Control of symbiotic nitrogen fixation in Rhizobia regulation of NH4 assimilation |
| |
Authors: | Fergal O''Gara K.T. Shanmugam |
| |
Affiliation: | Plant Growth Laboratory, Department of Agronomy and Range Science, University of California, Davis, Calif. 95616 U.S.A. |
| |
Abstract: | The metabolic fate of gaseous nitrogen (15N2) fixed by free-living cultures of Rhizobia (root nodule bacteria) induced for their N2-fixation system was followed. A majority of the fixed 15N2 was found to be exported into the cell supernatant. For example, as much as 94% of the 15N2 fixed by Rhizobium japonicum (soybean symbiont) was recovered as 15NH4+ from the cell supernatant following alkaline diffusion. Several species of root nodule bacteria also exported large quantities of NH4+ from l-histidine. Evidence is presented that overproduction and export of NH4+ by free-living Rhizobia may be closely linked to the control of several key enzymes of NH4+ assimilation. For instance, NH4+ was found to repress glutamine synthetase whereas l-glutamate repressed glutamate synthase. Assimilation of NH4+ as nitrogen source for growth of Rhizobia was inhibited by glutamate. The mechanism of regulation of NH4+ production by root nodule bacteria is discussed. |
| |
Keywords: | |
本文献已被 ScienceDirect 等数据库收录! |
|