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Electron microscopy of wood

re-Imaging the wall – can we change the micro-structure of timber?

 

Research carried out at the University of Cambridge Sainsbury Laboratory (SLCU) by Dr Matthieu Bourdon and Prof Yrjö Helariutta can help us design biomass more suited for bioenergy and biomaterial applications. The work uses ultra-high magnification microscopy together with genetic engineering of trees to understand and modify plant material.

Plant biomass is predominantly composed of various polysaccharides. In the process of photosynthesis, plants convert carbon dioxide and water into sugars which are then used to synthetize long polysaccharides which give rise to the plant material. Therefore, plant biomass is a natural carbon sink and offers a sustainable energy and biomaterial source for multiple industrial processes. For example, sugars stored in plants, if extracted, can be fermented to bioethanol or biodiesel which are a sustainable alternative to oil based fossil fuels.

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The majority of plant polysaccharides are deposited into successive structural layers and constitute the plant cell walls. Those complex structures surround each plant cell and represent the majority of the plant biomass. Plant cell walls are composed predominantly of cellulose. This rod like crystal structure made from multiple glucose based polysaccharide chains stacked together is more than 30000 times thinner than a human hair. Due to its crystallinity cellulose is highly resistance to mechanical stress and defines the strength of plant material.

“The crystallinity and mechanical stress resistance of cellulose offer many advantages to plants. However, it actually is a nightmare when we want to convert biomass, such as wood, to higher value products.” says Dr Matthieu Bourdon from SLCU. “Paper and Biofuel Industries, as well as nanocellulose manufacturing, need to use vast amounts of energy to break plant cell walls down and make use of the cellulose”. This is believed to be one of the main reasons why the environmental benefit of using plant materials in industrial processes are not obvious.

To understand what governs the resistance of plant material Dr Matthieu Bourdon is using state of the art imaging and microscopy facilities available at the SLCU. “Imaging of cell wall and cellulose microstructure can help us identify features which can be targeted with genetic engineering approaches” says Dr Bourdon. Low temperature Scanning Electron Microscope (cryoSEM) is one of the pieces of equipment used extensively by Dr Bourdon in his research. The instrument uses electron beams to visualise structures with a diameter as small as 10 nano-meters – features 100 000 times smaller than a head of a pin.

 

cryoSEM

CryoSEM image of Arabidopsis xylem vessels (woody tissues of the plant) and its associated close-up. Note the cellulose macro-fibrils ends on the right panel (arrows). Scale bars: 2µm

 

To apply their insights to improvement of biomass properties Dr Bourdon and Prof Helariutta are using Arabidopsis and poplar as  model organisms. “Genetic engineering of trees can help us generate insights relevant to the needs of our industrial partners” points out Dr Bourdon. Currently, the researchers are focusing on disrupting the crystallinity of cellulose present in the wood. “By genetic enrichment of wood with polysaccharides which can infiltrate and brake the cellulose crystals we hope to generate material more suited for processing to paper and fuels”. 

 

WT_vs_GM_poplar

Wild type (left) and GM (right) poplar trees. Trees grow to the same height indicating that the genetic modification introduced has no negative impact on plant development.

 

The work carried out by Dr Matthieu Bourdon and Prof Yrjö Helariutta may help generate a new type of timber derived biomaterials. The project is funded by the European Research Council and supported by the Gatsby Foundation. To learn more about the work described in this article please . To learn more about imaging facilities available at the SLCU please click here.