Student Number : 0009899J -
PhD thesis -
School of Therapeutic Sciences -
Faculty of Health Sciences / The genus Eriocephalus commonly known as ‘wild rosemary’, ‘Cape snow bush’, or
‘kapokbos’ is a member of the family Asteraceae (tribe Anthemideae). The genus is endemic
to southern Africa, with the highest concentration of species in the Western and Northern
Cape. The genus comprises 32 species and a total of 42 taxa, which are distributed in South
Africa, Namibia, Botswana, and Lesotho. The characters used in species delimitation are
purely based on morphological variation in floral and foliar parts and are highly homoplastic
due to phenotypic plasticity. In many cases these features are not sufficiently distinctive, as
some taxa tend to exhibit dimorphism in some character states such as the presence of
opposite and alternate leaves. In some species there is extensive intergrading of the major
diagnostic characters leading to uncertainty in species delimitation. Both chemical and
molecular characters were used in this study in an attempt to evaluate current species
delimitations in the genus, along with species-level relationships and affinities. The genus is
also economically important with some of its members used as medicinals, fodder, perfumes,
and cosmetics. This warrants investigation into the phytochemistry and biological activity of
these species in order to determine a scientific rationale for their traditional uses. For this
reason, the antimicrobial, antiinflammatory, antioxidant activities, and inhibition of
acetylcholinesterase by the volatile oils and leaf extracts of the genus, which are relatively
unknown for most members of the genus, were also investigated.
Representatives of 22 species of the genus, eight of which were from Namibia and 14 from
South Africa were collected from wild populations. In most cases multiple collections per
population per species were considered. Aerial plant parts were hydrodistilled to obtain the
essential oils, and phenolics were extracted from leaves using acetone. Essential oils were
analysed by thin layer chromatography (TLC), gas chromatography (GC), gas
chromatography coupled to mass spectroscopy (GC/MS), and phenolics were analysed using
thin layer chromatography (TLC) and high performance liquid chromatography (HPLC/UV).
Biological assays were carried out using the 5-lipoxygenase enzyme to evaluate
antiinflammatory activity; disc diffusion and microtitre plate dilution assays were used to
assess antimicrobial activities of selected fungi and bacteria; the TLC-DPPH and DPPHmicrotitre
methods were used to investigate antioxidant activities and a TLC-bioautographic
assay was used for testing the inhibition of the acetylcholinesterase enzyme. Total genomic
DNA was extracted from silica dried leaf material. The non-coding plastid DNA regions, the psbA-trnH intergenic spacers and the internal transcribed spacer (ITS) region of nuclear
ribosomal DNA were amplified, and sequenced and analysed using the parsimony algorithm.
The essential oils are largely comprised of acyclic, monocyclic, and bicyclic regular and
irregular mono- and sesquiterpenes of various structural groups. Two hundred compounds
were noted in the essential oils with some of the common constituents being; α- and β-pinene,
yomogi alcohol, ρ-cymene, 1,8-cineole, camphor, 4-terpineol, spathulenol, caryophyllene
oxide, α-copaene and β-caryophyllene. Most of the species have a relatively high content of
1,8-cineole and camphor. Twenty-two chemotypes were noted and the potential for
commercial development in the flavour, fragrance and pharmaceutical industries has been
recorded. Among the favourable chemotypes noted includes the camphor, 1,8-cineole,
bisabolol oxide B and nerolidol rich oils. However, due to the extensive variability in the
essential oil profiles, standardization of oils in commercial development is crucial.
The leaf extracts comprised of flavonoids with the flavones and flavanones as the major
structural types present in most species. The terpene and flavonoid chemistry of the genus is
highly divergent even among multiple individuals of the same species and hence not a good
taxonomic marker for specific delimitation as no coherent groups was evident although some
phytochemical congruence has been noted between some of the taxa.
The DNA sequence data revealed lack of variability in the non-coding regions psbA-trnH and
trnL-F among species of the genus. The nuclear DNA region (ITS) was variable but the
number of characters separating taxa was too few for resolution of relationships between taxa.
Presence of highly divergent paralogous repeats of ITS were also noted in some taxa. The
combination of molecular and chemical data did not resolve the species delimitation problems
due to the highly variable distribution of characters within a single species. The patterns of
variation observed in the genus may be attributed to chemical convergence, divergence,
hybridisation, differential gene expression, polymorphism and allelochemical diversification
among other factors. The lack of coherence in the phylogenetic and phenetic groupings of the
various taxa implies that the current species boundaries may not be a true reflection of natural
taxonomic entities. The use of multiple taxa in taxonomic studies is strongly recommended
due to the extensive variability noted in the chemical profiles of the taxa that is also depicted
in the phylogenetic histories. It also implies that caution should be taken in bioprospecting for
new natural products for commercial development, as plant chemical profiles especially from the same species can be very variable. This implies carrying out exhaustive population and
genetic studies for evaluation of diversity in the study group.
In the antimicrobial assay, the oils were more active against the Gram-positive bacteria (2-16
mg/ml) and yeasts (1-16 mg/ml). Bacillus cereus and Cryptococcus neofomans were the most
susceptible pathogens to the oils. The extracts exhibited low activity against the test
pathogens except E. aromaticus and E. pinnatus with activity of 0.2 mg/ml against
Staphylococcus aureus and Bacillus cereus respectively. The susceptibility of the fungal
pathogens Cryptococcus neoformans and Candida albicans and the Gram-positive bacteria
Bacillus cereus to the oils and extracts is an indication of the potential for use of the members
of the genus as natural antibiotics. The essential oils exhibited antiinflammatory activities
with IC50 values ranging between 19.0-98.6 μg/ml. The oils did not show antioxidant activity
at the starting concentration of 100 μg/ml but the acetone leaf extracts exhibited antioxidant
activities with IC50 values ranging between 21.5-79.6 μg/ml. The essential oils showed
inhibitory activity against acetylcholinesterase enzyme. The biological activity of the oils
indicates that most of the traditional uses are influenced by the presence of the oils. The in
vitro biological activity of the essential oils and extracts against the test pathogens provides a
scientific basis for the use of some of the members in traditional herbal remedies and validates
the use of some of the members of the genus for treatment of respiratory tract infections,
gastro-intestinal disorders, mental conditions, dermal infections, and inflammation. The study
records the biological activities for some of the species for the first time and their potential for
use in flavourings, perfumery, cosmetics, as sources of antimicrobial drugs, permeability
enhancers in pharmaceutical formulations and for use as industrial oils.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/1582 |
| Date | 01 November 2006 |
| Creators | Njenga, Elizabeth Wanjiku |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 5650619 bytes, 88800 bytes, application/pdf, application/pdf, application/pdf, application/pdf |
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