(1990)demonstrated the induction of an anti-fungal guaianolide sesquiterpene lactone in chicory upon infection with Pseudomonas cichorii. These sesquiterpene lactones were shown to have significant anti-feedant activity ( Rees and Harborne, 1985). (tap) roots, leaves, and stems and also in the etiolated heads, which are eaten as a vegetable in some parts of the world ( Rees and Harborne, 1985 Beek et al., 1990 Price et al., 1990). The chicory ( Cichorium intybus) plant contains bitter sesquiterpene lactones, such as lactucin, 8-deoxylactucin, and lactupicrin, in most of its organs e.g. The possible involvement of a number of amino acids in sesquiterpene synthase product specificity is discussed. Finally, the two deduced amino acid sequences were modeled, and the resulting protein models were compared with the crystal structure of tobacco ( Nicotiana tabacum) 5- epi-aristolochene synthase, which forms germacrene A as an enzyme-bound intermediate en route to 5- epi-aristolochene.

coli were similar to the values reported for the GAS protein that was recently purified from chicory roots. The K m value, pH optimum, and MonoQ elution volume of one of the proteins produced in E. On MonoQ, these proteins co-eluted with the two heterologously produced proteins. Protein isolation and partial purification from chicory heads demonstrated the presence of two GAS proteins. Northern analysis demonstrated that both genes were expressed in all chicory tissues tested albeit at varying levels. Heterologous expression of the genes in Escherichia coli has shown that they both catalyze exclusively the formation of (+)-germacrene A, making this the first report, to our knowledge, on the isolation of (+)-germacrene A synthase (GAS)-encoding genes. Using polymerase chain reaction with degenerate primers, we have isolated two sesquiterpene synthases from chicory that exhibited 72% amino acid identity. Germacrene A is of interest because of its key role in sesquiterpene lactone biosynthesis and because it is an enzyme-bound intermediate in the biosynthesis of a number of phytoalexins.

Chicory ( Cichorium intybus) sesquiterpene lactones were recently shown to be derived from a common sesquiterpene intermediate, (+)-germacrene A.

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