J.L.S. Taylor

Towards the scientific validation of traditional medicinal plants

A large proportion of the population of developing countries usestraditional medicine alone, or in combination with Western drugs to treat awide variety of ailments. There has seldom been effective collaborationbetween the traditional and Western medical practitioners, largely due tothe perception that the use of traditional and herbal medicines has noscientific basis. With the renewed interest from Western countries in herbalremedies, and the increasingly urgent need to develop new effective drugs,traditionally used medicinal plants have recently received the attention ofthe pharmaceutical and scientific communities. This involves the isolationand identification of the secondary metabolites produced by the plants andused as the active principles in medical preparations. Research into thescientific validation of southern African medicinal plants used in thetreatment of pain and inflammation, hypertension and parasitic diseasesincluding those with anthelmintic, anti-amoebic, anti-bacterial and anti-bilharzia activity, is the current focus of studies conducted at the ResearchCentre for Plant Growth and Development.

Plant part substitution - a way to conserve endangered medicinal plants?

Population growth, urbanization and the unrestricted collection of medicinal plants from the wild is resulting in an over-exploitation of natural resources in southern Africa. Therefore, the management of traditional medicinal plant resources has become a matter of urgency. In southern Africa the most frequently used medicinal plants are slow-growing forest trees, bulbous and tuberous plants, with bark and underground parts being the parts mainly utilized. A strategy which would satisfy the requirements of sustainable harvesting, yet simultaneously provide for primary health care needs, would be the substitution of bark or underground parts with leaves of the same plant. This paper outlines the concept of plant substitution, using preliminary results of our recent investigations into four of the most important and most threatened South African medicinal plants - Eucomis autumnalis (bulb), Siphonochilus aethiopicus (rhizome), Ocotea bullata (bark), and Warburgia salutaris (bark) - as a demonstration of the kind of research necessary. Extracts of various plant parts were compared chemically using TLC-analysis, and pharmacologically in terms of antibacterial activity and cyclooxygenase-1 inhibition in vitro. The importance of the concept of plant part substitution as a strategy for the conservation of medicinal plants in southern Africa is discussed in terms of the results obtained.

Investigation of the antimutagenic effects of selected South African medicinal plant extracts

Dichloromethane extracts from different parts of Rhamnus prinoides, Ornithogalum longibracteatum, Gardenia volkensii, Spirostachys africana, Diospyros whyteana, Syzigium cordatum and Prunus africana were investigated for mutagenic and antimutagenic effects in Salmonella/microsome and micronucleus tests. None of the extracts tested in the Ames test were found to induce mutations or to modify the effect of the mutagen 4-nitroquinoline-oxide (4NQO). In the micronucleus test, extracts from twigs/bark of R. prinoides, twigs of D. whyteana, P. africana and S. cordatum significantly lowered the effect of the mutagen mitomycin C (MMC). Extracts from twigs/bark of G. volkensii and S. africana were genotoxic in the micronucleus test, while extracts of O. longibracteatum leaves potentiated the genotoxicity of MMC. This preliminary investigation shows that plant extracts used in traditional medicine may have particular effects with regard to mutagenicity and antimutagenicity indicating careful use in some instances and the need to isolate their active principles for further research.

Root initiation in Vigna radiata (L.) Wilczek hypocotyl cuttings is stimulated by smoke-derived extracts

Aqueous extracts of smoke, derived from Themeda triandra, a fire-climax grass, and Passerina vulgaris, a fynbos plant, stimulated root initiation and development in the hypocotyls of mung beans. Immersion time and the dilution of the smoke extracts were important in optimising the rooting response.

Plant-derived smoke solutions stimulate the growth of Lycopersicon esculentum roots in vitro

Aqueous extracts of smoke, derived from Themeda triandra, a fire-climax grass, and Passerina vulgaris, a fynbos plant, stimulated the growth of primary root sections of tomato roots in suspension culture. The optimal dilution for both extracts was 1:2000. Several of the fractions obtained from TLC separation of the Themeda and the Passerina extracts significantly promoted primary root growth. The auxins naphthaleneacetic acid (NAA), indolebutyric acid (IBA) and indoleacetic acid (IAA) were found to stimulate the growth of the primary root axis, with IAA and NAA significantly promoting lateral root number. Similarly, the naturally occurring cytokinins, zeatin and its derivatives (zeatin-O-glucoside; dihydrozeatin and zeatin riboside) stimulated primary root length. Zeatin and dihydrozeatin promoted secondary root growth, but only at very low concentrations.

THE EFFECT OF AGE, SEASON AND GROWTH CONDITIONS ON ANTI INFLAMMATORY ACTIVITY IN EUCOMIS AUTUMNALIS (MILL.) CHITT. PLANT EXTRACTS.

Eucomis (Family Hyacinthaceae) bulbs are greatly valued in traditionalmedicine for the treatment of a variety of ailments, predominantly thoseinvolving pain, fever and inflammation. The COX-1 assay was used to screenethanolic extracts prepared from the dried leaves, bulbs and roots of E. autumnalis (subspecies autumnalis) to determine the variation ofanti-inflammatory activity with age and season of harvest. Young plantswere found to have large amounts of COX-1 inhibitory activity, particularlyin the leaves. As the plant matured, greater activity was associated with thebulb and root extracts. The anti-inflammatory activity of the leaf, bulb androot extracts varied slightly throughout the year, with the greatest levelsdetected towards the end of the growing season, shortly before the onsetof dormancy. A seaweed application (Kelpak) decreased the anti-inflammatory activity of the leaf, bulb and root extracts, while increasedtemperature/increased light intensity had no significant effect on theCOX-1 inhibitory activity of the leaf extracts. The bulb extracts fromtreated plants harvested towards the end of the growing season showed asignificant decrease in anti-inflammatory activity, while the anti-inflammatory activity of the corresponding not root extracts increased.

COX-1 and COX-2 inhibitory activity in extracts prepared from Eucomis species, with further reference to extracts from E. autumnalis autumnalis

Prostaglandins are important mediators of the body’s response to pain and inflammation, and are formed from essential fatty acids found in cell membranes. This reaction is catalysed by cyclooxygenase, a membrane-associated enzyme occurring in two isoforms, COX-1 and COX-2. Non-steroidal anti-inflammatory drugs (NSAIDs) act by inhibiting the activity of COX. The investigation of Eucomis species (a popular South African medicinal plant) for potential anti-inflammatory activity showed high levels of COX-1 and -2 inhibitory activity associated with several species, specifically E. autumnalis and E. humilis. Further investigation was conducted using E. autumnalis subspecies autumnalis, as this is the species that is most widely utilised by traditional healers in southern Africa. The bulb extracts from this species were characterised by higher IC50 values for both COX-1 and COX-2 inhibition than obtained for the leaf and root extracts. The ratio of COX-2/COX-1 inhibitory activity was, however, similar to that of the root extracts, both values being less than one. The leaf extracts showed higher COX-1 than COX-2 inhibitory activity, with a ratio of 1.9. Most traditional remedies utilising Eucomis, are prepared from the bulbs (possibly including some root material) of this species.

In vitro propagation of Eucomis L'Hérit species - plants with medicinal and horticultural potential

Eucomis (Family Hyacinthaceae) are deciduousgeophytes with long, narrow leaves and erect, densely packed flower spikes. Thebulbs are greatly valued in traditional medicine for the treatment of a variety ofailments, and are thus heavily harvested for trade in South Africas traditional herbal markets. Eucomis species propagaterelatively slowly from offsets and seed, and this, together with theirover-utilisation ethnopharmacologically, has led to their threatened status. Thein vitro propagation of the genusEucomis was investigated to optimise this technique for thebulk production of plants for commercial and conservation purposes. Multipleshoot production was initiated from leaf explants, in all species studied. AMurashige and Skoog (MS) medium, supplemented with 100mg amp;ell;−1 myo-inositol, 20g amp;ell;−1 sucrose, and solidified with 2g amp;ell;−1 Gelrite® was used. Theoptimal hormone combination for shoot initiation in the majority of species was1 mg amp;ell;−1 NAA and 1mg amp;ell;−1 BA. Optimal root initiation wasdemonstrated on media supplemented with 1mg amp;ell;−1 IAA, IBA or NAA, depending onspecies. A continuous culture system using this protocol produced 25–30plantlets per culture bottle, with 10–25 specimens per bottle availablefor acclimatisation. To maximise plantlet survival, different support media usedduring the acclimatisation process were necessary. Certain species respondedbest on a vermiculite medium, while perlite (which holds less water) wasnecessary for the optimal survival rate of other species. Acclimatised plantletswere repotted in a sand: soil mix (1:1).

The effect of nitrogen and sucrose concentrations on the growth of Eucomis autumnalis (Mill.) Chitt. plantlets in vitro, and on subsequent anti-inflammatory activity in extracts prepared from the plantlets

Large amounts of anti-inflammatory activity are present in extractsprepared from Eucomis plants. Extracts prepared from in vitroplantlets grown on a modified Murashige and Skoog medium supplementedwith 1 mg &ell−1 NAA and 1 mg &ell−1 BA, were tested intwo cyclooxygenase assays (COX-1 and COX-2). Ethanol extracts showedhigh levels of COX-1 and COX-2 inhibitory activity, with a COX-2/COX-1inhibition ratio of 1.1. Further experimental work aimed to determine thefactors affecting the accumulation of anti-inflammatory compounds inin vitro plantlets. High concentrations of sucrose (40 g &a,p;ell−1) inthe culture medium significantly increased the number of shoots initiated,but had no effect on the subsequent anti-inflammatory activity. Lowconcentrations of sucrose (10 g &ell−1) led to a significantdecrease in COX-1 inhibition. Changig the amount of nitrogen in the medium(but not the ratio of nitrate to ammonium ions) had no significant effect onthe COX-1 inhibitory activity of the extracts.

Variation in the level and type of cytokinin with the stage of root development in Impatiens wallerana Hook. f. stem cuttings

The cytokinin content of the basal portion of stem cuttings of Impatiens wallerana was examined daily. Both qualitative and quantitative changes were observed in the levels of cytokinin-like compounds over the period of root formation in the stem cuttings. The peak in polar cyokinin-like activity coincided with the initial stages of root primordia initiation and development. Non-polar cytokinin-like activity showed greater fluctuations but only exhibited a substantial increase after the roots had extended through the epidermis and had begun to elongate. It is probable that it is the metabolic ability of the stem tissue to alter the initial levels of hormones present that enables efficient adventitious root formation.