期刊
MICROBES AND ENVIRONMENTS
卷 23, 期 3, 页码 215-220出版社
JAPANESE SOC MICROBIAL ECOLOGY, DEPT BIORESOURCE SCIENCE
DOI: 10.1264/jsme2.23.215
关键词
Bradyrhizobium japonicum; NAD-malic enzyme; symbiotic nitrogen fixation; soybean nodules
The NAD(+)-dependent malic enzyme (DME) has been reported to play a key role Supporting nitrogenase activity in bacteroids of Sinorhizobium meliloti. Genetic evidence for a similar role in Bradyrhizobium japonicum USDA110 was obtained by constructing a dine mutant. Soybean plants inoculated with a dme mutant did not show delayed nodulation, but formed small root nodules and exhibited significant nitrogen-deficiency symptoms. Nodule numbers and the acetylene reducting activity per nodule as a dry weight value 14 and 28 days after inoculation with the dme mutant were comparable to those of plants inoculated with wild-type B. japonicum. However, shoot dry weight and acetylene reducting activity per nodule decreased to ca. 30% of the values in plants with wild-type B. japonicum. The sucrose and organic acid (malate, succinate, acetate, alpha-ketoglutarate and lactate) contents of the nodules were investigated. Amounts of sucrose, malate and alpha-ketoglutarate increased on inoculation with the dine mutant, suggesting that the decreased DME and nitrogenase activities in the bacteroids resulted in a reduction in the consumption of these respiratory metabolites by the nodules. The data suggest that the DME activity of B. japonicum bacteroids plays a role in nodule metabolism and supports nitrogen fixation.
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