Production of toxic pavettamine and pavettamine conjugates in the gousiekte-causing Fadogia homblei plant and its relation to the bacterial endosymbiont

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 -2 -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.

Distribution of the cardiotoxin pavettamine in the coffee family (Rubiaceae) and its significance for gousiekte, a fatal poisoning of ruminants

“…At present it is not known whether the endosymbiont plays any role in the production of the poisonous compound. Analysis of in vitro cultures of the Fadogia homblei endosymbiont, however, did not reveal production of pavettamine [15].…”

“…The potential presence and concentration of pavettamine were determined through detection by tandem mass spectrometry after derivatization with benzoyl chloride and separation by ultra-performance liquid chromatography (UPLC TM ) [15]. The selected plants, 82 taxa from 14 genera, are from the Rubiaceae since gousiekte has invariably been associated with plants of this family [4,16].…”

“…Plant taxa, in which pavettamine was detected, are listed in Table 1. Wild collected 374 ± 13* a value adopted from Van Elst et al [15] b species with leaf nodules c species with non-nodulating bacterial endophytes Two additional species were found to be positive for the toxin, namely Psychotria kirkii and Ps. viridiflora.…”

“…Furthermore, a threshold concentration of pavettamine in leaves has not been determined for causing the onset of the development of gousiekte. The mass spectrometry method for the quantification of pavettamine as described by Van Elst et al [15] allows the detection of several other important polyamines (diaminopropane, putrescine, cadaverine, spermidine, spermine and agmatine) alongside pavettamine in biological samples. Pavettamine certainly is an unusual polyamine and of the common plant polyamines most closely resembles cadaverine (see Figure 1), both having a carbon chain of five carbon atoms.…”

“…However, this method does not quantify the concentration of pavettamine and, as the authors stated, the procedure is tedious. Recently, a mass spectrometry based method for the analysis of pavettamine was reported [15]. It allows detection and quantification of pavettamine in biological samples in a fast and sensitive manner without the need for large sample volumes.…”