微藻是生質柴油的重要潛在來源之一。瞭解微藻的脂質合成之調控機制有助於生質柴油的生產管理。本研究室從UTEX 2219中分離出一株淡水綠藻並命名為UTEX 2219-4。以它的 internal transcribed spacers（ITS）序列做親緣關係研究，結果顯示這株綠藻與 Scenedesmaceae科中物種較為相近。缺氮、高鹽及滲透壓逆境使UTEX 2219-4的脂質含量快速上升，而以缺氮及滲透壓逆境併用之效果最好。光合作用效率及總葉綠素含量在缺氮下快速下降。在缺氮及黑暗中，UTEX 2219-4沒有油粒體形成。在缺氮及不飽和照度下，UTEX 2219-4的油粒體在150 μmol/m2s之下多於在75 μmol/m2s下，而DCMU（3-(3,4-dichlorophenyl)-1,1-dimethylurea）阻斷了油粒體的形成。以上結果顯示生成油粒體的能源主要來自光合作用，而非從自噬作用的生理調節而來。

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.

Foreword i
Acknowledgements i
Letter of Acceptance for Publication ii
摘要 iii
Abstract iv
Contents v
List of Figures vi
List of Tables vii
1. Introduction 1
2. Materials and Methods 3
3. Results and Discussion 8
4. References 15
Figures 18
Tables 24
Appendix 25

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