| Summary: | 碩士 === 國立中山大學 === 海洋生物研究所 === 99 === Microalgae are an important potential feedstock for biodiesel production. Understanding the physiology of lipid biosynthesis in microalgae is pivotal to microalgal aquaculture management. A freshwater green microalga strain, UTEX 2219-4, was isolated from UTEX 2219 which was reported containing two strains. Its ITS sequences are closely related to those in the family of Scenedesmaceae in the GenBank. Nitrogen starvation, salt stress and osmotic stress greatly enhanced lipid biosynthesis in this strain, while combination of nitrogen deficiency and osmotic stress had the most dramatic effect. Chloroplast was condensed and photosynthesis efficiency declined about 50% after 3 days of nitrogen starvation. Chlorophyll degradation followed the same trend but was more severe than the reduction of photosynthesis efficiency. Oil body formation was not observed in the cells kept in the dark under nitrogen starvation, suggesting photosynthesis rather than autophagy is the major player in oil body formation. Under non-saturation levels of light intensities coupled with nitrogen starvation, the oil body formation under 150 μmol/m2s light intensity was more efficient than that under 75 μmol/m2s. DCMU blocked photosynthesis as well as oil body formation, supporting that the energy for oil body formation was mostly from photosynthesis rather than autophagy during nitrogen starvation.
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