碩士 / 國立清華大學 / 生命科學系 / 90 / In the previous study,we know that Chlorella pyrenoidosa has a characteristicof heat-tolerance.Tzeng (2000)even suggested that cells of Chlorella pyrenoidosa were subjected to heat stress of 46.5℃ for 1h. It found that the heat-treated cells lost all the chlorophyll when they were cultured again in the growth medium.The culture started to grow and regained its green color several days later.By using flow cytometer ,it was found that the disapperence of pigment seemed to proceed in two distinguishable steps .When the Chlororella culture had been kept in the dark after the heat -treatment, the chlorophyll content of cells remained unchanged for up to 5 days.It seemed that darkness protects chlorophyll from degradation.It was found that at a light intensity lower than 4μmolm-2s-1,chlorophyll degradation was slowed down.It concluded (1)Light is needed to trigger the chlorophyll degradation process.(2)After heat stress,light is another stress to the recultured cells ,the lower light intensity the less damage.(3)When culture is kept completely in the dark,the cells may repair the stress due to heat stress.
In this study,we want to further study the physiology and biochemistry of whiting cells and the relationship between heat-tolerance and chlorophyll degradation.It was found that the heat-treated cells lost all the chlorophyll in two distinguishable steps.The first stage starts immediately as soon as the cells were recultivated .The second stage of chlorophyll degradation would start about 4h after recultivation.In the degrading pathway,we can detect chlorophyll partial degrading intermediates. During the chlorophyll degradation,some thylakoid menbrane proteins with specific molecular weight disappeared.(24kD;30kD;50kD). 30kD and 50kD would not be degradated until 4h after reculivation, and 24kD disappered at 8h after recultivation.We suggested the degradation of chlorophyll might be due to the specific thylakoid menbrane proteins degradation.Under microscopy chlorophyll might be seen in the white cells . But when the Chlorella were cultivated under red light
condition(≧630nm ,4.6μmolm-2s-1),the chloroplast would turn to be half . Under the confocal microscopy scanning microscopy ,we could observe clear fluorescence image of chloroplast。
We also measured the photosynthetic activity of Chlorella during heat stress.It was found that photosynthesis was inactivated after 20 minutes of 46.5℃ heat treatment.While lowering temperature to 40℃,the photosythesis would little affected by heat. We found that the more rapidly disappeared of photosynthesis,the more green cells turned to white cells.
We suggested that heat stress(46.5℃ for 1h ) make photosynthesis activity disappear rapidly,and the more rapidly photosynthesis disappears ,the more green cells turned to white cells.And continuous illumination might cause oxdative stress in cells and break up the protection system of the cells ,leading green cells turn to white cells.
| Identifer | oai:union.ndltd.org:TW/090NTHU0105037 |
| Date | January 2002 |
| Creators | Wu, Hsin Hsin, 吳欣欣 |
| Contributors | Hsu, Ban-Dar, 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 | 71 |
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