Ben-Erik Van Wyk

Osmitopsis asteriscoides(Asteraceae)-the antimicrobial activity and essential oil composition of a Cape-Dutch remedy

The essential oil composition and antimicrobial activity of Osmitopsis asteriscoides, a medicinal plant used in traditional herbal preparations in South Africa has been investigated. Three different antimicrobial methods (disc diffusion, minimum inhibitory concentration by micro-titer plate and time-kill studies) were comparatively evaluated against Candida albicans, Staphylococcus aureus and Pseudomonas aeruginosa. A preliminary screening was done using the disc diffusion method on nine bacterial and four fungal isolates. Minimum inhibitory concentrations showed some correlation with the disc diffusion method. However, time-kill studies appear to be a more superior method for determining antimicrobial activity of volatile compounds such as essential oils. Two moderately susceptible and one resistant organism were selected to further demonstrate the variability between the three methods. The antimicrobial activity of the essential oil, tested by means of time-kill methodology at concentrations ranging from 0.5 to 2% (v/v) indicate a strong fungicidal activity against Candida albicans and the oil was also found to be bacteriostatic against Staphylococcus aureus in a concentration-dependent manner. The essential oil rapidly reduced viable counts of Pseudomonas aeruginosa, but regrowth was noted after 240 min. The results have been generated in duplicate in separate microbiology laboratories using different time-kill methods and the results are congruent. The two major essential oil components camphor and 1,8-cineole were investigated indicating the positive antimicrobial efficacy of 1,8-cineole independently and in combination with camphor. In addition to (-)-camphor and 1,8-cineole, 40 compounds were identified by GC-MS in the hydro-distilled essential oil. The high concentration of cineole and camphor and their synergistic effect is presented as a possible explanation for the traditional use of Osmitopsis asteriscoides for treating microbe-related illnesses.

Phylogenetic relationships in Asphodelaceae (subfamily Alooideae) inferred from chloroplast DNA sequences (rbcL, matK) and from genomic fingerprinting (ISSR)

Two independent lines of molecular evidence have been studied to explore phylogenetic relationships in the family Asphodelaceae. Genomic fingerprinting by ISSR (Inter Simple Sequence Repeats) analysis was compared to sequence data of the chloroplast genes matK and rbcL. Molecular data indicate that some long-established taxonomic concepts would have to be re-evaluated. The subfamily Asphodeloideae clusters as a sister group to a distinctly monophyletic Alooideae. However, several Alooideae genera, including Aloe and Haworthia, are apparently not monophyletic. From a molecular point of view, Haworthia can be divided into two distinct groups that agree closely with the current subgeneric classifications a monophyletic group including species of subgenus Haworthia, and a second polyphyletic group with the subgenera Hexangulares and Robustipedunculares. This second Glade includes Poellnitzia, Astroloba, Gasteria and even one Haworthia-like aloe (Aloe aristata). In the polyphyletic assemblage currently classified as Aloe, several smaller clades can be recognised, often reflecting morphological, chemical and geographical discontinuities. The tree aloes (sections Aloidendron and Dracoaloe) and climbing aloes (series Macrifoliae) appear to have separated early in Alooideae, while other groups (e.g., the flavonoid-containing group and a Ma agascan group) are embedded within and amongst other genera. Chortolirion clusters with the grass-like aloes (section Graminialoe Reynolds, syn. Leptaloe Berger), A. boylei and A. verecunda, on a well-defined branch. The current taxonomic system clearly does not reflect the phylogenetic affinities and relationships amongst the succulent genera Aloe, Astroloba, Chortolirion, Gasteria, Haworthia, and Poellnitzia.

Nectar sugar composition in the subfamily Alloideaec (Aphodelaceae)

Abstract HPLC analyses of nectar samples from 82 species of the genera Aloe, Astroloba, Chortolirion, Gasteria, Haworthia, Kniphofia, Lomatophyllum and Poelnitzia have shown that the sugar compoisition of nectar is remarkably invariable within each of the genera. In the Alloideae, distinct suprageneric groups can be distinguished, based only on the relative proportions of sucrose, glucose and fructose. Three nectar types are present in the subfamily: (1) an alooid type (in Aloe, Kniphofia, Lomatophyllum and Poellinitzia) with less than 5% sucrose and equal proportions of glucose and fructose; (2) a gasterioid type (in Gasteria only) with sucrose dominant and equal proportions of glucose and fructose; (3) a haworthioid type (in Astroloba, Chortolirion and Haworthia) with sucrose dominant but with much more glucose than fructose.

Apparent Absorption Efficiencies of Nectar Sugars in the Cape Sugarbird, with a Comparison of Methods

Nectarivore sugar preferences and nectar composition in the Cape Floristic Kingdom (southern Africa) differ from trends reported for analogous systems in America and Europe in that sugarbirds and sunbirds show no aversion to sucrose, which is the dominant nectar sugar in many of their food plants. To elucidate the physiological bases (if any) of nectarivore sugar preferences, we determined apparent sugar absorption efficiencies in a passerine endemic to this region, the Cape sugar‐bird Promerops cafer. Apparent absorption efficiencies for the three major nectar sugars, sucrose, glucose, and fructose, were extremely high (>99%), as in other specialized avian nectari‐vores. Xylose, a pentose sugar recently reported in the nectar of some Proteaceae, was absorbed and/or metabolized inefficiently, with a mean of 47.1% of ingested sugar recovered in cloacal fluid. We did not measure the proportions of xylose that were absorbed and/or metabolized. We also compared three methods of estimating absorption efficiency: (1) measurements of total sugar in cloacal fluid with refractometry, without correction for differences between volumes of ingesta and excreta; (2) the same measurements combined with correction for volume differences; and (3) HPLC analyses quantifying individual sugars in cloacal fluid, with correction for volume differences. Refractometry has been frequently used in previous studies. For all sugars except xylose, method 1 yielded results similar to those obtained with method 2, but the convergence was artifactual, and we do not recommend use of this method. Apparent absorption efficiencies calculated with method 2 underestimated true absorption efficiency, because refractometry measures nonsugar solutes, but this error is biologically significant only when efficiencies are low.

Nectar sugar composition in Erica

Abstract The nectar sugar compositions of 50 species of Erica have been analysed by HPLC. A marked dichotomy in nectar sugars was evident within the genus. Of the ornithophilous species analysed, 29 had sucrose-dominant nectars and eight had hexose-dominant nectars. Both nectar types occurred within the artificial sections into which the genus is currently divided. Our results contradict the idea that flowers pollinated by passerine birds produce hexose-dominant nectars.

The major phenolic compounds in the leaves of Cyclopia species (honeybush tea)

Abstract The phenolic compounds of the leaves of Cyclopia species (tribe Podalyrieae) are of both chemotaxonomic and commercial interest, as the leaves are used to brew a herbal drink known as honeybush tea. Despite the commercial importance of Cyclopia, virtually nothing was known about the chemistry of the leaves prior to the present work. Methanolic extracts from leaves of 22 species were screened for the presence and distribution of phenolic compounds. Three major constituents of the leaves were identified as mangiferin (a xanthone) and glycosides of the flavanones hesperitin and isosakuranetin. The combination of these three compounds is a unique character for Cyclopia, as none of them are present in any of the other genera of the tribes Podalyrieae and Liparieae. Various combinations of the three compounds occur in the different infrageneric groups, but the species are remarkably similar. These results are thus of chemotaxonomic significance at the generic rather than infrageneric level.

Phylogenetic Relationships of Tribe Crotalarieae (Fabaceae) Inferred from DNA Sequences and Morphology

Abstract Tribe Crotalarieae is a large and diverse group of papilionoid legumes that largely occur in Africa. A systematic study of generic relationships within the tribe was undertaken using nucleotide sequences from the internal transcribed spacer (ITS) of nuclear ribosomal DNA, the plastid gene rbcL, and morphological data. The Crotalarieae are supported strongly as monophyletic and sister to the tribe Genisteae. Lebeckia, Lotononis, and Wiborgia are all paraphyletic in the molecular analyses and morphological data support the division of Lebeckia into three more natural genera (one of which includes the monotypic North African Spartidium). Four major lineages were identified within the tribe based on sequence data: the “Cape” group, comprising Aspalathus, Lebeckia, Rafnia, Spartidium, and Wiborgia; the Lotononis group, comprising Lotononis pro parte, Pearsonia, Robynsiophyton, and Rothia; a group comprising Lotononis section Leptis, L. section Listia, and allies; and the Crotalaria group, comprising Bolusia, Crotalaria, and Lotononis hirsuta (Lotononis section Euchlora). Morphological analysis yields a similar topology, except that Lotononis is monophyletic if L. hirsuta were excluded. When the molecular and morphological data sets are combined, the same major clades are retrieved as in the molecular analysis, with the notable exception that Lotononis and Lebeckia senso stricto are supported as monophyletic. The results from this study have important implications for the classification of the tribe Crotalarieae and present an important step towards a natural and phylogenetic generic classification for the tribe.

Nectar sugar composition in Southern African Papilionoideae (Fabaceae)

Abstract The nectar sugar composition of several genera of the subfamily Papilionoideae (Fabaceae) have been analysed, including many southern African endemic genera of the tribes Crotalarieae, Podalyrieae and Liparieae. Nectar sugars were found to be conservative characters with limited taxonomic value. Most of the samples contained high concentrations of sucrose, reaching nearly 100% in species of Virgilia and Cyclopia of the tribe Podalyrieae. Fructose and glucose are present in more or less equal amounts, and are the dominant sugars in the nectar of Erythrina and Sutherlandia (both bird-pollinated) but also in Pearsonia and some species of Lotononis both bee-pollinated). The conservative nature of nectar sugars is clearly seen in the two species of Liparia (tribe Liparia) where there are morphological adaptations to bird pollination in L. splendens but no corresponding difference in the sugar composition of the nectar.

Chemotaxonomic significance of anthraquinones in the roots of asphodeloideae (asphodelaceae)

Abstract The distribution of seven anthraquinones in the roots of some 46 species belonging to the genera Asphodelus, Asphodeline, Bulbine, Bulbinella and Kniphofia was studied by TLC and HPLC, 1,8-Dihydroxyanthraquinones based on a chrysophanol unit are the main constituents of the subterranean metabolism in the subfamily Asphodeloideae. The genera Bulbine, Bulbinella and Kniphofia elaborate knipholone-type compounds. These compounds appear to be characteristic constituents for the three genera Bulbine, Bulbinella and Kniphofia and support the idea that Kniphofia is not related to the Alooideae.

A review of the use of allozyme electrophoresis in plant systematics.

Abstract The role of electrophoretic data is discussed as it applies to plant taxonomy and systematic studies. Neis (Am. Nat. 106 (1972) 283–292; Genetics 89 (1978) 583–590) genetic distances calculated for a large number of populations, species and genera were taken from published data. The relation between Neis genetic identity measures and taxonomic rank (populations, species and genera) are shown graphically. The graphs obtained in this way (from 3021 pairs of plant taxa) differ substantially from previous graphs published by Thorpe (Ann. Rev. Ecol. Syst. 13 (1982) 139–168; in: G.S. Oxford, D. Rollinson (Eds.), Protein Polymorphism: Adaptive and Taxonomic Significance, Academic Press, London, 1983, pp. 131–152) and Thorpe and Sole-Cava (Zool. Scripta 23 (1994) 3–18). These authors suggested that the divergence between the different taxonomic ranks is roughly similar across a wide range of taxa. The latter was based on values for 2664 (Thorpe, 1982) and 8060 (Thorpe, 1983) pairs of animal and plant taxa, but the plant data contributed little to the total. For any given taxonomic rank, we found that plants are genetically more closely related than animals (possibly with the exception of birds). This result is important because the empirical relationships of genetic distance measures, to different levels of taxonomic separation, is often used for distinguishing and identifying cryptic or sibling species where conventional methods are unable to resolve systematic problems.