Developmental and Structural Section
Koehler, Lothar , Ewers, Frank W. , Telewski, Frank W. .
Lignin Composition, Mechanical Properties, Conductivity and Response to Wind of F5H Transgenic Poplars.
WHILE the influence of overall lignin content on mechanical properties has been well investigated, little is known about the mechanical consequences of altered lignin monomer composition. Using transgenic poplar trees expressing different degrees of increased syringyl to guaiacyl ratio we investigate the effects of lignin composition on biomechanics, plant allometry, conductivity, and the response of trees to wind. The altered lignin monomer composition is achieved by over-expression of the gene F5H encoding ferulate 5-hydroxylase.
Increasing syringyl content leads to correspondingly higher mechanical stiffness and a subsequent change in allometry to a relatively more slender and taller stem. This illustrates advantages due to the evolution of syringyl lignin concomitant with fiber cells in angiosperms and suggests feed-back between wood mechanical properties and growth allocation causing the tree to invest less material for stem diameter when the same flexural stiffness is reached at a smaller stem diameter due to an increased elastic modulus.
Microspectrophotometric analysis of lignin composition of controls and trees grown under influence of simulated wind reveals: (1) The typical pattern of differences in lignin monomer composition between different cell types is conserved in the mutant, showing higher relative guaiacyl content in vessel walls and higher syringyl content in fibers. Considering the bearing of syringyl content on the elastic modulus shown by our study, the conserved pattern of lignin composition according to cell type could be a hint to the importance of a gradient in the mechanical properties between vessel and fiber walls. This will be discussed with regard to resistance to embolism of the vessels. (2) The tree actively modifies lignin monomer composition to adjust the mechanical properties of its wood to windy environment. The reaction of the transgenics to simulated wind in terms of changes in mechanical properties and syringyl content is comparable to the wild-type.
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1 - Michigan State University, Department of Plant Biology, 166 Plant Biology Building, East Lansing, Michigan, 48824-1312, USA
Presentation Type: Oral Paper:Papers for Sections
Location: 303/Bell Memorial Union
Date: Wednesday, August 2nd, 2006
Time: 8:15 AM