Submitted to: Meeting Abstract
Publication Type: Book / chapter
Publication Acceptance Date: 9/9/2002
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: Lignin makes up approximately 20% of poplar wood and needs to be degraded and extracted during chemical pulping, a process that is both expensive and environmentally unfriendly. Over the past years, we have generated transgenic poplars, downregulated for cinnamyl alcohol dehydrogenase (CAD), caffeic acid-O-methyltransferase (COMT) and caffeoyl-CoA-O-methyltransferase (CCoAOMT), three enzymes playing important roles in monolignol biosynthesis. These plants have been analysed for their lignin characteristics. The transgenic poplars downregulated for CAD and COMT have additionally been grown in field trials and wood of these trees has been evaluated for Kraft pulping. The results show that it is possible to modify lignin amount and composition and to improve lignin extractability; lignin is more easily extracted from wood of the CAD-downregulated trees, whereas that of the COMT-downregulated trees is less suitable for Kraft pulping. Detailed NMR analysis of lignin from COMT-downregulated poplars reveals the presence of benzodioxane structures, which are derived from coupling of 5-hydroxyconiferyl alcohol with the lignin polymer. These data have shown that monolignols other than p-coumaryl, coniferyl and sinapyl alcohol can be incorporated into lignin. Analysis of poplar downregulated for CCoAOMT shows that CCoAOMT is involved in the synthesis of both syringyl and guaiacyl units, and argue that sinapic is not an important precursor for syringyl lignin synthesis in vivo in poplar.