Sexual hybrids of Tanacetum: biochemical, cytological and pharmacological characterization

Abstract

Novel sexual hybrids have been produced between the medicinally-important species T. parthenium (L.) Schultz-Bip. (feverfew) and T. vulgare (L.) Schultz-Bip. (tansy). Morphologically, the F1 hybrids were more closely aligned to feverfew than to tansy, although notable differences were observed in floral and leaf morphologies of the hybrid plants compared to both parental species. Ultrastructurally, the lower epidermal leaf surfaces of the F1 hybrids displayed characteristics from both parents, with glandular trichome morphology and density similar to that of feverfew, but non-glandular trichome density comparable to that of tansy. Diploid F1 (2n = 2× = 18) hybrids and their parental progenitors were analysed biochemically, using chromatographic 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 F1 hybrids (<0.03% and <0.01% dry leaf weight, respectively). Whilst secondary metabolite accumulation in the leaves of the F1 hybrids was largely additive compared to the parental species, novel compounds were also detected in the F1 hybrids by HPLC, GC and TLC, indicating the expression of new metabolic pathways as a result of sexual hybridization. Pharmacologically, leaf extracts from the F1 hybrids inhibited human polymorphonuclear leucocyte (PMNL) activity in vitro, despite containing only trace amounts of parthenolide, the principal bioactive moiety from feverfew. This, in conjunction with the isolation of a fraction from the crude F1 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.