Chemical interrogation: a new 'systems' approach to starch metabolism in germinating barley seeds.

Lead Research Organisation: University of East Anglia


The aim of this project is to provide information that will help in the breeding of new, improved types of wheat and barley for food and for brewing. Wheat and barley are two of the most important food crops in the UK. Wheat seeds are ground to produce flour for bread, biscuits, pastry and sauces. Barley seeds are partially germinated to produce malt, which is then incubated with yeast to yield alcohol for beer and whisky production. Wheat and barley seeds contain up to 80% of their dry weight as starch. This starch is normally broken down to sugars when the seeds germinate, and the sugars are used by the embryo of the seed for growth to produce the new seedling. The timing and extent of starch breakdown in the seed has very important implications for the production of both wheat flour and barley malt. The quality of wheat seeds for the production of flour depends on a high starch content. In a wet summer, the process of starch breakdown can start while the seed is still on the plant, resulting in a very poor quality of flour. This was a massive problem in the UK in 2004. Very large amounts of wheat seed had to be imported for the food industry because UK wheat was not of adequate quality. The process of barley malting depends on precise control of starch breakdown, so that when yeast is added the correct amount of sugar is available for alcohol production. In spite of years of breeding for the 'ideal' barley for making malt, brewers still see room for improvement. Efforts to improve the quality of wheat and barley seeds are held up by a lack of knowledge about how starch is broken down in these seeds. This process is carried out by enzymes, and although a lot is known about some of the individual enzymes we do not know how they operate together inside the seed. Our aim is to use new scientific techniques that can provide a clearer picture of what happens inside the germinating seed. We want to discover which enzymes are needed for starch breakdown, and exactly what they contribute to this process. We will do this by soaking the germinating seeds in specific chemicals that can prevent the actions of some of the enzymes, and by looking for mutant barley plants in which some of the enzymes are missing from the seeds. We will investigate how starch breakdown is altered in the chemically-treated and mutant seeds. This will give us new information about the processes inside seeds, and will enable us to advise wheat and barley breeders on producing better wheat and barley crops in the future.

Technical Summary

The capacity for starch degradation in wheat and barley seeds is a major determinant of crop quality. In wheat, unfavourable conditions during seed maturation can cause premature, pre-harvest production of starch-degrading enzymes that reduces flour quality. In barley, the development of activities of starch-degrading enzymes during malting determines the yield and quality of malt for whisky and beer production. In spite of the importance of starch degradation, the process itself is relatively poorly understood. Much is known about the control of gene expression of some of the enzymes involved, and about the structures and kinetic properties of individual classes of enzymes, but the precise contribution made by each enzyme in determining the rate and nature of starch degradation in the germinating seed remains obscure. Adopting a 'systems' approach, our project will use parallel chemical- and reverse-genetics approaches to produce a systematic and comprehensive picture of the process of starch degradation in the germinating seed. This will provide a new source of information to underpin future progress in wheat and barley breeding. In the main chemical genetics approach, we will design and exploit a small library of substituted small carbohydrate molecules to discover and develop new, class- and isoform-specific inhibitors for enzymes known or suggested to be important in starch degradation in barley seeds. These will be applied to germinating barley seeds to discover the importance of the targeted enzymes in starch degradation. The library will also be applied directly to germinating barley seeds, to discover novel inhibitors of starch degradation that will reveal previously-unknown facets of this process. In the complementary, reverse genetics approach we will isolate five classes of barley mutants lacking specific enzymes believed to be important in starch degradation, and compare germination phenotypes with those from inhibitor applications. The information from these two approaches will be brought together to develop a model of the process of starch degradation within the barley seed. This, together with the inhibitors and mutants generated in the project, will be made available for other research on fundamental and applied aspects of cereal seed germination and on enzymes of carbohydrate metabolism.


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