Biology Reference
In-Depth Information
IV. Synthesis, Conclusion and Prospects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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A. Lessons from the Past Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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B. Some Hints for the Future . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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C. Need for Ambitious Plans for Experimental Field Trials to Identify
Efficient Innovative Biotech Trees . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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ABSTRACT
For the last 20 years, as a complement to biochemical approaches, lignin-modified
transgenic trees have proven to be invaluable tools for deciphering the lignin biosyn-
thetic pathway and increasing our knowledge about the role of lignins in wood-
specific properties important for tree physiology. In addition, their evaluation in the
field has been very useful for the identification of possible routes to improve wood
properties for specific industrial uses, initially pulp and paper making and now biofuel
production. In this chapter, we review our present knowledge gained through numer-
ous studies analysing transgenic trees, with emphasis on field trial evaluations, for
assessing the effects of lignin modification on wood properties and tree physiology.
All the data presented here led to the conclusion that, prior to use in forestry for pulp
and paper or bioenergy production, the fitness of lignin-modified transgenic trees
required careful evaluation in a variety of field environments. Although limited in
number, environmental studies failed to indicate any strong effects of lignin-modified
transgenic trees on the ecosystem. Finally, this review helps to identify some
promising options where biotech trees could be used to further optimize the produc-
tion of wood for human uses.
I. INTRODUCTION: LIGNIN
A MAJOR WOOD POLYMER
Wood is a renewable resource that has always been used by mankind providing
energy, timber and fibres. Beside these traditional uses, wood appears nowadays
as an attractive source of material for biofuel production (
Hinchee et al., 2010
).
For the tree, wood is a complex tissue that fulfils different vital functions
important for its growth and development in a changing environment.
Indeed, xylem vessels and tracheids conduct xylem sap, transporting water
and mineral elements from the roots to the crown, making possible the large
spatial development of trees. In addition, xylem fibres confer to the trunk and
branches the mechanical strength necessary to support over the year the ever-
increasing weight of the tree and to withstand environmental factors such
as wind and snow that may compromise tree equilibrium. To be able to fulfil
these functions, wood exhibits very complex features regarding its structure
and chemical composition, that may be adjusted according to tree develop-
ment and variations in environmental conditions. Wood cell walls are
organized as a multilayer structure resulting from the assembly of different
