| Project/Area Number |
14360037
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Plant nutrition/Soil science
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| Research Institution | Tohoku University |
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Principal Investigator |
MINAMISAWA Kiwamu Tohoku University, Graduate School of Life Sciences, Professor, 大学院・生命科学研究科, 教授 (70167667)
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| Co-Investigator(Kenkyū-buntansha) |
鮫島 玲子 東北大学, 大学院・生命科学研究科, 日本学術振興会特別研究員
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| Project Period (FY) |
2002 – 2004
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| Project Status |
Completed (Fiscal Year 2004)
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| Budget Amount *help |
¥14,900,000 (Direct Cost: ¥14,900,000)
Fiscal Year 2004: ¥2,500,000 (Direct Cost: ¥2,500,000)
Fiscal Year 2003: ¥2,600,000 (Direct Cost: ¥2,600,000)
Fiscal Year 2002: ¥9,800,000 (Direct Cost: ¥9,800,000)
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| Keywords | Bradyrhizobium japonicum / denitrofication / nitrous oxide(N_2O) / nosZ / symbiosis / soybean / 亜酸化窒素 / ^<15>N |
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| Research Abstract |
Denitrification is anaerobic respiration using nitrate (NO_3^-), nitrite (NO_2^-), nitric oxide (NO), and nitrous oxide (N_2O) as terminal electron acceptors. Nitrous oxide (N_2O) is a key atmospheric greenhouse gas that contributes to global climatic change through radiative warming and depletion of stratospheric ozone. Agricultural lands are one of major sources, and significantly contribute the net increase in atmospheric N_2O. We used N_2, which has a natural abundance of ^<15>N (0.366 atom%), as a carrier gas in a gas chromatograph with a thermal conductivity detector to detect ^<15>N-N_2 quantitatively. When Bradyrhizobium japonicum USDA110 was cultured anaerobically in medium containing ^<15>N-NO_3, ^<15>N-N_2 was detected stoichiometrically. Analysis of 63 bradyrhizobial isolates revealed that denitrification ability varied with field site. To examine whether nos gene cluster of Bradyrhizobium japonicum is responsible for N_2O reduction in symbiosis, we constructed a nosZ delet
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ion mutant of B.japonicum USDA110. The activity of N_2O reductase was determined by N_2O uptake and conversion of ^<15>N_2O into ^<15>N_2. Free-living cells of USDA110 showed N_2O reductase activity, while nosZ mutant did not. Complementation of cosmids containing nos gene cluster of B.japonicum USDA 110 to the nosZ mutant restored the N_2O rductase activity, indicating nosZ-dependent N_2O reductase activity and validity of the mutant. When the detached soybean nodules formed with wild-type USDA110 was fed with ^<15>N_2O, the nodules rapidly emitted ^<15>N_2 outside at a ratio of approximately 98.5% of ^<15>N-N_2O uptake. On the other hand, nosZ mutant-inoculated nodules did not mediate the conversion of ^<15>N_2O to ^<15>N_2 at all. Moreover, substantial decrease of N_2O concentration was detected in the rhizosphere of intact soybean plant inoculated with wild-type USDA110. These results demonstrate that the conversion of N_2O to N_2 depends exclusively to the function of nos gene cluster, and soybeans nodulated with B.japonicum carrying nos cluster are able to remove N_2O gas in rhizosphere environments Less
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