Nitrate reductase activity of free-living and symbiotic uptake hydrogenase-positive and uptake hydrogenase-negative strains ofBradyrhizobium japonicum

✍ Scribed by María J. Delgado; José Olivares; Eulogio J. Bedmar

• Publisher: Springer
• Year: 1989
• Tongue: English
• Weight: 558 KB
• Volume: 151
• Category: Article
• ISSN: 0302-8933
• DOI: 10.1007/bf00414433

✦ Synopsis

The nitrate reductase activity (NR) of selected uptake hydrogenase-positive (hup +) and uptake hydrogenase-negative (hup-) strains of Bradyrhizobium japonieum were examined both in free-living cells and in symbioses with Glycine max L. (Merr.) cv. Williams. Bacteria were cultured in a defined medium containing either 10 mM glutamate or nitrate as the sole nitrogen source. Nodules and bacteroids were isolated from plants that were only Nz-dependent or grown in the presence of 2 mM KNO3. Rates of activity in nodules were determined by an in vivo assay, and those of cultured cells and bacteroids were assayed after permeabilization of the cells with alkyltrimethyl ammonium bromide. All seven strains examined expressed NR activity as free-living cells and as symbiotic forms, regardless of the hup genotype of the strain used for inoculation. Although the presence of nitrate increased nitrate reduction by cultures cells and nodules, no differences in NR activity were observed between bacteroids isolated from nodules of plants fed with nitrate or grown on Nz-fixation exclusively. Cultured cells, nodules and bacteroids of strains with hupgenotype (USDA 138, L-236, 3.15B3 and PJ17) had higher rates of NR activity than those with hup + genotype (USDA 110, USDA 122 DES and CB1003). These results suggest that NR activity is reduced in the presence of a genetic determinant associated with the hup region of B. japonicum.