Aspilia mossambicensis: In Vitro Propagation and Production of Antibiotic Polyacetylenes by Root Cultures

Abstract

Aspilia mossambicensis (Oliv.) Wild (Asteraceae), (Fig. 1) is widespread in central and eastern tropical Africa (Wild 1966), ranging from Ethiopia through east Africa, the Congo, Zambia, Zimbabwe, Malawi, Mozambique, and Transvaal to Natal (Hilliard 1977). Various folk uses of this and other Aspilia species have been reported, including its use as a remedy for cystitis and gonorrhoea (Kokwaro 1976; Burkill 1985), treatment of abdominal pains, intestinal worms, and skin infections (Rodriguez 1988). Previous reports for two other species of Aspilia (A. montevidencis and A. parvifolia) showed the presence of the tridecapentaynene derivative, thiophene A (I) (see Fig. 2 for structures), in roots (Bohlmann et al. 1973, 1981). Methanol and aqueous extracts of A. africana have recently been shown to have antibacterial activity against Gram-positive and Gram-negative bacteria, including Agrobacterium tumefaciens, at concentrations ranging from 0.1 to 0.5 g/ml (Macfoy and Cline 1990). Evidence that wild chimpanzees use A. mossambicensis as a dietary and medicinal supplement (Wrangham and Nishida 1983) suggested the possibility that the plant could have biocidal activity, and prompted an investigation of the phytochemistry of this species. Thiarubrines A and B (II, IV) and the monothiophenic derivatives, thiophenes A and B (I, III), were subsequently isolated from leaves of dried material (Rodriguez et al. 1985). Thiarubrine A has been found to exhibit strong antifungal activity towards the human pathogens Candida albicans and Aspergillus fumigatus at concentrations comparable to those of amphotericin B (Towers et al. 1985). Thiarubrine A and thiophene A have also been shown to be toxic to murine cytomegalovirus and Sindbls virus in the presence of ultraviolet radiation (Hudson et al. 1986a, b). In vitro studies conducted at Irvine indicate a concentration of 5 ppm of thiarubrine A is toxic to the nematode Meloidogyne javanica (Rodriguez 1988). This finding has been utilized in a joint project of researchers at Irvine and the University of California at Riverside, and further research has established that thiarubrine-containing plants can effectively suppress plant parasitic nematode infestation under field conditions, and thereby increase crop yields (ER, unpubl.).