Citrate Synthase Messenger RNA in Relation to Enzyme Synthesis in Euglena
The unicellular biflagellate Euglena gracilis is unusual amoungst eukaryotes in being able to thrive both as a phototroph in the light and as an organotroph in the dark, and rapidly adjusts its cellular machinery to accommodate a utilizable energy source most efficiently1. For example dark grown cells possess undifferentiated proplastids which develop into functional chloroplasts on exposure to light2. The associated cellular changes during chloroplast development can be conveniently studied in dark grown non-dividing cells maintained on a “resting” medium lacking exogenous carbon and nitrogen3. Upon illumination of resting cells there is a 12 hour lag in chloroplast development followed by a period of rapid proplastid differentiation over 72 hours3. During the lag phase an immediate transcient increase in the specific activities of enzymes of the Tricarboxylic Acid (TCA) cycle is observed4,5, which may furnish the cell with the necessary reductant and substrate energy during chloroplast development. The mitochondrial enzyme citrate synthase is of particular interest since it occupies a key position, regulating the entry of carbon into the TCA cycle6. Cannons and Merrett7 demonstrated that increased citrate synthase (CS) activity was proportional to an increase in enzyme protein but was not reflected in enhanced levels of translatable CS mRNA. This would suggest that control of enzyme activity operates primarily at a posttranscriptional level.
KeywordsChloroplast Development Euglena Gracilis Functional Chloroplast Dark Grown Cell Plasmid Cloning Vector
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