Gethyllis multifolia L. Bolus and G. villosa Thunb. are winter-growing, summerblooming,
deciduous and bulbous geophytes that grow naturally in the semi-arid
succulent Karoo biome of South Africa. Both species grow under full sun
conditions and have four distinctive growth phases: a winter (cold and wet)
growing phase, leaf senescence phase towards spring, flowering phase during the
hot and dry summer months, and fruit and leaf formation phase in autumn. The
medicinal uses of this genus (including G. multifolia “Kukumakranka” and G.
villosa “hairy kukumakranka”) range from cures for colic, digestive disturbances,
teething problems, fatigue, boils, bruises and insect bites, to being used as an
aphrodisiac. Gethyllis multifolia is threatened in its natural habitat and is listed in
the ‘Vulnerable’ category of the ‘Red Data List of Southern African Plants’ and
the ‘IUCN-World Conservation Union List of Plants’. The literature indicate that
the habitats of both species are being exposed to drier conditions and is further threatened by the encroachment of invasive indigenous plant species. It is not
known to which extent these factors may pose a threat to the existence of both
species. The first objective of this investigation was to determine the costs of vegetative
and reproductive growth during the seasonal life cycle of the plant, using carbon
(C) and nitrogen (N) as a physiological currency. The second objective was to
elucidate a functional basis to explain the difference in the conservation status of
both species in their natural habitat. Both species were subjected to drought and
shading as environmental stresses and the plant physiological performance was
investigated via photosynthetic gas exchange. The third objective of the study
was to evaluate the antioxidant content (total polyphenol, flavonol/flavone and
flavanone content) and antioxidant capacity [ferric reducing antioxidant power
(FRAP), oxygen radical absorbance capacity (ORAC) and 2,2'-azino-di-3-
ethylbenzthiazoline sulphonate (ABTS) radical cation scavenging ability] of
natural populations and plant samples that were exposed to photo- and -drought
environmental stresses. This study was done to elucidate the antioxidant profile
of plant parts of natural populations as well as providing farmers, traditional
healers and pharmaceutical companies with cultivation environmental conditions
to enhance the antioxidant properties of the species. This investigation also
attempted to isolate and characterize, by means of thin-layer chromatography
(TLC) and column chromatography (CC), natural compounds from both species
to lend support to the purported antioxidant benefit of both species and to further
lend support to claims made by traditional healers of the medicinal potential of the genus. This study, however, did not engage in any in vivo studies or human trials
to support published literature of the medicinal benefits of the genus. The photosynthetic adaptation studies indicated that G. villosa had a better
photosynthetic performance than G. multifolia during both drought and low light
conditions because of the inability of G. multifolia to adapt to a wider range of
environmental extremes. The C and N cost of growth and reproduction studies
revealed that G. villosa had a more efficient resource utilisation strategy for both
growth and reproduction. These physiological responses suggest that G. villosa,
in general, has a more efficient survival strategy and that G. multifolia will
struggle to adapt to drier environmental conditions, as well as growing in the
shade of encroaching invasive plant species. To conclude, this could be a
contributing factor as to why G. multifolia is threatened in its natural habitat and
G. villosa not. The antioxidant content-and -capacity study on natural populations of both species
revealed the highest total polyphenol content, FRAP and ORAC values for the
flowers and fruits of G. multifolia and G. villosa compared to other plant parts.
These values were found to be in line with and in some cases higher than most
commercial fruits and vegetables. The antioxidant activity during drought and
photo-stress of the leaves, bulbs and roots was found to be highest in the roots of
both species during drought stress. Gethyllis multifolia, in general, exhibited
higher total polyphenol content than G. villosa, with the highest content measured
during drought stress in the roots of G. multifolia. Phytochemical investigation of the leaves, bulbs and roots of G. multifolia and G. villosa revealed the presence of
tannins, flavonoids, phenolics, saponins, glycosides as well as essential oils, while
alkaloids were absent. The chromatographic profiles of the leaves, bulbs and
roots of both species further indicated that the roots of G. multifolia contained the
highest concentration of natural products, compared to G. villosa and other plant
parts. Further in-depth studies on the roots of G. multifolia led to the isolation and
characterization of three known flavonoids, of which one was also isolated as its
endogenously acetylated derivative. In contrast to the fact that both species had a
high polyphenol content and exhibited high antioxidant activity, the isolated
compounds in this study revealed very low antioxidant activity. However, the
literature revealed that some of these isolated compounds exhibit antifungal,
antibacterial, antiangiogenic and anticarcinogenic properties in vitro, which could
be ascribed to the medicinal applications of plant parts of certain species
belonging to this genus. Furthermore, this study suggests that further chemistry
and pharmaceutical research on the genus, Gethyllis, in specific the flowers and
fruit of these two species, be pursued. / Philosophiae Doctor - PhD
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uwc/oai:etd.uwc.ac.za:11394/3372 |
| Date | January 2012 |
| Contributors | Mabusela, Wilfred T., Valentine, Alexander J., Marnewick, Jeanine L. |
| Publisher | University of Western Cape |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Rights | University of Western Cape |
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