Variation of pyrrolizidine alkaloids in Senecio vulgaris plants from native and invasive ranges

Pyrrolizidine alkaloids (PAs), a typical kind of secondary metabolites in plants, have important roles on defense against herbivores and pathogens; however, specialist herbivores adapted to PAs can use them as cues for oviposition and feeding. Thus, in the native ranges, PA diversity and concentration in plants were selected by the balance between pressure from generalist and specialist herbivores. In introduced ranges, where the specialist herbivores are absent, the introduced plants could increase concentration and diversity of PAs. This predication is deduced from the Shift Defense Hypothesis (SDH). In this research, we investigated whether there were any differences between native and invasive Senecio vulgaris plants (from Europe and China, respectively) with regards to the PA composition and concentration. We grew the native and invasive S. vulgaris plants in an identical condition and harvested them when they started to bloom. Their roots and shoots were separately harvested and dried. PA composition and concentration from powder of the shoots and roots were detected by using liquid chromatography – tanderm mass spectrometry (LC-MS/MS). We identified 14 PAs which belongs to the structural group senecionine – like PAs. Most of them occurred in both the native and invasive S. vulgaris plants, except the usaramine N – oxide that was only found in the native ones. From the 14 PAs identified, only riddelliine N – oxide had significantly higher present frequency in the invasive plants than in the native plants. The invasive S. vulgaris plants had significantly lower concentration of 3 individual PAs (seneciphylline N – oxide, spartioidine and spartioidine N – oxide) than the native ones. These results demonstrated that PA diversity and concentration of some individual PAs tended to reduce in the invasive range of S. vulgaris. This is contrary to the predictions of the SDH that the invasive plants would produce more qualitative defense than the native ones, and it is probably an evidence that a little trade – off between defense and growth happened to the S. vulgaris in China.