Thesis (MSc (Plant Biotechnology))--University of Stellenbosch, 2007. / Sugarcane is cultivated because of the high levels of sucrose it stores in its
internodes. Starch metabolism has been a neglected aspect of sugarcane research
despite the problems caused by it during sugarcane processing. Currently there is no
information available on the starch content in different South African commercial
sugarcane varieties. This project had two main aims of which the first was to
determine the starch content in the internodal tissues of six commercial sugarcane
varieties. The activities of ADP-Glucose Pyrophosphorylase (AGPase) and β-
amylase were also determined. The second aim of the project was to manipulate
starch metabolism in sugarcane using transgenesis. To achieve this, transformation
vectors for the down-regulation of AGPase activity and over-expression of β-amylase
activity were designed. These vectors were then used to transform sugarcane calli
and the results were analysed in suspension cultures. Starch levels in sugarcane
internodal tissue increased more than 4 times from young to mature internodes.
There were also large differences between varieties. When mature tissues of
different varieties were compared, their starch concentration varied between 0.18
and 0.51 mg g-1 FW, with the majority of the varieties having a starch concentration
between 0.26 and 0.32 mg g-1 FW. NCo376’s starch concentration was much lower
than the rest at 0.18 mg g-1 FW and N19’s was much higher at 0.51 mg. g-1 FW.
There was also a very strong correlation between starch and sucrose concentration
(R2 = 0.53, p ≤ 0.01) which could be due to the fact that these metabolites are
synthesized from the same hexose-phosphate pool. No correlation was evident
between starch concentration and AGPase activity. This was true for correlations
based on either tissue maturity or variety. β-amylase activity expressed on a protein
basis was almost 5 times higher in the young internodes compared to mature internodes, suggesting that carbon might be cycled through starch in these
internodes. AGPase activity in the transgenic suspension cultures was reduced by
between 0.14 and 0.54 of the activity of the wild type control. This reduction led to a
reduction in starch concentration of between 0.38 and 0.47 times that of the wild type
control. There was a significant correlation between the reduction in AGPase activity
and the reduction in starch (R2 = 0.58, p ≤ 0.05). β-amylase activity in the transgenic
suspension cultures was increased to 1.5-2 times that of the wild type control. This
led to a reduction in starch concentration of between 0.1 and 0.4 times that of the
wild type control. Once again the increase in β-amylase activity could be correlated to
the reduction in starch concentration of the transgenic suspension cultures (R2 =
0.68, p ≤ 0.01). In both experiments there was no significant effect on sucrose
concentration.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/2880 |
| Date | 12 1900 |
| Creators | Ferreira, Stephanus Johannes |
| Contributors | Groenewald, J-H., Lloyd, J. R. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 825429 bytes, application/pdf |
| Rights | University of Stellenbosch |
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