title: Ultrastructure and mechanical properties of populus wood with reduced lignin content caused by transgenic down-regulation of cinnamate 4-hydroxylase.
abstract: Several key enzymes in lignin biosynthesis of Populus have been down-regulated by transgenic 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.
authors.affiliation: Department of Fiber and Polymer Technology, Division of Biocomposites, Royal Institute of Technology (KTH), SE-100 44 Stockholm, Sweden.
authors.forename: Ingela
authors.initials: I
authors.lastname: Bjurhager
authors.forename: Anne-Mari
authors.initials: AM
authors.lastname: Olsson
authors.forename: Bo
authors.initials: B
authors.lastname: Zhang
authors.forename: Lorenz
authors.initials: L
authors.lastname: Gerber
authors.forename: Manoj
authors.initials: M
authors.lastname: Kumar
authors.forename: Lars A
authors.initials: LA
authors.lastname: Berglund
authors.forename: Ingo
authors.initials: I
authors.lastname: Burgert
authors.forename: Björn
authors.initials: B
authors.lastname: Sundberg
authors.forename: Lennart
authors.initials: L
authors.lastname: Salmén
mesh_terms: D015536:Down-Regulation; D008401:Gas Chromatography-Mass Spectrometry; D008031:Lignin / Q000378:metabolism*; D018625:Microscopy, Atomic Force; D030821:Plants, Genetically Modified / Q000201:enzymology* / Q000235:genetics*; D011134:Polysaccharides / Q000378:metabolism; D032107:Populus / Q000201:enzymology* / Q000235:genetics / Q000648:ultrastructure; D012333:RNA, Messenger / Q000235:genetics; D018749:RNA, Plant / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017550:Spectroscopy, Fourier Transform Infrared; D013696:Temperature; D013718:Tensile Strength; D050564:Trans-Cinnamate 4-Monooxygenase / Q000032:analysis / Q000037:antagonists & inhibitors / Q000235:genetics*; D014867:Water / Q000737:chemistry; D014934:Wood / Q000737:chemistry* / Q000235:genetics / Q000648:ultrastructure
chemical_list: D011134:Polysaccharides; D012333:RNA, Messenger; D018749:RNA, Plant; D014867:Water; C007916:hemicellulose; D008031:Lignin; D050564:Trans-Cinnamate 4-Monooxygenase