title: NAD-Malic Enzyme Affects Nitrogen Fixing Activity of Bradyrhizobium japonicum USDA 110 Bacteroids in Soybean Nodules.
abstract: 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 dme 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, α-ketoglutarate and lactate) contents of the nodules were investigated. Amounts of sucrose, malate and a-ketoglutarate increased on inoculation with the dme 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.
authors.affiliation: Centre for Ressources and Environmental Studies, Vietnam National University.
authors.forename: Tan Van
authors.initials: TV
authors.lastname: Dao
authors.forename: Mika
authors.initials: M
authors.lastname: Nomura
authors.forename: Rie
authors.initials: R
authors.lastname: Hamaguchi
authors.forename: Kensuke
authors.initials: K
authors.lastname: Kato
authors.forename: Manabu
authors.initials: M
authors.lastname: Itakura
authors.forename: Kiwamu
authors.initials: K
authors.lastname: Minamisawa
authors.forename: Suphawat
authors.initials: S
authors.lastname: Sinsuwongwat
authors.forename: Hoa Thi-Phuong
authors.initials: HT
authors.lastname: Le
authors.forename: Takakazu
authors.initials: T
authors.lastname: Kaneko
authors.forename: Satoshi
authors.initials: S
authors.lastname: Tabata
authors.forename: Shigeyuki
authors.initials: S
authors.lastname: Tajima