Abstract
One of the most intriguing questions in chemical ecology is why one plant species produces so many different structural varieties of similar defence compounds. It has been postulated that these varieties originate from the ‘evolutionary arms-race’ between plants and their enemies. Because biological activity is strongly correlated with structure, single-step modifications may yield a compound that provides protection against an enemy that was hitherto insensitive. In Dutch populations we have found two naturally occurring chemotypes of Barbarea vulgaris: one produces mainly 2-phenylethyl-glucosinolate (gluconasturtiin) whereas the other produces mainly the hydroxylated form, S-2-OH-2-phenylethyl-glucosinolate (glucobarbarin). Due to this single hydroxy group, the compounds and their hydrolysis products may have completely different effects on phytophages and their natural enemies. Here we propose to analyse the molecular-genetic basis of this qualitative glucosinolate polymorphism in B. vulgaris and associate this to the ecological consequences for the plant. Based on sequence information from the close relative Arabidopsis thaliana, we will first analyse which gene/enzyme governs the difference between the two chemotypes and design a probe to link differences in gene expression to chemical profiles. Second, we will assess whether the two chemotypes differently affect generalist and specialist shoot-feeding aphids and root-feeding nematodes. Additionally, we will analyse how the natural enemies of the aphids are affected by the difference in glucosinolate type. Eventually, we will analyse whether there are other ecological costs involved by comparing both inter- and intraspecific competitive ability of the two chemotypes. By combining the molecular-genetic information with the ecological aspects of this chemical polymorphism, we will obtain a comprehensive understanding of several intrinsic and extrinsic processes that are fundamental to the evolution of plant chemical diversity.
Netherlands