Wood fibre cell wall structure

Objectif

A.BACKGROUND

The wood fibre cell wall consists mainly of cellulose, hemicellulose and lignin. A cellulose chain consists of about 10 000 glucose units, 30-40 parallel cellulose chains associated to form microfibrils which have crystalline and amorphous parts. The hemicelluloses contain pentose sugars and hexoses, have a lower degree of polymerisation than cellulose and are water soluble. Lignin consists of phenyl propane units coupled together and also contains methoxyl and hydroxyl groups. It is highly branched, not crystalline, water insoluble and is probably bonded to hemicellulose.

Wood fibres have a complex ultrastructure and are composed of several layers (cell walls). These cell wall layers contain different amounts of cellulose, hemicellulose and lignin. From the cell lumen outwards, the layers are the secondary wall (S), the primary wall (P) and the middle lamella (ML) between cells. The ML has a high percentage of lignin which is decreasing towards the cell lumen. The P has a mixture of cellulose, hemicellulose and lignin. The S has three layers and is built up by lamellae formed by the cellulose microfibrils intermixed with some hemicellulose and lignin.

The chemistry and ultrastructure of this complicated network of wood components determines the properties of the resulting lignocellulosic fibre of both annual and perennial plants. This is a result of the biosynthetic and biochemical processes during cell wall formation. The final fibre properties are of great importance for the quality of pulp and paper as well as timber and sawn products. Our knowledge of changes in fibre walls and their chemical components during pulp and paper making processes is, however, incomplete and needs to be improved. New ideas on how (chemical) modifications can be made at the ultrastructural level (scale from 1 nm to about 500 nm resolution of the fibre) are required to develop new cellulose and wood-based products and composite materials, improve production processes and thus optimally utilise the industrial potential of wood fibres.

In trees and other woody plants, the biosynthesis of lignin has been modified by changes in the enzymatic machinery. The structure of lignin in certain trees has been altered and weakened, thereby producing fibres that are easier to pulp and require less chemical and energy inputs. In contrast, lignin could be strengthened making it more difficult to remove, which may, in turn, produce stronger timber and solid wood products, or produce woody plants that are more resistant to wind/rain/decay/pathogens. This type of research is important for general knowledge on wood structure and ultrastructure.

Biosynthesis and assembly of secondary wall components like hemicellulose(s) in trees and fibre-yielding plants is also important for fibre properties. Here the enzymes involved are under investigation. An expressed sequence tag (EST) library of developing wood of hybrid aspen is being established which will provide markers for wood formation and will be a source of new genes and new enzymes important for cell wall formation. This research may in the future facilitate growth of superior trees for pulping and timber production. As a complement to EST work, changes in proteins expressed during xylem formation may be studied.

The formation and ultrastructure of cellulose microfibrils and fibres are under investigation in several laboratories. The aim of these studies is to determine what effect hemicellulose and cellulose structures have on the properties of wood fibres and other fibres not only during pulping or solid wood production, but also for upgrading and end-use of different fibres. Non-wood fibres which are studied include straw, kenaf, flax, hemp, sisal, jute, and oil palm.

Selective removal (peeling) of cellulose, hemicelluloses or lignin from lignocellulose fibres with specific enzymes may be used for studying fibre structure at all levels of resolution. Cellulases, hemicellulases and ligninases are important in this respect and may reveal new details of fibre morphology and ultrastructure.

Despite the knowledge from earlier and ongoing research, we still lack information on the true structure of wood fibres. Rapid developments in molecular biology, microscopy and spectroscopy has now brought about techniques, which will make it possible to study more closely the basic building elements of plant fibres and how they are influenced by chemical, enzymatic and mechanical treatments.

Research in the field of wood fibre ultrastructure is very complex and requires input from diverse fields of sciences such as molecular biology, plant physiology, biochemistry, wood and fibre chemistry, wood technology, microbiology, microscopy etc. Since a great number of researchers from different fields will be brought together in this Action, new discoveries of wood fibre ultrastructure and its formation will result in novel and optimised use of the lignocellulosic fibres.

B.OBJECTIVES AND BENEFITS

The main objective of the Action is to provide academia, applied researchers, forest breeders and wood processing industries with an improved understanding of the chemistry and ultrastructure of wood fibre cell walls. This increased knowledge is essential for development of new methods of industrial fibre modification and production of improved fibres.

The means to achieve this objective would be:

-To have a better understanding and be able to control the assembly of fibre walls.

-To find better methods and tools for characterisation of wood fibre cell walls, their native structure and how this structure can be changed after chemical, mechanical and enzymatic treatments.

-This will be obtained by bringing together scientists from a broad range of ultrastructural research on different types of cell walls to exchange their knowledge in a synergistic way.

The benefits from this Action will be:

-An increased knowledge on how fibre properties at the molecular and ultrastructural level relate to the properties of pulp, paper, solid wood products and other types of wood-based products.

-The knowledge may result in improvements in the existing products and new types of products for the consumer market.

-Improved models for cellulose, hemicellulose, lignin and the whole wood fibre cell wall will be built.

-The Action will help Europe to maintain a position at the forefront of knowledge in this field and thereby retain the competitiveness of European forest industries.

-The Action will improve the co-operation between ultrastructural research groups in Europe and increase the exchange of methodologies, ideas, graduate students and researchers between these groups.

C.SCIENTIFIC PROGRAMME

To achieve the objective, the Action will bring together scientists from a broad range of research areas to exchange knowledge, share experiences in methodology and to encourage multi- and interdisciplinary co-operation to solve ultrastructural research problems. In addition to bringing together expertise through symposia, workshops etc., the action will also stimulate the exchange of researchers and research students among participating partners.

The Action serves as an important complement to two other COST Actions namely E10 (Wood properties for industrial use) and E11(Characterisation methods for fibres and paper). Action E10 is directed towards the macroscopic level of fibre characterisation which means that the cross-sectorial action proposed here is a very suitable complement. In the developement of the work programme for action E11, the area of wood fibre ultrastructure has deliberately been omitted assuming that a new COST Action would be established in this field.

It is proposed that the Action is divided in three Scientific Areas:

Area 1:Biosynthesis of wood fibre cell wall components

Area 2:Methods for characterisation of cell wall components and ultrastructure

Area 3:Models for wood cell walls including cellulose, hemicellulose and lignin

The division into Scientific areas, as seen in the detailed scientific programme, should be discussed further, depending on the specific interests of the final participants. Area 1, biosynthesis of wood components, includes components from wood and from all kinds of lignocellulosics. Area 2 will also include other types of cell walls in order to benefit from experiences gained from research on non-woody cell walls. Area 3, Models for wood cell walls including cellulose, hemicellulose and lignin, can be seen as a result (benefit) of the other two areas.

Scientific programme Area 1 (Biosynthesis)

The research will focus on the formation and deposition of the three main wood components cellulose, hemicellulose and lignin, and the genes and enzymes involved in these processes. Possibilities of creating wood and non-wood plants with superior properties are considered. Lignocellulosic fibres from hybrid aspen, poplar, spruce, pine (maritime and Scot's), birch and non-wood plants will be studied. Specific labelling of lignin with 13C during lignin formation will be used for solid state NMR studies.

Scientific programme Area 2 (Characterisation)

The research will focus on ultrastructural and chemical characterisation of cellulose, hemicellulose and lignin and localisation of these wood components in fibre cell walls. As an aid selective removal of the respective wood components using cellulases, hemicellulases (mannanase, xylanase) and ligninases (laccase, lignin peroxidase, Mn-peroxidase) will be used. Influence on ultrastructure of mechanical and chemical treatments are also studied. The above studies are related to formation and characterisation of dislocations, nodes and kinks in fibres. Characterisation and location of lignin will be studied using 13C-NMR and 14C/3H-labelled pulp lignin plus microautoradiography. Properties of lignin-hemicellulose complexes will be studied in for example wheat straw. Biodegradation of lignocellulosic materials by micro-organisms and their enzymes plus electron microscopy will help to elucidate ultrastructural changes during degradation.

Scientific programme Area 3 (Modelling)

Modelling studies will concentrate on the elucidation of an ultrastructural model of a Norwegian spruce fibre using newly gathered information plus information from old models. Much information is expected to come from related research in order to build this model. Structural modelling of cellulose using atomic force microscopy and other techniques will be conducted, as well as detailed studies on the interaction between cellulose, hemicellulose and lignin in fibres during pulping.

Short points in the scientific programme of Area 1

-Developmental and biochemical regulation of cell wall formation and lignin deposition,

-Possibilities to affect wood formation and fibre properties in transgenic plants,

-Studies on lignin biosynthesis (amount and type of lignin),

-Studies on cell wall-forming enzymes.

Short points in the scientific programme of Area 2

-Characterise the surface ultrastructure of fibres,

-Study influence of enzymatic, mechanical and chemical treatments on (ultra)structure,

-Study fibre dislocations, nodes and kinks (background and importance in paper strength),

-Fibre chemistry: elucidate structure of lignin, cellulose and hemicelluloses,

-Role of surface components in fibre cell to cell adhesion/separation,

-Fibre surface morphology: location of lignin, cellulose and hemicelluloses,

-13C and 14C/3H-labelled phenols as markers for pulp and fibre lignin,

-Selective removal of cell wall components using enzymes (hemi/cellulases and ligninases),

-Structural aspects of lignin-hemicellulose complex in the cell wall,

-Development of cellulosic composite materials,

-Biodegradation of lignocellulosic materials and studies on cell wall degrading enzymes.

Short points in the scientific programme of Area 3

-Generate ultrastructural models of fibres and tracheid cell walls, e.g. Norway spruce,

-Generate cellulose models using AFM and other techniques,

-Build models for hemicellulose and lignin in combination with overall cell wall structure.

Instruments and biochemical/analytical tools to be used in the COST.

The different techniques given are used more or less in all 3 areas.

-Scanning Electron Microscopy,

-Transmission Electron Microscopy,

-Field Emission Scanning Electron Microscopy,

-Environmental Scanning Electron Microscopy,

-Atomic Force Microscopy,

-Luminescence Spectroscopy,

-Microautoradiography,

-Confocal microscopy,

-Image analyses technique,

-FTIR spectroscopy and microspectroscopic analysis,

-Solid state 13C-NMR, liquid state 2D-NMR,

-Liquid scintillation spectroscopy,

-Specific purified polysaccharide- and lignin-degrading enzymes,

-Monoclonal and/or polyclonal antibodies (immunocytochemistry),

-HPLC, MS, FPLC.

D.ORGANISATION AND TIMETABLE

The Action will be led by a Management committee (MC). Working Groups (WG) are anticipated for the scientific areas:

Working Group 1:Biosynthesis of wood fibre cell wall components

Working Group 2:Methods for characterisation of cell wall components and ultrastructure

Working Group 3:Models for wood cell walls including cellulose, hemicellulose and lignin

- Coordinator 1? Working Group 1

Management Committee MC? Coordinator 2? Working Group 2

- Coordinator 3? Working Group 3

Responsibility for the detailed planning, execution and documentation of each individual activity is delegated by the MC to the three Working Groups (WG), each led by a coordinator appointed by the MC. The coordinator of each WG should preferably be a member of the MC. The duration of the Action is planned to be 4 years. Meetings are planned to be held once a year in the separate working groups and at least once a year in the MC.

In connection with the above meetings, workshops with the 3 Working groups together should take place. At the end of year 4, a final conference will be held and a final report will be prepared for dissemination. This conference will be open for all interested parties.

Programme(s)

IC-COST - European cooperation in the field of scientific and technical research (COST), 1971-

Thème(s)

14 - Forestry

Appel à propositions

Data not available

Régime de financement

Data not available

Coordinateur

N/A

Contribution de l’UE

Aucune donnée

Adresse

Suède

Coût total