The manipulation of fructose 2,6-bisphosphate levels in sugarcane
Date
2006-03
Authors
Hiten, Nicholas Fletcher
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : University of Stellenbosch
Abstract
Fructose 2,6-bisphosphate (Fru 2,6-P2) is an important regulatory molecule in plant carbohydrate
metabolism. There were three main objectives in this study. Firstly, to determine whether the
recombinant rat 6-phosphofructo 2-kinase (6PF2K, EC 2.7.1.105) and fructose 2,6-bisphosphatase
(FBPase2, EC 3.1.3.11) enzymes, which catalyse the synthesis and degradation of Fru 2,6-P2
respectively, showed any catalytic activity as fusion proteins. Secondly, to alter the levels of Fru
2,6-P2 in sugarcane, an important agricultural crop due to its ability to store large quantities of
sucrose, by expressing the recombinant genes. Thirdly, to investigate whether sugar metabolism
in photosynthetic- (leaves) and non-photosynthetic tissue (internodes) were subsequently
influenced.
Activity tests performed on the bacterially expressed glutathione-S-transferase (GST) fusion
6PF2K and FBPase2 enzymes showed that they were catalytically active. In addition antibodies
were raised against the bacterially expressed proteins.
Methods for extracting and measuring Fru 2,6-P2 from sugarcane tissues had to be optimised
because it is known that the extraction efficiencies of Fru 2,6-P2 could vary significantly between
different plant species and also within tissues from the same species. A chloroform/methanol
extraction method was established that provided Fru 2,6-P2 recoveries of 93% and 85% from
sugarcane leaves and internodes respectively. Diurnal changes in the levels of Fru 2,6-P2,
sucrose and starch were measured and the results suggested a role for Fru 2,6-P2 in
photosynthetic sucrose metabolism and in the partitioning of carbon between sucrose and starch in
sugarcane leaves.
Transgenic sugarcane plants expressing either a recombinant rat FBPase2 (ODe lines) or 6PF2K
(OCe lines) were generated. The ODe lines contained decreased leaf Fru 2,6-P2 levels but
increased internodal Fru 2,6-P2 levels compared to the control plants. Higher leaf sucrose and
reducing sugars (glucose and fructose) were measured in the transgenic plants than the control
plants. The transgenic lines contained decreased internodal sucrose and increased reducing
sugars compared to the control plants. Opposite trends were observed for Fru 2,6-P2 and sucrose
when leaves, internodes 3+4 or internodes 7+8 of the different plant lines were compared. In
contrast, no consistent trends between Fru 2,6-P2 and sucrose were evident in the OCe transgenic
lines.
Description
Thesis (MSc (Plant Biotechnology))--University of Stellenbosch, 2006.
Keywords
Dissertations -- Plant biotechnology, Theses -- Plant biotechnology, Sugarcane -- Biotechnology, Sugarcane -- Genetic engineering, Transgenic plants, Fructose-2,6-bisphosphate