Comparing metabolomes: The chemical consequences of hybridization in plants

• Hybridization may lead to unique phytochemical expression in plant individuals. Hybrids may express novel combinations or extreme concentrations of secondary metabolites or, in some cases, produce metabolites novel to both parental species. • Here we test whether there is evidence for extreme metabolite expression or novelty in F₁ hybrids between Senecio aquaticus and Senecio jacobaea. Hybridization is thought to occur frequently within Senecio, and hybridization might facilitate secondary metabolite diversification within this genus. • Parental species express different quantities of several classes of compounds known to be involved in antiherbivore defence, including pyrrolizidine alkaloids, chlorogenic acid, flavonoids and benzoquinoids. Hybrids demonstrate differential expression of some metabolites, producing lower concentrations of amino acids, and perhaps flavonoids, than either parental species. Despite evidence for quantitative hybrid novelty in this system, NMR profiling did not detect any novel compounds among the plant groups studied. • Metabolomic profiling is a useful technique for identifying qualitative changes in major metabolites according to plant species and/or genotype, but is less useful for identifying small differences between plant groups, or differences in compounds expressed in low concentrations.