Growth and nitrogen assimilation in nodules in response to nitrate levels in Vicia faba under salt stress

This study analyses the effects of salt on the effective symbiosis of faba bean (Vicia faba L, var. minor cv. Alborea) and salt-tolerant Rhizobium leguminosarum biovar. viciae strain GRA19 grown with two KNO3 levels (2 and 8 mM). The addition of 8 mM KNO3 to the growth medium increases plant tolerance to salinity even with a concentration of 100 mM NaCl. This KNO3 level in control plants reduced the N-2 fixation. For 2 and 8 mM KNO, the plants treated with NaCl reduced N-2 fixation to identical values. The activity of the enzymes mediating ammonium assimilation in nodules (GS, NADH-GOGAT and NADH-GDH) was decreased by high KNO, levels. The results show that NADH-GOGAT activity was more markedly inhibited than was GS activity by salinity, therefore NADH-GOGAT limits the ammonium assimilation by nodules in Ii. faba under salt stress. The total proline content in the nodule was not related to salt tolerance and thus does not serve as a salt-tolerance index for V. faba.