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The Regulation of Starch Biosynthesis in Barley (Hordeum vulgare)

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Title: The Regulation of Starch Biosynthesis in Barley (Hordeum vulgare)
Author: Ahmed, Zaheer
Department: Department of Molecular and Cellular Biology
Program: Molecular and Cellular Biology
Advisor: Emes, Michael J
Abstract: Starch has enormous uses in the food and non-food industries in different forms. An important form of starch in the food industry is resistant starch (RS). Resistant starches (RS) have potential benefits for human health as a source of low-glycemic carbohydrate and as a prebiotic for the large colon. Such starches are often referred to as high-amylose though this may reflect changes in amylopectin as well the proportion of amylose in the starch granule. This study investigated the relationship between resistant starch (RS) and physical properties of the starch which may contribute to increased RS. The role of protein phosphorylation, and protein complex formation between enzymes of starch synthesis, was also studied in a range of barley genotypes exhibiting high, low and normal amylose phenotypes. In the final part of the thesis, the relationship between variations in starch physiochemical properties and starch granule proteome from genotypes with no known mutations in starch biosynthetic enzymes was investigated. The results indicate that increased RS is positively associated with increased amylose and B-granule content. Detailed biochemical analysis of barley mutants, with alterations in the starch biosynthesis pathway, revealed that formation of phosphorylation-dependent multi-enzyme complexes among isoforms of starch synthases (SS) and branching enzymes (BE) are potentially important mechanisms of regulating RS biosynthesis. Barley lines down regulated with SBEIIa or SBEIIb, demonstrated distinct patterns of protein-protein interactions compared with a reference genotype, suggesting functional complementation for the loss of either isoform by SBEI and SP (starch phosphorylase). In an ssiia mutant no protein complexes were formed indicating that SSIIa plays an important role in recruiting different components into protein complexes. Detailed biochemical analysis revealed that in some of the mutant lines, different protein complexes are involved in the synthesis of A- and B-granules. These variations in protein complexes are reflected in the complement of starch synthesizing enzymes detected in starch granules (A- and B-) of different genotypes. The results reinforced the hypothesis that the multi-enzyme complexes play a functional role in biosynthesis of A- and B-granules. Finally, studies of the physiochemical properties of seed and starch in cultivars with no known mutations in starch biosynthetic enzymes, suggest that significant component of variation lie elsewhere, and are independent of the starch granule proteome.
URI: http://hdl.handle.net/10214/7789
Date: 2014-01
Rights: Attribution-ShareAlike 2.5 Canada


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