Medicinal Plants at the Ethnobotany–Biotechnology Interface in Africa
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South African Journal of Botany 2004, 70(1): 89–96 Copyright © NISC Pty Ltd Printed in South Africa — All rights reserved SOUTH AFRICAN JOURNAL OF BOTANY EISSN 1727–9321 Medicinal plants at the ethnobotany–biotechnology interface in Africa SA Nigro1, NP Makunga1* and OM Grace2 1 Research Centre for Plant Growth and Development, School of Botany and Zoology, University of KwaZulu-Natal Pietermaritzburg, Private Bag X01, Scottsville 3209, South Africa 2 Ethnobotany Unit, National Botanical Institute, PO Box 52099, Berea Road, Durban 4007, South Africa * Corresponding author, e-mail: [email protected] Received 5 September 2003, accepted 15 October 2003 Africa bears a long history of people–plant interaction useful plants. African ethnomedicinal plants with valu- that has been significantly enhanced by biotechnology. able secondary metabolites and established in vitro Ethnomedicinal plants have been targeted in the search propagation protocols may be likely candidates for for new natural products but their exploitation has led to genetic transformation when biotechnology becomes concern for their conservation. Biotechnology has more accessible on the continent. The ethnic and floral applications that extend beyond conservation to opti- wealth of southern Africa lends a prime example of how mising natural product research and adding value to biotechnology may enrich people–plant interactions. Introduction Africa, the cradle of mankind, bears a long history of people- commercial value (Coombes 1986), biotechnology is an plant interaction. It is the second largest of the earth’s seven important instrument for the manipulation of plants to better continents, and is characterised by rich ethnic and biotic suit the needs of Man. In adding value to useful plants, it mosaics that represent 13% of the earth’s human population plays a developmental role at the interface of ethno- and and the largest of continental floras, estimates of which economic botany. The term was first applied by the range between 50 000 and 70 000 plant taxa (Klopper et al. Hungarian engineer Karl Ereky in 1917 to ‘all lines of work 2002, Smith and Van Wyk 2002). The African flora is remark- by which products are produced from raw materials with the able not only for its diversity but its distinctiveness: as many aid of living things’ (Glick and Pasternak 1994). Although as 88% of its species are endemic (Davis et al. 1994). High biotechnology referred originally to a system for the large- levels of endemism indicate that many of the continent’s scale production of pigs, the term was used loosely until plant resources are uniquely African. the establishment of the journal Biotechnology and The terms ‘ethno-’ and ‘economic’ botany to describe the Bioengineering in 1961. Biotechnology was redefined as the study of people–plant interaction have been used inter- ‘industrial production of goods and services using biological changeably and deserve clarification. We refer to Wickens organisms, systems, and processes’ within the disciplines of (1990) who defined ethnobotany as ‘the study of useful microbiology, biochemistry and chemical engineering (Glick plants prior to their commercial exploitation and eventual and Pasternak 1994). The discovery of recombinant DNA domestication’, and economic botany as an umbrella term technology in 1973 (Cohen et al. 1973) introduced biotech- applied to ‘the study of plants utilised either directly or indi- nology at the molecular level, where an organism’s machin- rectly for the benefit of Man’. Economic plants therefore ery could be modified to manufacture desired products. include those used in agriculture, horticulture and forestry The ethnobotanical approach to natural products research (Wickens 1990) and in turn provide for the many industries highlights that those plant taxa used traditionally are most that make use of plant products. In Africa, where approxi- likely to yield useful products, and, consequently, are most mately 43% of the population are impoverished (Africa South likely to be threatened by over-exploitation (Grace et al. of the Sahara 2001), the same plant species may be used at 2002). It is not surprising, therefore, that useful plant species all levels between subsistence and commercial agriculture, have been targeted in the search for and optimisation of new thus blurring the definition of ‘ethno-’ and ‘economic’ plants. natural products, or that the value added to them using The transitory process of a useful plant species assuming biotechnology has strengthened the call for their conserva- commercial importance has been enhanced significantly in tion. Of the multitude of purposes for which Man exploits modern times by biotechnology. Described as the use of bio- plants, their use in ethnomedicine is among the most rele- logical entities to create products with novel functions or vant to modern society. Ethnomedicinal plants have con- 90 Nigro, Makunga and Grace tributed many important phytochemicals to allopathic medi- ing the same period (Bajaj 1988–1997). Progress was made cine. African examples include molluscicides from in particular on in vitro techniques such as micropropaga- Phytolacca octandra L. (Phytolaccaceae) used to control the tion, induction of high yielding somaclones, protoplast fusion schistosomiasis vector (Lemma 1991 cited in Horeau and for the induction of novel somatic hybrids, cyropreservation DaSilva 1999), and several compounds from Catharanthus of germplasm, and Agrobacterium rhizogenes-mediated roseus G.Don (Apocynaceae) used in therapy of diabetes transformation for hairy roots (Bajaj 1998). and tumours (George et al. 2001). Familiar plant products The main objectives of such research are to enhance the with African origins include Old World cotton (Gossypium production of secondary metabolites, by manipulating plant herbaceum L., Malvaceae), coffee (Coffea spp., cells to increase metabolic flux into specific pathways (Dixon Rubiaceae), and frankincense (Boswellia papyrifera (Del.) and Bolwell 1986). Since many widely used natural products Hocsht, Burseraceae) (Geldenhuys and Van Wyk 2002). are remarkably complex in structure, and despite advances In this paper we consider the role of biotechnology at the in synthetic chemistry, synthesis is frequently difficult and interface of ethno- and economic botany in Africa. We review economically non-viable (Hamill and Lidgett 1997). Indeed, progress made in the disciplines over recent decades, and plants remain the major sources of a variety of indispensa- speculate on the way forward, with particular reference to ble industrial compounds, examples of which include phar- the search for natural products from ethnomedicinal plants in maceuticals (e.g. steroids, alkaloids), food additives (e.g. the southern African flora. emulsifiers, natural flavourants and colourants) (Balandrin and Klocke 1988, Bajaj and Ishimaru 1999) and, more Understanding Medicinal Plants recently, nutraceutics (Bourgaud et al. 2001). The documentation and study of people-plant interaction in Conserving the African Flora Africa began relatively recently with the arrival of European colonists (Van Wyk 2002). Ethnobotanical accounts of the Taxa used for their secondary metabolites on a commercial east African flora include those of Williamson (1955) and or industrial level may be considered ‘economic plants’, but Lindsay (1978). Burkhill’s (1985) volumes for West Tropical the material from which useful compounds are extracted is Africa are keystones for that region, as is Dounias’ review not always cultivated, or wild-harvested on a sustainable (2000) for Central and West Africa. Plant use throughout the basis. A case in point is Prunus africana (Hook.f.) Kalkm. continent was considered recently by Iwu (1993) and (Rosaceae) bark, from which several secondary metabolites Neuwinger (2000), and continues to be documented by pro- are extracted for use in European pharmaceuticals. The grammes such as the Survey of Economic Plants for Arid principal sources of the bark are natural forest populations in and Semi-Arid Lands (SEPASAL) (Davis et al. 1998, SEPA- Africa and Madagascar and, despite legislation to ensure SAL 2003). otherwise, harvesting is non-sustainable (Cunningham and The history of ethnobotanical research in southern Africa Mbenkum 1993, Prunus Net 2003). was thoroughly reviewed by Van Wyk (2002), but a literature A similar situation affects ethnomedicinal plant taxa in search of English sources will yield several key publications southern Africa; they are almost exclusively wild-harvested (Grace et al. 2002). Ethnomedicinal plants in southern Africa to meet the demands of a booming informal trade and con- were accounted for in the famous tome of Watt and Breyer- sumer industry (see, for example, Cunningham 1988, Brandwijk (1962), and proceeded by those of, for example, Mander 1998, Williams et al. 2000). Germplasm conserva- Mabogo (1990), Hutchings et al. (1996), Van Wyk et al. tion, including propagation and breeding to improve various (1997) and Arnold et al. (2002). Concern for the conserva- traits (Nessler 1994), and cryopreservation, is focussed on tion of medicinal plants in recent decades stimulated crop plants but is equally relevant to wild-harvested medici- research that gave rise to a collection of cornerstone publi- nal taxa. This branch of conservation seeks to arrest genet- cations on their trade. Those dealing with southern Africa ic erosion in indigenous taxa (Bukenya-Ziraba 1998) that include Cunningham (1988), Scott-Shaw (1990), Mander