Researchers find new complex carbohydrate in barley roots

The discovery of the new polysaccharide in Australia could have 
many applications in food, medicines and industry

At the University of Adelaide in Australia, researchers have discovered a new complex carbohydrate, or polysaccharide, in barley.

They were investigating the gene family that makes up the dietary fibre known as mixed linkage glucan. This is the stuff that makes porridge sticky. But in the process, they saw substantial differences in the sugar content of the plants they were working with. By testing a range of different enzymes and examining results, they found clues that led to the new polysaccharide.

It’s the first of its kind to be discovered in 30 years and, potentially, has many applications in food, medicines and industry.

“The plant cell wall is a complex mixture of different sugars linked together in various configurations with significant differences in composition observed across different plant species,” said Alan Little, senior research scientist.

“Scientists have been teasing apart the components of the cell wall with different analytical techniques for over 150 years now. During the mid-1900s, advances in chemical analysis of the sugars and the linkages they have formed allowed a majority of the cell wall components to be characterized. However, new techniques are allowing the identification of previously hidden structures in various plant species. An example of this is the finding from last year by members of our group of another new polysaccharide in moss. However, the impact of this new finding in barley will be greater as it is found in economically important cereal crops.”

Little said that complex carbohydrates (polysaccharides) consist of sugar molecules (monosaccharides) that are linked together in long complex chains.

This new polysaccharide contains both glucose and xylose. Glucose is one of the most common organic forms of sugar found in nature and is the primary source of energy for many living organisms. Xylose is a natural sugar found in woody materials and plants. In the new complex carbohydrate, the glucose and xylose are in a linear chain using the same linkages found in cellulose, but the xylose can interfere with the alignment and interaction. Depending on the distribution of glucose and xylose along the chain of sugars, this polysaccharide has the potential to form insoluble fibres, viscous gels or soluble aqueous solutions.

The new complex carbohydrate is found in the roots of barley, but Little said that, at this stage, it is too early to understand its role in the roots’ cell walls.

“We do have some early evidence that the genes involved in its synthesis are turned on in response to a pathogen attack, either from fungal infection or nematodes,” he said. “Perhaps we will find a role for this polysaccharide in the plant defence response in the future. With respect to roots, there is currently work underway to investigate the role of this polysaccharide during root development.”

From a practical standpoint, Little emphasized that plant polysaccharides have numerous applications in industry, each determined by its own physicochemical properties. From a food perspective, he said that the question still remains as to whether this could be utilized as a dietary fibre given that its fermentability throughout digestion is still unknown.

“Our next step is to investigate the amount and tissue distribution of this polysaccharide in other cereals such as wheat, rice, maize and sorghum. Extracting the polysaccharide from each source will allow us to characterize the inherent properties that each structure holds. From here we will be able to identify potential applications and ways to value-add to the crops produced by farmers.”

There is a lot of anticipation for this new complex carbohydrate given that its properties could be manipulated to suit a variety of functions in the future, he said.

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