| Research Abstract |
In cotyledons of some fatty seedlings such as pumpkin and Arabidopsis, microbody transition from glyoxysomes to leaf peroxysomes is observed during greening. Reverse transition from glyoxysomes to leaf peroxisomes occurs during senescence of the cotyledons. It has been suggested that the functional conversion between glyoxysomes and leaf peroxisomes is controlled at various levels, such as gene expression, protein translocation and protein degradation. A genetically approach may be an effective strategy toward understanding the regulatory mechanism(s) underlying the microbody transition at the molecular level. We screened 2,4-dichIorophenoxybutyric acid (2,4-DB)-resistant mutants that have defects in glyoxysomal function.
It has been previously demonstrated that 2,4-DB is metabolized to produce a herbicide, by the action of glyoxysomal fatty acid β-oxidation in higher plants. In order to isolate mutants that have defects in glyoxysomal fatty acid β-oxidation, mutant lines of Arabidopsis
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seedlings were screened for growth in the presence of toxic levels of 2,4-DB. Twelve of the mutants survived and of these, four required sucrose for post-germinative growth. This result suggests that these mutants have defects in glyoxysomal fatty acid β-oxidation, since glyoxysomal fatty acid β-oxidation has an important role in converting sucrose from storage lipids during germination. One of the mutants lacks thiolase protein, an enzyme involved in fatty acid β-oxidation during germination and subsequent seedling growth. Another mutant has a defect in the intracellular transport of thiolase form the cytosol to glyoxysomes. Etiolated cotyledons of both mutants have glyoxysomes with abnormal morphology. In the thiolase defective mutants, glyoxysomes have tubular structures that contain many vesicles. Interaction between glyoxysomes and lipid bodies and the transport of lipids from lipid bodies to glyoxysomes during fatty acid β-oxidation are studied by using the electron microscopic analysis of the mutants. Less
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