Glutamine synthetase (GS) is a key enzyme in nitrogen (N) assimilation, especially during seed development. This thesis has identified three cytosolic GS isoforms (HvGS1) in barley (Hordeum vulgare L. cv Golden Promise). The quantitation of gene expression, isoform localisation and response to N supply has revealed that each gene plays a non-redundant role in different tissues throughout seedling development. The localisation of HvGS1_1 in vascular cells of different tissues, combined with its abundance in the stem and its response to changes in N supply, indicate that HvGS1_1 is important in N transport and remobilisation. HvGS1_1 is located on chromosome 6H at 72.54 cM, close to the marker HVM074 which is associated with a major quantitative trait locus (QTL) for grain protein content (GPC). HvGS1_1 may be a potential candidate gene to manipulate barley GPC. HvGS1_2 mRNA was localised to the leaf mesophyll cells, in both the cortex and the pericycle of roots and was the dominant HvGS1 isoform in these tissues. HvGS1_2 expression increased in the leaves with an increasing supply of N, suggesting that its role is in the primary assimilation of N. HvGS1_3 was specifically and predominantly localised in the grain, being highly expressed throughout grain development. HvGS1_3 expression increased specifically in the roots of plants grown on high NH₄⁺ suggesting that it has a primary role in grain N assimilation and also in the protection from ammonium toxicity in roots. The expression of the HvGS1 genes is directly correlated with both protein and enzymatic activity, indicating that transcriptional regulation is of prime importance in the control of GS activity in barley. Analysis of 15 different barley cultivars found no correlation between HvGS expression and various desirable attributes. Transgenics which over-express and silence individual HvGS1 isoforms have been produced and confirmed, to analyse for changes in beneficial traits.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:574853 |
| Date | January 2013 |
| Creators | Goodall, Andrew James |
| Contributors | Tobin, Alyson |
| Publisher | University of St Andrews |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/10023/3746 |
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