these species in their vegetative state. It is at this audience that this dissertation is aimed. Rhoicissus tridentata was found to be a complex that is made up of three subspecies: R. tridentata subsp. cuneifolia; R. tridentata subsp. diplonervia and R. tridentata subsp. tridentata. Phenetic results, scatter plots and polygonal graphs did not all support the division of R. digitata into three subspecies. Morphological results, however, did show the slight differences between the subspecies of R. digitata which are R. digitata subsp. digitata; R. digitata subsp. oravivens and R. digitata subsp. emarginata. The other species of Rhoicissus (R. revoilii; R. rhomboidea; R. sessilifolia and R. tomentosa) were all found to be distinct species.
A taxonomic reassessment of the subtribe Asciepiadinae (Asclepiadaceae) in Southern Africa : Vol. 2.
(1999) Nicholas, Ashley.; Baijnath, Himansu.; Rogers, C. B.
This study extends an earlier M.Sc. research project on the narrow-leaved species of the genus Asclepias L. (30 species) to cover the entire subtribe Asclepiadinae sensu K. Schum. in southern Africa- (182 species in 23 genera). Two genera (Eustegia R. Br. and Pentarrhinum E. Mey.) are revised and then removed from this tribe. The remaining 177 species and 21 genera form the focus of this thesis, whose principal objectives are to reevaluate the taxonomic and evolutionary significance of various macro, micro and chemical characters and then use them to produce a classification that, more closely, reflects the overall similarity and phylogeny of the taxa involved. Species and genera are recircumscribed based on the wealth of data that has come to light since the subtribe was last revised by N.E. Brown (1907-1908) some 90 years ago. This process was supplemented by extensive field work, observations on pollination and reproductive biology, ecology, biogeography, conservation and ethnobotany. The majority of this thesis consists of a compilation of 17 papers, 12 of these published and most, but not all, of the remainder in preparation for press. Two of these papers form the bulk of the taxonomy. The first deals with what was the genus Asclepias in southern Africa. The genus is now believed to be confined to the Americas. The • Botswana, Lesotho, Namibia, South Africa and Swaziland. southern African species have diverse origins and are partitioned into 7 genera, one of them (Gomphocarpus R. Br.) resurrected, two of them (Aidomene Stopp and Aspidonepsis Nicholas & Goyder) expanded and four of them (Paulforstera, Sigridia, Bruynsia and Pachyacris) described as new. Gomphocarpus is divided into two subgenera and Aidomene into four subgenera. Three new species are also described. The second paper investigates the bulk of most of the remaining genera. Kanahia R. Br., Cordylogyne E. Mey. and Fanninia Harv. remain as is. Xysmalobium R. Br., previously a genus of 19 species in southern Africa, is reduced to three species in two subgenera. Trichocodon is segregated off from Pachycarpus E. Mey. as a new genus. While two species, previously placed in Xysmalobium, are added to Pachycarpus, but placed in the new subgenus Parapodiopsis. Parapodium E. Mey. is reduced from three to two species and Periglossum Decne. is reduced from five to three species, one of them newly described. Woodia Schltr. and Stenostelma Schltr. are both considerably expanded, mainly with species previously housed in Xysmalobium), and the former divided into two subgenera. The third paper briefly looks at the Schizoglossum E. Mey., Miraglossum Kupicha and Aspidoglossum E. Mey. Some changes are suggested but, as further work is needed, none are formalised. As a corollary to the taxonomy, secondary metabolite profiles of 38 species and 17 genera were done using Thin layer Chromatography. The results sometimes confirmed morphological patterns and sometimes were at odds with them. A trend from simple profiles to more complex profiles seems to echo the suspected phylogeny of the genera within this sub tribe. Some species and genera have greater chemical diversity than others and secondary metabolites are shown to vary considerably in different parts of a single plant. As a supplement to the above work or because they are cited elsewhere in the dissertation, published papers dealing with floral structure, the asclepiadaceous work of Rudolf Schlechter, as well as miscellaneous works in the tribe Stapelieae, are also given.