Exploiting genetic variation in barley to elucidate factors determining starch granule morphology in the cereal endosperm
Embargoed until 2025-05-16
Author
Date
2024Type
- Doctoral Thesis
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Abstract
Plants polymerize simple sugars into starch that is stored as water-insoluble, semi-crystalline starch granules. It is present in the form of transitory starch located in the chloroplasts of leaves as a product of photosynthesis and as storage starch accumulated in the amyloplasts of seeds and tubers, including our staple crop plants. While transitory starch granules show similar morphologies across organisms, storage starch granules display a wide variety of morphologies, depending on the biological origin, cellular location, and environmental influences. This storage starch is central to human nutrition, as it is the most important source of carbohydrates in the human diet and for feeding our livestock. A major source of starch originates from cereal grains. These store starch in a specialized storage tissue, i.e. the endosperm, which is used to fuel seedling growth after germination. Despite having a similar chemical composition, starch granules differ markedly in shape, size, and distribution among cereal species.
Barley (Hordeum vulgare L.) is one of the most important cereal crops, ranking fourth in world production, and is mainly used for animal feed and as a raw material for beer production. The starch granules found in barley grains have a bimodal size distribution: larger A-granules (ø 8–25 μm) have a lenticular shape, while smaller B-granules (ø 1–8 μm) are near-spherical. The latter contributes 80–90% to the total starch granule number and only 10–15% to the total starch weight. A-granule count is typically below 10% and contributes due to its volume with 85–90% to the total starch amount. The two types of barley starch granules are characterized by different physicochemical properties, which influence industrial applications.
In this thesis, I sought to explore the genetic factors underlying the bimodal distribution of starch granules in barley. In the first part, I successfully established two high-throughput screening methods to monitor starch granule size distribution, which is applicable to various tissues and species. Those methods enabled me to analyze mutants of some of the known starch synthesis genes in the model barley, investigating their impact on granule morphology and starch properties, and their tissue specificity. And lastly, I investigated the genetic factors underlying the starch granule size distribution in an elite barley population. Show more
Permanent link
https://doi.org/10.3929/ethz-b-000673273Publication status
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Contributors
Examiner: Zeeman, Samuel C.
Examiner: Gruissem, Wilhelm
Examiner: Waugh, Robbie
Examiner: Braumann, Ilka
Publisher
ETH ZurichOrganisational unit
03707 - Zeeman, Samuel C. / Zeeman, Samuel C.
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