| Summary: | 碩士 === 國立中興大學 === 生命科學系所 === 97 === Reactive oxygen species (ROS) have been considered as by-products of aerobic metabolism,where the toxic reactive oxygen tend to increase in plants by stressful conditions. Abiotic stresses such as salinity ,UV and drought will lead to increase ROS and free radical accumulation. To cope with these stresses, plants have been developed a series of defense mechanisms and detoxification systems including ascorbate-glutathione cycle.
A mercuric ion binding protein (MerP) originated from the mer operon of transposon TnMERI1 from Minamata Bay isolated Bacillus megaterium strain MB1 has been studied. The MerP protein was suggested as a membrane bound protein and located in outer membrane with 21 amino acids signal peptides. In previous studies showed that the transgenic plant expressing the MerP protein show higher heavy metal (Cu2+, Cd2+, Pb2+) adsorption ability and tolerance. Result from the thiol groups, the coordination to vicinal cysteines is the dominant mechanism for metal binding. Since the thiol groups could be oxidized to form disulfide bond, and release electrons to eliminate free radical,MerP protein has shown better ROS scavenging ability while it was compared to glutathione.
The result show that MerP transgenic plant showed higher tolerance to salinity, drought and UV-B than wild type. In 100 mM NaCl-mediated stress,the SOD activity of transgenic plant was 9.67％ lower than wild type. Furthermore, the total protein from transgenic plant performed free radical scavenging ability was 2.29% higher than wild type in DPPH• solution. The ROS production detection using H2DCF-DA probe proved that transgenic plant produced weaker fluorescence when compared to the wild type in 100mM NaCl mediated stress, The results suggested that transgenic plant possess the higher ability for scavenging radicals. These studies prove that the MerP protein not only plays an important role in the heavy metal detoxication, when plants experience oxidative stress,but also could scavenge reactive oxygen species, improving the plant growth in the environmental stress.
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