Nanostructure of living wood exposed
Image: Wood nanostructure.
UK-based researchers have captured the visible nanostructure of living wood for the first time using an advanced low-temperature scanning electron microscope.
Cryo-SEM allowed Dr Jan Lyczakowski, originally from Cambridge University and now at Jagiellonian University, Poland, and colleagues to see the composition of cylindrical structures called macrofibrils.
The researchers could also observe how the molecular arrangement of these structures differs between plants, shedding new light on how this might impact on wood density and strength
“It is the molecular architecture of wood that determines its strength, but until now we didn’t know the precise molecular arrangement of macrofibrils in the wood cells,” says Lyczakowski.
Lyczakowski and colleagues adapted cryo-SEM to image the nanoscale architecture of tree cell walls in their living state, capturing microscopic detail of the secondary cell wall macrofibrils.
To compare different trees, the researchers collected wood samples from spruce, gingko and poplar trees in the Cambridge University Botanic Garden.
Samples were snap-frozen down to minus 200°C to preserve the cells in the live hydrated state, then coated in an ultra-thin platinum film three nanometres thick to give good visible contrast under the microscope.
“Our cryo-SEM is a significant advance over previously used techniques and has allowed us to image hydrated wood cells for the first time,” highlights Dr Raymond Wightman, Microscopy Core Facility Manager at Sainsbury Laboratory Cambridge University (SCLU).
“It has revealed that there are macrofibril structures with a diameter exceeding 10 nanometres in both softwood and hardwood species, and confirmed they are common across all trees studied,” he adds.
The researchers also imaged the secondary cell walls of Arabidopsis thaliana, an annual plant widely used as the standard reference plant for genetics and molecular biology research.
They found that it too had prominent macrofibril structures.
Using a collection of Arabidopsis plants with different mutations relating to their secondary cell wall formation, the researchers was able to study the involvement of specific molecules in the formation and maturation of macrofibrils.
As Dr Matthieu Bourdon, a research associate at SLCU, says: “The variants of Arabidopsis allowed us to determine the contribution of different molecules - like cellulose, xylan and lignin - to macrofibril formation and maturation. As a result, we are now developing a better understanding of the processes involved in assembling cell walls.”
“Visualising the molecular architecture of wood allows us to investigate how changing the arrangement of certain polymers within it might alter its strength,” points out Professor Paul Dupree from Cambridge’s Department of Biochemistry. “Understanding how the components of wood come together to make super strong structures is important for understanding both how plants mature, and for new materials design.”
“There is increasing interest around the world in using timber as a lighter and greener construction material,” he adds. “If we can increase the strength of wood, we may start seeing more major constructions moving away from steel and concrete to timber.”
Research is published in Frontiers in Plant Science.