Abstract
The structure and composition of the β-diketones in barley spike and carnation leaf epicuticular waxes have been determined by gas liquid chromatography-mass spectrometry. Barley wax contained, in addition to the well known hentriacontan-14,16-dione, small amounts of tritriacontan-16,18-dione, nonacosan-12,14-dione and nonacosan-14,16-dione. Five β-diketones were identified in carnation wax: nonacosan-10,12-dione, nonacosan-12,14-dione, hentriacontan-12,14-dione, tritriacontan-12,14-dione and tritriacontan-14,16-dione. The biosynthesis of the β-diketones was studied by incorporating various precursors into tissue slices of barley spikes with awns removed. Incorporation of [1-14C]-pentadecanoic acid labelled a novel C30 β-diketone which upon cleavage contained the14C in the C16–30 end. This confirms that the carbon chain of the C31 β-diketone is formed in vivo by an elongation mechanism which proceeds from the C31 toward the C1 end of the molecule. A comparison of the position of label within the β-diketone chains synthesized from C12, C14, C16 and C18 labelled precursors revealed that the β-keto acyl elongase which is responsible for β-diketone carbon chain synthesis has the following specificities; C14 or C16 chains serve equally well as primers; C12 chains are first elongated to C14 or C16 before they can serve as primers; C18 chains can not serve as primers. After protection of the β-diketo groups by the β-keto acyl elongase either 7 or 8 additional C2 units are added before the presumed decarboxylation to yield the complete β-diketone molecule.
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Abbreviations
- GLC:
-
gas liquid chromatography
- HEA:
-
hexane:diethyl ether:acetic acid
- MS:
-
mass spectrometry
- TLC:
-
thin layer chromatography
- TMSi:
-
trimethylsilyl
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Mikkelsen, J.D. Structure and biosynthesis of β-diketones in barley spike epicuticular wax. Carlsberg Res. Commun. 44, 133–147 (1979). https://doi.org/10.1007/BF02906294
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DOI: https://doi.org/10.1007/BF02906294