Biosynthesis of costunolide, dihydrocostunolide and leucodin. Demonstration of cytochrome P450-catalyzed formation of the lactone ring present in sesquiterpene lactones of chicory - de Kraker,J.-W.; Franssen,M.CR.; Joerink,M.; de Groot,A.; Bouwmeester,H.J. (Plant Physiol, 2002)