Observations on the Nature and Biosynthesis of Terpenoid Quinones and Related Compounds in Tobacco Shoots

Abstract

Tobacco shoots have been shown to contain phylloquinone, plastoquinone, “plastoquinone C”, “plastoquinone D”, α‐tocopherol, α‐tocopher lquinone and ubiquinone‐10. 2. The levels of all these components increased as the green leaves aged. In senescent leaves chlorophyll, β‐carotene, phylloquinone and ubiquinone were absent; plastoquinone, “plastoquinone C” and “plastoquinone D” on the other hand were present in large amounts. 3. Two dimensional thin layer chromatography showed that the “plastoquinone C” and “plastoquinone D” preparations each consisted of three quinone components having ultraviolet spectra qualitatively identical to that of plastoquinone. 4. The ultraviolet, infrared, nuclear magnetic resonance and mass spectra of a “plastoquinone C” preparation indicated that this group of quinones were monohydroxy‐plastoquinone‐9′s; the hydroxyl group in each case being located in one of the isoprene units numbers 2–8 of the nonaprenyl side chain, i. e., not the first or last isoprene unit. The “plastoquinone D” preparation gave a similar result. 5. Radioactivity from [2‐14C]mevalonic acid was incorporated into phylloquinone, plastoquinone, “plastoquinone C”, α‐tocopherol, α‐tocopherolquinone, ubiquinone‐10, β‐carotene, 3β‐hydroxysterols and solanesol. The incorporation of 14C activity into the latter component (0.2%) was lower than that reported by a previous worker (15%). Ozonolytic degradation of plastoquinone established that all the 14C radioactivity was in the nonaprenyl side chain. 6. From a comparison of the relative incorporation of 14C from 14CO2 and [2‐14C]‐mevalonic acid into the various terpenoids examined evidence was obtained to support the proposals that solanesol and the prenyl side chains of phylloquinone, plastoquinone, “plastoquinone C”, α‐tocopherol and α‐tocopherolquinone are biosynthesized in the chloroplast, the phytosterols being synthesized elsewhere. Copyright © 1968, Wiley Blackwell. All rights reserved