Genetic and chemical variation in North American populations of the medicinal plant wild tarragon (Artemisia racunculus L.).

摘要

Artemisia dracunculus L. (wild tarragon; Asteraceae) is a polymorphic, herbaceous perennial with a distribution spanning western North America (NA), Eastern Europe and most of temperate Asia. Wild tarragon has been widely used as a folk remedy for numerous ailments and seven compounds (davidigenin, sakuranetin, 6-demethoxycapillarisin, 5-O-caffeoylquinic acid, 4,5-di-O-caffeoylquinic acid, 2',4-dihydroxy-4'-methoxydihydrochalcone and 2',4'-dihydroxy-4-methoxydihydrochalcone), previously isolated from the plant, have shown bioactivity in studies on type 2 diabetes. The species is known to have diploid to decaploid individuals and the production of some phytochemicals has been shown to vary between cytotypes. Focusing on populations in the U.S., four main areas were investigated, (1) the geographical distribution of cytotypes, (2) the influence of cytotype, environment, and genetics on qualitative and quantitative variation of the seven compounds, (3) essential oil diversity, and (4) genetic diversity and structuring of the populations. The main findings of these investigations were that diploids and polyploids were found in Eurasia, while only diploids were found in NA. In qualitative chemical investigations, decaploid plants were found to contain all the target compounds, while only sakuranetin, trace amounts of 6-demethoxycapillarisin, and complex mixtures of various caffeoylquinic and di-O-caffeoylquinic acids were detected in diploids from the U.S. In the quantitative analyses, sakuranetin levels varied between wild individuals and their cultivated clones, but the same four sites had the highest average production in both wild and common garden conditions. Essential oils extracted from NA populations represent a number of new chemotypes for the region. Primary components included (Z)-beta-ocimene, methyl eugenol, methyl chavicol and alpha-terpinolene. Many of the samples had significant concentrations of the phenylacetylenes capillene, 5-phenyl-1,3-pentadiyne and 1-(4-Methoxyphenyl)-2,4-pentadiyne. The isocoumarinic acetylene, capillarin, was also found in the majority of samples but in low amounts. Four different genetic diversity indices were calculated and all returned comparable values, with ∼78% genetic variation within populations and ∼22% of the variation between populations. In a cluster analysis, based on genetic distances, populations with high sakuranetin production were grouped together. In conclusion, ploidy level was correlated with the presence of medicinal compounds, while both genetics and environment were found to influence quantitative variation of sakuranetin.