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Aspects of physiology and trichome chemistry in the medicinal plant Tanacetum parthenium (L.) Schultz-Bip. Usher, Kevin Bernard

Abstract

This study investigated aspects of physiology and terpenoid chemistry in feverfew, a medicinal plant used for migraine therapy. The sesquiterpene lactone parthenolide accumulates in feverfew shoots and is thought to contribute to feverfew's antimigraine activity. The first part of this study examined the effects of nitrogen application and irrigation on shoot yield and shoot parthenolide concentration. Reduced shoot yield was observed under treatments of low nitrogen application and irrigation frequency. Leaf parthenolide concentration increased in plants grown with high nitrogen application rates and decreased with high irrigation rates. In the second part of this study, shoot yield, parthenolide concentration and trichome distribution were examined in response to developmental changes. Days longer than approximately 12 hours induced flowering. Feverfew grown under days shorter than 12 hours for extended periods remained in a vegetative stage and their leaves accumulated parthenolide in concentrations up to 10x that of flowering plants. Yield was lower in vegetative plants grown under short days but leaf to stem ratio was high. Glandular trichomes are the site of parthenolide biosynthesis and storage. Leaf parthenolide concentration is related to glandular trichome densities on leaf surfaces. Young leaves of vegetative plants have high trichome densities while young leaves of flowering plants have low trichome densities. Trichome densities decreased with leaf expansion and as density decreased, parthenolide concentration decreased. The third part of this study investigated the two terpenoid biosynthetic pathways involved in parthenolide biosynthesis. Experiments using ¹⁴C and ¹³C labeled substrates revealed that both the mevalonate (MEV) and methylerythritol phosphate (MEP) pathways contribute isoprene subunits to parthenolide biosynthesis. Two of the three isoprene subunits in parthenolide were enriched after feeding shoots 1-¹³Cmevalonate and 2-¹³C-acetate, an enrichment pattern consistent with the M E V pathway. Parthenolide's enrichment pattern after feeding 2-¹³C-pyruvate and 1- ¹³C-Glucose was consistent with isoprene contributions from both pathways. After feeding 2-¹³C-pyruvate however, there was a higher proportion of ¹³C-enrichment from the MEP pathway than from the MEV pathway.

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