© 2007 The Author(s).
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RESEARCH PAPER |
Over-expression of UDP-glucose pyrophosphorylase in hybrid poplar affects carbon allocation
1Department of Wood Science, University of British Columbia, Vancouver, BC, V6T 1Z4 Canada
2National Center for Genetic Resources Preservation, Fort Collins, CO 80521, USA
* To whom correspondence should be addressed: shawnman{at}interchange.ubc.ca
The effects of the over-expression of the Acetobacter xylinum UDP-glucose pyrophosphorylase (UGPase) under the control of the tandem repeat Cauliflower Mosaic Virus promoter (2x35S) on plant metabolism and growth were investigated in hybrid poplar (Populus albaxgrandidentata). Transcript levels, enzyme activity, growth parameters, leaf morphology, structural and soluble carbohydrates, and soluble metabolite levels were quantified in both transgenic and wild-type trees. Transgenic 2x35S::UGPase poplar showed impaired growth rates, displaying reduced height growth and stem diameter. Morphologically, 2x35S::UGPase trees had elongated axial shoots, and leaves that were substantially smaller in size when compared with wild-type trees at equivalent developmental stages. Biochemical analysis revealed significant increases in soluble sugar, starch, and cellulose contents, and concurrent decreases in lignin content. Lignin monomer composition was altered in favour of syringyl moieties. Detailed soluble metabolite analysis revealed that 2x35S::UGPase trees had as much as a 270-fold increase in the salicylic acid 2-O-β-D-glucoside (SAG), a compound typically associated with the stress response. These data suggest that while it is possible to alter the allocation of carbon in favour of cellulose biosynthesis, whole plant changes result in unexpected decreases in growth and an increase in defence metabolites.
Key words: Carbon allocation, cellulose, hybrid poplar, sucrose metabolism, UDP-glucose, UDP-glucose pyrophosphorylase
Received 13 September 2007; Revised 15 October 2007 Accepted 16 October 2007
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