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Ultrastructure and Mechanical Properties of Populus Wood with Reduced Lignin Content Caused by Transgenic Down-Regulation of Cinnamate 4-Hydroxylase
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Biocomposites.
Department of Biomaterials, Max Planck Institute of Colloids and Interfaces.
Umeå Plant Science Center, Swedish University of Agricultural Sciences (SLU).
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2010 (English)In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 11, no 9, 2359-2365 p.Article in journal (Refereed) Published
Abstract [en]

Several key enzymes in lignin biosynthesis of Populus have been down-regulated by transgenie approaches to investigate their role in wood lignification and to explore their potential for lignin modification. Cinnamate 4-hydroxylase is an enzyme in the early phenylpropanoid pathway that has not yet been functionally analyzed in Populus. This study shows that down-regulation of cinnamate 4-hydroxylase reduced Klason lignin content by 30% with no significant change in syringyl to guaiacyl ratio. The lignin reduction resulted in ultrastructural differences of the wood and a 10% decrease in wood density. Mechanical properties investigated by tensile tests and dynamic mechanical analysis showed a decrease in stiffness, which could be explained by the lower density. The study demonstrates that a large modification in lignin content only has minor influences on tensile properties of wood in its axial direction and highlights the usefulness of wood modified beyond its natural variation by transgene technology in exploring the impact of wood biopolymer composition and ultrastructure on its material properties.

Place, publisher, year, edition, pages
2010. Vol. 11, no 9, 2359-2365 p.
Keyword [en]
Axial direction, Cinnamate 4-hydroxylase, Down-regulation, Guaiacyl, Key enzymes, Klason lignin, Lignin biosynthesis, Lignin contents, Lignin modifications, Lower density, Material property, Natural variation, Phenylpropanoid pathways, Populus, Tensile tests, Transgene, Transgenic approaches, Transgenics, Wood density, Biochemistry, Density (specific gravity), Dynamic analysis, Dynamic mechanical analysis, Enzymes, Lignin, Plants (botany), Stiffness, Tensile testing, Wood
National Category
Chemical Sciences
URN: urn:nbn:se:kth:diva-26700DOI: 10.1021/bm100487eISI: 000281629600023ScopusID: 2-s2.0-77956536493OAI: diva2:372928
QC 20101129Available from: 2010-11-29 Created: 2010-11-26 Last updated: 2011-04-20Bibliographically approved
In thesis
1. Effects of Cell Wall Structure on Tensile Properties of Hardwood: Effect of down-regulation of lignin on mechanical performance of transgenic hybrid aspen. Effect of chemical degradation on mechanical performance of archaeological oak from the Vasa ship.
Open this publication in new window or tab >>Effects of Cell Wall Structure on Tensile Properties of Hardwood: Effect of down-regulation of lignin on mechanical performance of transgenic hybrid aspen. Effect of chemical degradation on mechanical performance of archaeological oak from the Vasa ship.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Wood is a complex material and the mechanical properties are influencedby a number of structural parameters. The objective of this study has been toinvestigate the relationship between the structure and the mechanical propertiesof hardwood. Two levels were of special interest, viz. the cellular structureand morphology of the wood, and the ultra-structure of the cell wall. In thenext step, it was of interest to examine how the mechanical properties ofhardwood change with spontaneous/induced changes in morphology and/orchemical composition beyond the natural variation found in nature.

Together, this constituted the framework and basis for two larger projects,one on European aspen (Populus tremula) and hybrid aspen (Populus tremulax Populus tremuloides), and one on European oak (Quercus robur). Amethodology was developed where the concept of relative density and compositemechanics rules served as two useful tools to assess the properties ofthe cell wall. Tensile testing in the longitudinal direction was combined withchemical examination of the material. This approach made it possible to revealthe mechanical role of the lignin in the cell wall of transgenic aspen trees,and investigate the consequences of holocellulose degradation in archaeologicaloak from the Vasa ship.

The study on transgenic aspen showed that a major reduction in lignin inPopulus leads to a small but significant reduction in the longitudinal stiffness.The longitudinal tensile strength was not reduced. The results are explainableby the fact that the load-bearing cellulose in the transgenic aspen retained itscrystallinity, aggregate size, microfibril angle, and absolute content per unitvolume. The results can contribute to the ongoing task of investigating andpinpointing the precise function of lignin in the cell wall of trees.

The mechanical property study on Vasa oak showed that the longitudinaltensile strength is severely reduced in several regions of the ship, andthat the reduction correlates with reduced average molecular weight of theholocellulose. This could not have been foreseen without a thorough mechanicaland chemical investigation, since the Vasa wood (with exception fromthe bacterially degraded surface regions) is morphologically intact and witha micro-structure comparable to that of recent oak. The results can be usedin the ongoing task of mapping the condition of the Vasa wood.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. viii, 67 p.
Trita-CHE-Report, ISSN 1654-1081 ; 2011:14
tensile strength, transgenic hybrid aspen, lignin down-regulation, the Vasa ship, chemical degradation, longitudinell draghållfasthet, transgen hybridasp, ligninnedreglering, Vasaskeppet, kemisk nedbrytning
National Category
Engineering and Technology
urn:nbn:se:kth:diva-32190 (URN)978-91-7415-914-1 (ISBN)
Public defence
2011-04-29, F3, Lindstedtsvägen 26, Stockholm, 13:00 (English)
QC 20110420Available from: 2011-04-20 Created: 2011-04-08 Last updated: 2011-04-26Bibliographically approved

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