Pyrrolizidine alkaloid composition in the plant and its interaction with the soil microbial community

Abstract

Plants are attacked by a variety of (micro)organisms. In order to cope with potential attackers many plants synthesize a diversity of repellent, deterrent and/or toxic compounds. Pyrrolizidine alkaloids (PAs) are a well-known class of defense compounds, abundantly found in species of Senecio and Jacobaea. The objectives of the study were to acquire knowledge on the PA composition of plants and its interaction with soil-borne microorganisms. In order to do so, a more sensitive, PA-analysing method was applied, which allowed us to distinguish between PAs in tertiary amine and N-oxide form. The tertiary PA form is known to have a more negative effect on generalist insects. Our study clearly showed that high levels of tertiary PAs occur in Jacobaea vulgaris and not caused by an artefact as suggested in previous studies. Green-house experiments showed that the PA composition below- and aboveground was significantly aff ected by both soil-type and soil-inoculum. The inoculum-induced PA composition aboveground did affect thrips resistance for one J. vulgaris genotype. Experiments also showed that the fungal community did depend on the PA composition of the plant while this had less or no effect on bacterial and mycorrhizal communities in roots and rhizosphere soil.