In order to understand and manipulate carbon flux to sucrose one needs to consider not only
its biosynthetic pathways, but also the competing sinks for carbon in various parts of the
plant and at different stages of development. The cell wall and sucrose is known to be the
major sinks for carbon in young and mature tissues of sugarcane. UDP-Glucose is a central
metabolite in the synthesis of both sucrose and most of the cell wall polysaccharides
(including cellulose, hemicellulose and pectic polymers) and manipulation of the flux into
either of the cell wall components could therefore cause an increase of flux toward one or
more of the competing sinks. In the present study UDP-Glucose dehydrogenase (UGD)
activity was chosen for down regulation as it catalyzes the rate limiting step in the
biosynthesis of the precursors of both hemicellulose and pectin, a major competing sink for
assimilated carbon.
Transgenic sugarcane lines with repressed UGD activity showed significantly increased
sucrose accumulation in all internodes which was highly correlated with reduced UGD
activity. Sucrose phosphate synthase had increased activation which suggests an alteration
in carbon flux toward sucrose.
The reduction of carbon flux through UGD was compensated for by an increase in the
activity of the myo-inositol oxygenation pathway (MIOP), an alternative pathway for the
synthesis of cell wall matrix precursors. The increased activity of the MIOP resulted in
increased total uronic acids and pentoses in the cell wall. Total cell wall glucose was also
increased which is a further indication of altered carbon metabolism.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/1259 |
| Date | 03 1900 |
| Creators | Bekker, Jan P. I. |
| Contributors | Kossmann, J. M., University of Stellenbosch. Faculty of Agrisciences. Dept. of Genetics. Institute for Plant Biotechnology (IPB) |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 803741 bytes, application/pdf |
| Rights | University of Stellenbosch |
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