Bibliography: leaves 72-77. / Jasmonic acid (JA) is a plant hormone with diverse functions, ranging from development to stress responses. Moreover, a role for JA in mediating defence against pathogen attack has been established, seemingly specific against necrotrophic pathogens such as Botrytis cinerea. Despite these known roles of JA, it is not known exactly how JA activated downstream responses, such as induced gene expression. To further our understanding of JA signalling, this work aimed to identify new components involved in JA signal transduction. A novel screening method based on lack of anthocyanin accumulation after exogenous application of the methyl ester of JA, methyl jasmonate (MeJA), was employed. A recessive, monogenic mutant, jasmonic acid modified2 (jam2), was isolated from T-DNA activation tagged lines and characterized genetically and phenotypically. jam2 was found not to be T-DNA tagged as the T-DNA segregates independently of the mutation. jam2 is unlikely to be an anthocyanin biosynthetic mutant but shows delayed anthocyanin accumulation after exogenous MeJA treatment. Resistance to MeJA root growth inhibition is a phenotype shared by all JA insensitive mutants. Contrary to this, jam2, like Col-0, exhibits stunted root growth on MeJA. The expression of the antifungal peptide, PDF1.2 can be induced by exogenous MeJA treatment. To assess how PDF1.2 expression was affected in jam2, plants were treated with external liquid and vaporous MeJA. Interestingly, the PDF1.2 expression pattern after MeJA application (liquid or gaseous) was biphasic for Col-0, jam2 and jar1. However, compared to Col-0 and jar1, jam2 appeared to be affected in the first induction peak upon liquid MeJA treatment, whilst in the second after gaseous treatment. PDF1.2 expression can also be seen as a marker for JA-mediated defence responses. Upon infection with B. cinerea, jam2 and jar1 showed intermediate resistance and faster PDF1.2 expression, compared to Col-0 and coil-1. These findings suggest that jam2 is possibly involved in temporal regulation of anthocyanin accumulation and PDF1.2 expression after MeJA application and B. cinerea infection. Therefore, jam2 may define a novel component within the JA signalling pathway and further genetic and phenotypic characterisation could confirm this.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uct/oai:localhost:11427/8590 |
| Date | January 2003 |
| Creators | Sanderson, Micheline |
| Contributors | Denby, Katherine J |
| Publisher | University of Cape Town, Faculty of Science, Department of Molecular and Cell Biology |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Master Thesis, Masters, MSc |
| Format | application/pdf |
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