Variation in pyrrolizidine alkaloid patterns of Senecio jacobaea
Ten pyrrolizidine alkaloids and four chemotypes are reported of vegetative plants of Senecio jacobaea populations and (clonal) families from across Europe.
Introduction
Plants from the genus Senecio (Asteraceae) are known for the production of a wide variety of pyrrolizidine alkaloids (PAs) (Hartmann and Witte, 1995) that have hepatotoxic and carcinogenic properties (Mattocks, 1968, Cheeke, 1988). In Senecio species PAs are produced in the roots as senecionine N-oxides (Hartmann & Toppel, 1987, Toppel et al., 1987). Senecionine N-oxide is transported via the phloem to the above ground plant organs (Hartmann et al., 1989) where it is transformed into several related PAs (Hartmann and Dierich, 1998). The transformation of senecionine into related PAs differs between Senecio species and hence species-specific PA patterns are produced (Hartmann and Dierich, 1998). Senecio jacobaea can contain more than 10 senecionine related alkaloids (Witte et al., 1992). PA concentration in S. jacobaea is partly genetically determined (Vrieling et al., 1993). Witte et al. (1992) described two PA chemotypes for S. jacobaea, the jacobine type and the erucifoline type, based on PA content in inflorescences of plants collected in the field. Jacobine types were characterized by the PAs jacobine and jacozine and lacked erucifoline, while the erucifoline types contained erucifoline and acetylerucifoline but hardly any jacobine (see Fig. 1 for structures). The two chemotypes did not differ in concentrations of other PAs such as senecivernine, senecionine, integerrimine and seneciphylline. Only rarely an intermediate chemotype was found that contained both jacobine and erucifoline. The patterns described by Witte et al. (1992) are interesting in relation to the evolution of diversity of alkaloids. However, generally only one plant per population was sampled and collected in its natural habitat. Therefore, it is not possible to disentangle environmentally induced patterns and genetic effects. Here, we investigated the PA patterns in leaves of vegetative plants from 10 European populations of S. jacobaea. To determine whether the different PA patterns have a genetic basis, we studied these patterns in cloned S. jacobaea genotypes and half-sib families grown under identical controlled conditions to minimize a possible effect of environment. To determine the variation within and between the different populations, PAs from 5 plants of every population were analyzed.
Section snippets
Variation in PA composition within clonal families
To show that variation in PA composition among plants is genetically determined, we studied the variation in PA profiles within 10 clonal families of S. jacobaea (16–34 plants per family). Each clonal family was from a different population (Table 1). In some plants 6 senecionine related PAs were found while other plants only contained two PAs. The PA composition (relative abundance) of each clonal family is shown in Fig. 2. Clonal families differed in relative percentages of senecionine,
Growth conditions
All plants were grown in 50/50 dune sand/peat mixture in 11 cm diameter pots in a growth chamber: photoperiod 8 h light: 16 h dark, 20 °C day/15 °C night, relative humidity 70%. After two months in the pots the plants were given ample nutrients.
Clonal families, half-sib families and populations
Clonal families: We used 16–34 plants per clonal family. A clonal family consisted of one randomly selected genotype of a population. This genotype was propagated via tissue culture. Plants were grown for two months in pots before analyzing the PA
Acknowledgements
We are most grateful to Dr. Jens Hagen, Dr. L. Witte and Prof. Dr. T. Hartmann for their help with the GC and GC–MS analysis. We thank Helene de Vos and Karin van Veen- van Wijk for their technical assistance and Martin Brittijn for the artwork. Urs Schaffner, Stefan Andersson, Els Schlatmann, Henk van Dijk, Nico de Boer and the Botanical Garden in Copenhagen generously provided us with seeds from the different populations. We thank Nicole van Dam, Ed van der Meijden and two anonymous referees
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