1988 Fiscal Year Final Research Report Summary
Metabolism in root nodules and function of leghemoglobin
| Project/Area Number |
62490009
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
広領域
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| Research Institution | Nagoya University |
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Principal Investigator |
YAMAMOTO Yukio Professor, School of Agriculture, Nagoya University, 農学部, 教授 (40022561)
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| Project Period (FY) |
1987 – 1988
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| Keywords | Nodule / Leghemoglobin / Soy bean / Symbiotic nitrogen fixation / Bacteroid / Uricase / Xanthine dehydrogenase / 根粒の代謝 |
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| Research Abstract |
Soybean nodules consist of cells infected and uninfected with Bradyrhizobium japonicum. The infected cells are large and filled with bacteroids. Nitrogen fixation in nodules supposedly proceeds with the interaction between infected and unifected cells. However, the relation of nitrogen-carbon metabolism and mutual supply of nitrogen- and carbon- compounds between both cells are little studied.
Protoplasts were prepared from nodules in several stages of soybean development. Infected cells, uninfected cells and cortex cells could be separated for the measurements of several enzyme activities. Xanthine dehydrogenase activity was found in infected cells. Uricase activity was found in uninfected cells. Phosphoenolpyruvate carboxylase (CO_2 dark fixation) activity was high in uninfected cells. Malic dehydrogenase activity was found in both infected and uninfected cells, but higher in infected cells.
The enzyme distribution indicates that the malate produced in CO_2-dark fixation of uninfected cells will be supplied to the infected cells and the uric acid produced in infected cells will be transported to the uninfected cells, where uric acid is converted to allantoin.
Calcium and boron stimulated nitrogen fixation when they were in optimum concentrations. The in vitro experiments showed that leghemoglobin elevated the respiration of mitochondria and bacteroids even under low oxygen concentrations.
Nitrate supply inhibited nitrogen fixation within 24 hours. The inhibition proceeded in accordance with the production of nitrite from nitrate. Leghemoglobin was converted to nitrosyl-leghemoglobin in the presence of nitrite. The O_2-binding of leghemoglobin was competitively inhigited by nitrite produced from nitrate.
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