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Study shows what makes plant cell walls compress and stretch

Three sealed containers containing gel in which hemicelluloses have been isolated for observation.
Researchers added pure mannans and xylans separately to cellulose media in order to observe how they became integrated in the fibrillar network of plants.
Published Sep 17, 2020

Researchers have identified the individual mechanical functions of wood hemicelluloses in plant cell walls for the first time.

New findings about the building blocks of plant fibres open the door to advances in material engineering as well as food and agriculture, a Swedish-Australian research collaboration reported. The findings, published today in Nature Communications , identify the individual mechanical functions of wood hemicelluloses in plant cell walls for the first time.

A cooperation between researchers from KTH Royal Institute of Technology, the University of Nottingham, and The University of Queensland, the study shows how two hemicelluloses, xylans and mannans, contribute different qualities as they bind together with cellulose to provide plant fibre integrity.

An SEM image showing the fibrillar network of a spruce cell wall.
One of the cellulose networks the researchers studied. The network has incorporated isolated mannans and xylans from spruce wood.

Wood is composed of three basic components: lignin, cellulose and hemicellulose, and the molecular structure of wood depends on whether the main hemicellulose is xylan or mannan, KTH researcher Francisco Vilaplana  says. In conifers, like spruce, the primary hemicellulose is mannan. While in flowering plants, like birch, it’s xylan.

“What we have found is that xylans and mannans appear to influence differently the biomechanical contributions to cellulose fibrillar networks,” Vilaplana says. “Mannans improve the compression, or pulling together of cellulose networks, while xylans improve their extension, or pulling them apart.”

Compression and extension are both important in order for plant cells walls to fulfill their role in the structure of wood, Vilaplana says. But with the knowledge of each hemicellulose’s role, there are new possibilities for developing better, environmentally-sustainable plant-based materials.

Researcher Jennie Berglund is pulling cellulose gel from container in a laboratory.
Researcher Jennie Berglund conducted the observations of hemicelluloses, using a cellulose model gel..

“You could potentially use distinct hemicelluloses to tune properties of biodegradable celluloses, in order to replace everyday petroleum-based products such as plastic film for food storage, where you want stretchability, or foams where you want compressibility,” Vilaplana says.

In agriculture, these findings can also be used, for example, in selecting crop varieties with desirable mechanical properties in the field or preferred textural properties when used in foods.

Parsing xylans’ and mannans’ mechanical effects hasn’t been easy, since no wood exists without both hemicellulose components. So the researchers used a method in which a bacterium called Komagataeibacter xylinus synthesizes and secretes pure cellulose. Into the media where this cellulose is secreted, the researchers added pure mannans and xylans separately to observe how they became integrated in the fibrillar network, in much the same way as they would when cell walls, or wood, are produced.

Jennie Berglund, a former PhD student at KTH, performed a research secondment in Brisbane (Australia) where she learned how to use the bacterium to produce these plant cell wall analogues. “I learned so much during my time in Australia and it was also a fantastic experience on a personal level of course” she says.

Collaborating on the research were Wallenberg Wood Science Centre at KTH and The Centre for Nutrition and Food Sciences in the Queensland Alliance for Agriculture and Food Innovation at the University of Queensland.

The research was funded by the Knut and Alice Wallenberg Foundation through the Wallenberg Wood Science Centre and the Australian Research Council Centre of Excellence in Plant Cell Walls.

David Callahan

Wood hemicelluloses exert distinct biomechanical contributions to cellulose fibrillar networks, Nature Communications

DOI: 10.1038/s41467-020-18390-z