Periodic Reporting for period 1 - XYLAN-2.0 (Plant biomass for high-performing sustainable materials)
Período documentado: 2019-04-08 hasta 2021-04-07
Wood represents an abundant and increasingly important natural resource. It mainly consists of a number of cell types that have undergone what is called "secondary cell wall formation”. This is a process where the normal cell wall is thickened extensively after the cell has reached its full size and shape. This strengthens the cell wall tremendously and the cell types that do this, such as fiber cells, often serve a function of structural support to the tissue where they are found, such as in the stem of trees. The mechanical properties of wood are therefore closely linked to secondary cell wall formation process. However, a lot of unresolved questions remain in this area, for instance what rules governs the wall components to self-organize into the observed patterns during wall assembly outside the cell and how do the plant exert control over these self-organizing processes? If elucidated, the knowledge could lead to improved uses of wood-based products, particularly high-performance materials. This could contribute significantly to reduce the use of plastic and strengthen a carbon-neutral economy. The overall objectives are to link changes in the basic building blocks of secondary cell wall formation and correlate these to changes in self-organization of these components. The complexity of the components makes this challenging and experiments need to be done both in living plant systems and in the test-tube for then to compare the results between these two major types of experimental systems. It is a major goal to be able to control the process in the test-tube in a similar manner as the plants are doing it, as this argues that we have gained a good understanding of the biological phenomena. The knowledge can then be applied in making better wood-based materials.
I have successfully linked changes in one of the building blocks of secondary cell walls, namely glucuronoxylan, with changes in cellulose fibril alignment and network architecture, which at least partially arise through self-organization. The work shows that glucuronoxylan is very powerful in affecting the cellulose organization as small changes in the polysaccharide structure of glucuronoxylan leads to major changes in cellulose organization. It suggests that the plant deploys glucuronoxylan as part of a strategy to control cellulose fibril self-organization into complex but deliberate network patterns. I have successfully developed a medium-throughput strategy based on scanning electron microscopy to look at more glucuronoxylan mutants with altered structure. I am deploying this towards getting a more complete picture of how the different structural aspects of glucuronoxylan play different roles in modulating cellulose self-assembly. Complementary to the work in plants, I have developed a test-tube method to measure cellulose self-assembly in the presence of glucuronoxylan. Using this method, I find that the presence of glucuronoxylan leads to a higher degree of cellulose defibrillation, increased transparency and swelling of cellulose gels, and reduced storage and loss modulus in rheology assays. This have led me to propose that xylan help reduce cellulose inter-fibril friction, which is an interesting new perspective highly relevant for the microcopy work that I have done in plants with altered glucuronoxylan. Finally, I have tested one candidate alga for the potential to produce recombinant xylan and have identified a second candidate to explore next, as the results from the first candidate were not promising. I have presented my work with oral presentations at two international conferences and published one research article, while three additional research articles are in the pipeline.
The fundamental questions that I am asking with this work have been investigated in the field for more than 30 years. The resent development of mutant collections that are thoroughly characterized along with much improved microscopy methods for the nm-scale and new methods in cellulose defibrillation, however, have paved the way for asking old questions in new ways. My work is therefore very original, being one of the first studies to investigate the effect on cellulose network organization in non-cellulose mutants, i.e. xylan mutants. I have shown that the effect is surprisingly strong, suggesting that this is a rich area of future investigations, and I have shown that this can be done in a medium-throughput manner. The same applies to the work with the test-tube method involving cellulose defibrillation in the presence of glucuronoxylan. This work is the first of its kind and therefore very innovative. It is my hope that my work with inspire other researchers in the field to take up these methods and re-invigorate this area of research. Indeed, I believe that this area is ripe for many new discoveries and will be a major focus area in the field in a number of years. Surely, with time, this will have wider socio-economic impact through the development of better performing and sustainably produced materials made from plant biomass. If we understand how Nature does it, we can take those same principles and apply them to our own interest. When it comes to biomass-based products, such as wood and paper, we still have a lot learn from Nature, which is far ahead in producing materials with truly high-performance physical properties. Plant biomass is the most abundant resource on Earth for producing products that today are made from for instance plastic. Conversion to a renewable and carbon-neutral economy by substituting fossil fuel-based products with plant biomass-based products is of the essence in these dire times with impending climate change and so will continue to be for the decades to come.