Fourier-transform infrared and Raman spectroscopic evidence for the incorporation of cinnamaldehydes into the lignin of transgenic tobacco (Nicotiana tabacum L.) plants with reduced expression of cinnamyl alcohol dehydrogenase |
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Authors: | Derek Stewart Nabila Yahiaoui Gordon J McDougall Kate Myton Christiané Marque Alain M Boudet James Haigh |
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Institution: | (1) Unit for Industrial Crops, Department of Cellular and Environmental Physiology, Scottish Crop Research Institute, Dundee, DD2 5DA, UK, GB;(2) Unité Mixte de Recherche UPS-CNRS No 5546, University Paul Sabatier, 118 Route de Narbonne, 31602 Toulouse Cedex, France, FR;(3) Department of Chemistry, University of Southampton, Southampton, SO17 1BJ, UK, GB |
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Abstract: | Xylem from stems of genetically manipulated tobacco plants which had had cinnamyl alcohol dehydrogenase (CAD; EC 1.1.1.195)
activity down-regulated to a greater or lesser degree (clones 37 and 49, respectively) by the insertion of antisense CAD cDNA
had similar, or slightly higher, lignin contents than xylem from wild-type plants. Fourier-transform infrared (FT-IR) microspectroscopy
indicated that down-regulation of CAD had resulted in the incorporation of moieties with conjugated carbonyl groups into lignin
and that the overall extent of cross-linking, particularly of guaiacyl (4-hydroxy-3-methoxyphenyl) rings, in the lignin had
altered. The FT-Raman spectra of manipulated xylem exhibited maxima consistent with the presence of elevated levels of aldehydic
groups conjugated to a carbon-carbon double bond and a guaiacyl ring. These maxima were particularly intense in the spectra
of xylem from clone 37, the xylem of which exhibits a uniform red coloration, and their absolute frequencies matched those
of coniferaldehyde. Furthermore, xylem from clone 37 was found to have a higher content of carbonyl groups than that of clone
49 or the wild-type (clone 37: clone 49: wild-type; 2.4:1.6:1.0) as measured by a degradative chemical method. This is the
first report of the combined use of FT-IR and FT-Raman spectroscopies to study lignin structure in situ. These analyses provide
strong evidence for the incorporation of cinnamaldehyde groups into the lignin of transgenic plants with down-regulated CAD
expression. In addition, these non-destructive analyses also suggest that the plants transformed with antisense CAD, in particular
clone 37, may contain lignin that is less condensed (cross-linked) than that of the wild-type.
Received: 27 May 1996 / Accepted: 30 July 1996 |
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Keywords: | Key words: Lignin-Cell walls Cinnamyl alcohol dehydrogenase Infrared Raman |
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