碩士 / 國立嘉義大學 / 水產生物學系碩士班 / 93 / Metallothioneins (MTs) are a family of small proteins having molecular weights of 6~10 kDa, and they are found in certain eukaryotic microorganisms and in the animal kingdom. Their expression can be induced by heavy metals and free radicals. One of their physiological functions is heavy metal detoxification since MT expression appears to be dose and time dependent upon heavy metal treatment. The objective of this study was to determine the functions of MT in the hard clam (Meretrix lusoria). First, the amino acid sequence of MT was cloned and a specific primer was designed for MT mRNA measurements using real-time PCR. To determine the relationship between MT mRNA relative quantity (RQ) levels and cadmium accumulation, hard clams were exposed to 50 (low-dose experiment), 200 (mid-dose experiment), and 1000 μg/L cadmium (high-dose experiment) for 1, 3, 5, and 7 days. Finally, the percentage of cadmium bound by the heavy metal protein was measured. The following results were obtained. (1) The chemical characteristics of MT in the hard clam were similar as those reported for others organisms. It appeared to be cysteine rich and contained 76 amino acids. (2) MT mRNA expression appeared to have a dose response upon cadmium treatment for 1, 3, 5, and 7 days, but it was not time dependent with 50~1000 μg/L cadmium treatment. (3) A positive relationship was found between cadmium accumulation and RQ levels of MT mRNA with treatment using various doses of cadmium. But there was also no relationship with the time course. (4) Most cadmium was bound to the heavy metal protein (70%~95%) after the clams were challenged with cadmium except for those treated with 200 μg/L cadmium for 3 days. The CV% (coefficient of variation) levels were higher after the mid- and high-dose compared to the low-dose cadmium treatment.
In summary, we suggest that the MT mRNA expression is related to cadmium accumulation, but it was limited by the resistance to cadmium in individual clams.
| Identifer | oai:union.ndltd.org:TW/093NCYU0613002 |
| Date | January 2005 |
| Creators | Yi-Ting Chang, 張依庭 |
| Contributors | Su-Mei Wu, 吳 淑 美 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 68 |
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