Variation of sesquiterpene lactone contents in Lactuca georgica natural populations from Armenia

A comparative phytochemical study of seven sesquiterpene lactones in natural populations of the wild lettuce Lactuca georgica Grossh. (Asteraceae) was performed, based on 17 accessions derived from seven localities representing three regions in Armenia. The compounds were profiled and quantified in roots and leaves of the plants, grown from achenes (cypselas) in a glasshouse under controlled conditions. The contents of major sesquiterpene lactones were estimated in the plant materials by HPLC/PDA, including the germacranolide glucoside—lactuside A and the guaianolides: lactucin, 11β,13-dihydrolactucin, its three esters (at C-8) with acetic, p-hydroxyphenylacetic and methacrylic acids and its 15-O-glucoside (cichorioside B). The plant roots could be characterized by the occurrence of lactuside A and two 11β,13-dihydrolactucin derivatives (acetate and methacrylate) in relatively high amounts. Lactucin and 11β,13-dihydrolactucin were major sesquiterpene constituents in the plant leaves. An analysis of quantitative results of these seven constituents led to the following conclusions: (1) the sesquiterpene lactone contents varied widely, mostly between-populations for root samples, but mostly within-populations for leaf samples, (2) these differences are likely to be genetically controlled since all accessions were grown under standardized glasshouse conditions. This study is probably the first report of detailed screening of L. georgica natural populations and individuals for any trait. The obtained results show that L. georgica, a species within the primary lettuce gene pool, should be considered as an attractive source of germplasm in further research and improvement of cultivated lettuce (Lactuca sativa).