Sexual hybrids of Tanacetum: biochemical, cytological and pharmacological characterization

Novel sexual hybrids have been produced between the medicinally-important s pecies T. parthenium (L.) Schultz-Bip. (feverfew) and T. vulgare (L.) Schul tz-Bip. (tansy). Morphologically, the F-1 hybrids were more closely aligned to feverfew than to tansy, although notable differences were observed in f loral and leaf morphologies of the hybrid plants compared to both parental species. Ultrastructurally, the lower epidermal leaf surfaces of the F-1 hy brids displayed characteristics from both parents, with glandular trichome morphology and density similar to that of feverfew, but non-glandular trich ome density comparable to that of tansy. Diploid F-1 (2n = 2x = 18) hybrids and their parental progenitors were analysed biochemically, using chromato graphic techniques. The bioactive germacranolide, parthenolide, was present in high concentrations [1.72+/-0.16% dry leaf weight (mean +/-s.d., n = 5) ] in leaf extracts from feverfew, but to a much lesser extent in both tansy and the F-1 hybrids (<0.03% and <0.01% dry leaf weight, respectively). Whi lst secondary metabolite accumulation in the leaves of the F-1 hybrids was largely additive compared to the parental species, novel compounds were als o detected in the F-1 hybrids by HPLC, GC and TLC, indicating the expressio n of new metabolic pathways as a result of sexual hybridization. Pharmacolo gically, leaf extracts from the F-1 hybrids inhibited human polymorphonucle ar leucocyte (PMNL) activity in vitro, despite containing only trace amount s of parthenolide, the principal bioactive moiety from feverfew. This, in c onjunction with the isolation of a fraction from the crude F-1 leaf extract displaying significant (>5%) inhibition of PMNL activity, provides further evidence that parthenolide is not the sole determinant of pharmacological activity in the genus Tanacetum.