Thesis (PhD (Genetics. Plant Biotechnology))--University of Stellenbosch, 2006. / The main aim of the work presented in this thesis was to elucidate the apparent role of
pyrophosphate fructose 6-phosphate 1-phosphotransferase (PFP) in sucrose accumulation
in sugarcane. PFP activity in sugarcane internodal tissue is inversely correlated to the
sucrose content and positively to the water-insoluble component across varieties which
differ in their capacities to accumulate sucrose. This apparent well defined and important
role of PFP seems to stand in contrast to the ambiguity regarding PFP’s role in the general
literature as well as the results of various transgenic studies where neither the downregulation
nor the over-expression of PFP activity had a major influence on the phenotype
of transgenic potato and tobacco plants. Based on this it was therefore thought that either
the kinetic properties of sugarcane PFP is significantly different than that of other plant
PFPs or that PFP’s role in sucrose accumulating tissues is different from that in starch
accumulating tissues.
In the first part of the study sugarcane PFP was therefore purified and its molecular and
kinetic properties were determined. It consisted of two subunits which aggregated in
dimeric, tetrameric and octameric forms depending on the presence of Fru 2,6-P2. Both the
glycolytic and gluconeogenic reactions had broad pH optima and the kinetic parameters for
all the substrates were comparable to that of other plant PFPs. The conclusion was therefore
that sugarcane PFP’s molecular and kinetic characteristics do not differ significantly from
that of other plant PFPs.
The only direct way to confirm if PFP is involved in sucrose accumulation in sugarcane is
to alter its levels in the same genetic background through genetic engineering. This was
therefore the second focus of this study. PFP activity was successfully down-regulated in
sugarcane. The transgenic plants showed no visible phenotype under greenhouse and field
conditions and sucrose concentrations in their immature internodes were significantly
increased. PFP activity was inversely correlated with sucrose content in the immature internodes of the transgenic lines. Both the immature and mature internodes of the
transgenic plants had significantly higher fibre contents.
This study suggests that PFP plays a significant role in glycolytic carbon flux in immature,
metabolically active sugarcane internodal tissues. The data presented here confirm that PFP
can indeed have an influence on the rate of glycolysis and carbon partitioning in these
tissues. It also implies that there are no differences between the functions of PFP in starch
and sucrose storing tissues and it supports the hypothesis that PFP provides additional
glycolytic capacity to PFK at times of high metabolic flux in biosynthetically active tissue.
This work will serve as a basis to refine future genetic manipulation strategies and could
make a valuable contribution to the productivity of South African sugarcane varieties.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/1089 |
| Date | 03 1900 |
| Creators | Groenewald, Jan-Hendrik |
| Contributors | Botha, F. C., 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 | 882248 bytes, application/pdf |
| Rights | University of Stellenbosch |
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