Graduate Thesis Or Dissertation
 

The biosynthesis of terpenes in Pelargonium graveolens

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  • Pelargonium graveolens Ait., rose geranium, contains several oxygenated monoterpenes, most of which are related to each other structurally. In this work, the metabolism and interconversions of these terpenes was investigated. A chromatographic analysis of geranium oil was performed initially for the purposes of identifying the terpenes and determining which chromatographic method was most desirable for this work. It was found that gas-liquid chromatography was superior to thin layer chromatography both in resolution and in affording a convenient and sensitive method of counting radioactivity. Three types of experiment were used in attacking this problem: (1) Variations in terpene synthesizing ability with leaf age were noted in order to determine the site of most active biosynthesis. (2) Leaves were exposed to C¹⁴O₂ in light for periodically increasing time intervals, and samples were taken at those intervals. The radioactive terpenes were extracted, and were separated by means of gas-liquid chromatography, and the terpene fractions were counted in a liquid scintillation counter. (3) Isolated carbon-14 labeled terpenes were used as substrates in interconversion reactions by placing them in contact with sliced or minced geranium leaves in the light. From the above, it was determined that the interconversions of the terpenes of geranium are very rapid and proceed through the biosynthetic pathway mainly by a series of reductions. It was also shown that the biosynthesis of terpenes is very active only in those leaves that are still expanding. Besides the above, two types that were not directly related to the interconversion problem Because it is a widely postulated precursor of terpenes, the incorporation of mevalonic acid into the terpenes of geranium was attempted, and possible incorporation of mevalonic acid-2-C¹⁴ into geraniol-citronellol, citral, and a fraction which migrates to the solvent front in thin layer chromatography was observed. Studies were performed to develop methods of obtaining enzymatically active cell-free extracts from monoterpene producing plants. The enzyme activities extracted were glutamyl transferase (from Mentha piperita, peppermint, Mentha puleqium, pennyroyal, and geranium), mevalonic kinase (from peppermint), and an enzyme activity which possibly produced piperitenone, a monoterpene of peppermint and pennyroyal, using mevalonic acid-2-C¹⁴ as the substrate and extracts of either peppermint or pennyroyal as the enzyme system.
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