Abstract:
Plant poisoning of livestock is responsible for considerable economic losses in southern Africa.
Six plant species of the Rubiaceae family are known to cause gousiekte, a cardiac syndrome of
ruminants induced by ingestion of the toxic compound pavettamine. Progress in understanding
the aetiology of this disease is largely hampered by the variable toxicity of the plants and the absence of a quantification method for pavettamine. The pavettamine concentration in leaf
samples of Fadogia homblei, a known gousiekte causing plant, was analyzed by massspectrometry.
In the most apical leaf pair, the highest concentration of pavettamine was
detected. Distal leaves contained progressively less pavettamine. Besides a significant amount
of free pavettamine, most pavettamine was found to occur in a conjugated form. To which
molecules the pavettamine is conjugated remains unknown as is the function of conjugated
pavettamine in the development of gousiekte. All know gousiekte-causing plants contain
symbiotic bacteria in their leaves; it was hypothesized that these bacteria might be involved in
the production of pavettamine. However, analysis of in vitro cultures of the Fadogia homblei
endosymbiont revealed no production of pavettamine. Pavettamine is therefore not produced
by the bacteria alone. It is either the product of the interaction with the plant or solely produced
by the host.
