The glyoxylate cycle is a key step in the conversion of storage lipids to sugars in germinating oilseeds. This conversion is thought to allow seedling growth prior to the development of photosynthetic organs. The glyoxylate cycle is thought not only to operate during this stage of development but also during senescence, starvation, pollen development and embryogenesis. It is not known how important the cycle is for plant physiology and development. Two enzymes isocitrate lyase (ICL, EC 4.1. 3.1 ) and malate synthase (MS, EC 4. 1. 3. 2), are central to the cycle. In order to elucidate the function of the glyoxylate cycle in plant development, it was proposed that the synthesis of MS and ICL be inhibited in transgenic plants transformed with chimaeric antisense <I>Ms </I>or <I>Icl </I>genes. Two plant species each offering specific advantages, <I>Nicotiana plumbaginifolia </I>and <I>Solanum tuberosum, </I>were selected for these experiments. Partial <I>Ms </I>and <I>Icl</I> cDNA fragments from both species were isolated and cloned. These were used to construct plant transformation plasmids in which each cDNA fragment was in the antisense orientation with respect to the CaMV 35S promoter. Transgenic <I>N. plumbaginifolia </I>and <I>S. tuberosum </I>plants were regenerated from tissue transformations using strains of <I>Agrobacterium tumefaciens </I>carrying the respective plasmids. The presence of either transgene did not detectably interfere with fertility, germination or post-germination growth in <I>N. plumbaginifolia.</I> In addition to the <I>Ms</I> and <I>Icl </I> mRNAs, the majority of <I>N. plumbaginifolia </I>transformants synthesised a transcript not detected in non-transformants, which was shown in antisense <I>Ms</I> transformants to be antisense RNA complementary to the <I>Ms</I> cDNA fragment. Despite the abundance of antisense RNA in some transformants, neither the steady-state levels of target gene mRNA, nor MS enzyme activities, were significantly affected. The relevance of these results to the mechanism of antisense inhibition is discussed. Evidence was obtained that suggests that the expression of <I>Ms</I> and <I>Icl</I> is influenced by multiple factors.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:641340 |
| Date | January 1996 |
| Creators | Barrett, Matthieu D. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/10742 |
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