碩士 / 國立清華大學 / 生命科學系 / 88 / Abstract:
In this study, cells of Chlorella pyrenoidosa were subjected to heat stress (46.5℃ for 1h) . It was found that the treated cells lost all the chlorophyll when they are cultured again in the growth medium. The culture started to grow and regained its green color several days later. By using flow cytometer, we found that the disappearance of pigments seemed to proceed in two distinguishable steps. The fluorescence intensity dropped up to 2-fold within about 8 h after stress, indicating that the whole cell population uniformly lost a portion of their pigments. In the second step, which started at about 8h after stress, a new peak appeared at a low fluorescence position similar to that of the dead white cells. The number of these white cells increased rapidly, and was accompanied by a decrease in the green cells. The whole process completed within about 24h after stress. Thus in the second step, in which each cell depleted all of its remaining pigments, conversion of the cell was a random process.
In order to study the difference in the resistant to heat stress at different growth period of Chlorella. Synchronous culture was obtained by the light/dark regime. At the beginning of a light period, Chlorella cells of a synchronous culture were small vegetative cells. As the time went on, cells gradually matured. We found that small vegetative cells were more resistant to heat than matured ones. When we elevated the temperature (48.5℃ for 1h), the response of small vegetative cells remained the same one (46.5 1h) in the pigment recovery, but the recovery of matured ones was significantly delayed.
In addition, small cells were used in a serious of experiments studying the conditions required for chlorophyll bleaching during reculture. After heat stress, cells were kept in the dark for a period of time, when reculture Chlorella. We found that the longer the cells stayed in the dark, the less white cells were generated. Take 48 h dark period for example, there were about 80% stayed in green color, and kept on growing. We also changed the light intensity of the reculture period, it was found that at a light intensity lower than 4 mmol/m2s , chlorophyll degradation was slowed down, and the damage was less extensive. From the above results, we conclude: (1) light is needed to trigger the chlorophyll degradation process. (2) after heat stress, light is another stress when reculture cells. If we lower the light intensity, the damage may become less serious. (3) when reculture is kept completely in the dark, the cells may repair the damage due to heat stress.
We also measured the photosynthetic activity of Chlorella during and after heat stress. It was found that photosynthesis was deactived after 10 minutes under heat stress. During reculture in the dark, afterword, cells retained their chlorophyll but without any photosynthetic activity. We suggest that the damage of heat stress on photosynthesis of Chlorella is irreversible.
| Identifer | oai:union.ndltd.org:TW/088NTHU0105007 |
| Date | January 2000 |
| Creators | 曾現鈁 |
| Contributors | 徐邦達 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 76 |
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