碩士 / 國立臺灣大學 / 植物學研究所 / 90 / With a surface area of ca. 100 ha, the Lake Li-Yu is the largest lake in Hwa-Lian county, Taiwan. It is an eutrophic lake with Botryococcus braunii blooms occurred in autumn and winter in the years of 1993, 1996 and 1999. Death of fish, mainly Tilapia, were observed in the lake during B. braunii blooming. In order to elucidate the effects of algal blooms in this aquatic ecosystem, the toxicity of B. braunii was studied. Fifteen strains of phytoplankton were isolated from the lake and the cultures were tested for the toxicity of B. braunii extract on them. Results showed that except Microcystis flos-aquae and Oocystis parva, all other species exhibited various degrees of sensitivity to B. braunii. Population analysis of the tested species in the lake showed that the sensitivity to B. braunii was closely correlated with the abundance of these phytoplankton species in the lake during Botryococcus blooming. Toxic effects of B. braunii extract were also observed to the zooplankton collected from the Lake. In them, copepods showed higher sensitivity to crude extracts from B. braunii than cladocerans. All of these results suggest that B. braunii might play an allelopathic effect on other plankton.
In batch culture, the toxicities of B. braunii were enhanced when P- or N-nutrient became a limitation. The maximum toxicity was measured when the growth of cells was near the end of exponential growth phase. Under this condition, the nutrient concentrations in culture medium were close to those measured during B. braunii bloom, suggesting that the chemical environment in the Lake Li-Yu might create a favorable condition for B. braunii to survive and to compete with other plankton species.
The fractions containing active substances of B. braunii were soluble in organic solvents. Further isolation, purification, and identification of active substances, by employing TLC, HPLC, NMR, and GC-MS techniques, indicated that they were fatty acids, including palmitic acid (16:0), oleic acid (18:1ω9), linoleic acid (18:2ω6) and α-linolenic acid (18:3ω3). The highest toxicity was revealed in C18-unsaturated fatty acids whose EC50 (or LC50) were found between 10-20μg‧mL-1 against phytoplankton as well as against zooplankton. Total free fatty acid content might be as high as 2.25% of dry weight, which was much higher than other 7 tested species of cyanophytes, chlorophytes and dinophytes.
Addition of B. braunii extract inhibited the photosynthetic electron flow of tested algal cells, while the respiration rate was affected little. Similar effects were also observed when C18-unsaturated fatty acids were added to the algal cultures. It is noteworthy that the tested cells would die even when the added concentrations were lower than IC50 value of inhibition of photosynthesis. However, the photosynthetic electron flow inhibitor, DCMU, did not cause the death of tested algal cells within 24 hrs. This implicates that the inhibition of electron flow was not the only cause of death B. braunii exerted to other algal species.
It was observed that addition of C18-unsaturated fatty acids to algal cultures caused a remarkable K+-leakage from tested cells within 30 minutes. The amount of released K+ might as high as 5-10% of total K+ in the cells. Enzymatic assays of ATPase showed that C18-unsaturated fatty acids did inhibit P-type, but not V- or F-type ATPase of the tested algal cells. Because P-type ATPase (especially H+-ATPase) is related to the maintenance of membrane potential, inhibition of this type of membrane enzyme might be attributed to K+-leakage from the cells. C18-unsaturated fatty acids did not exert inhibitory effect on V-, F-, or other P-type ATPase, but on Na+/K+-ATPase of copepods and cladocerans. It is assumed that toxic effects of B. braunii on crustacean zooplankton might be related to the interference of osmoregulation through inhibiting the Na+/K+-ATPase activity.
| Identifer | oai:union.ndltd.org:TW/090NTU00366027 |
| Date | January 2002 |
| Creators | Chiang, Yin-Ru, 江殷儒 |
| Contributors | Wu, Jiunn-Tzong, 吳俊宗 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 0 |
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