Nitrogen Assimilation In Nodules Research Articles

RNA interference-mediated repression of S6 kinase 1 impairs root nodule development in soybean.

Symbiotic nodule formation on legume roots is characterized with a series of developmental reprograming in root tissues, including extensive proliferation of cortical cells. We examined a possible involvement of the target of rapamycin (TOR) pathway, a central regulator of cell growth and proliferation in animals and yeasts, during soybean nodule development. Our results show that transcription of both GmTOR and its key downstream effector, GmS6K1, are activated during nodulation, which is paralleled with higher kinase activities of these gene products as well. RNAi-mediated knockdown of GmS6K1 impaired the nodule development with severely reduced nodule weight and numbers. In addition, expression of a few nodulins including leghemoglobin was also decreased, and consequently nitrogen fixation was found to be reduced by half. Proteomic analysis of the GmS6K1-RNAi nodules identified glutamine synthetase (GS), an essential enzyme for nitrogen assimilation in nodules, as one of the proteins that are significantly down regulated. These results appear to provide solid evidence for a functional link between GmS6K1 and nodule development.

Effect of salinity on growth, nodulation and nitrogen assimilation in nodules of faba bean ( Vicia faba L.)

A commercial cultivar (Alborea) of faba bean ( Vicia faba L. var. minor) was inoculated with salt-tolerant Rhizobium leguminosarum biovar. viciae strain GRA19 in solution culture with different salt concentrations (0, 50, 75 and 100 mmoles l −1 NaCl) added immediately at the time of inoculation. The results indicated that Rhizobium leguminosarum strain GRA19 formed an infective and effective symbiosis with faba bean under saline and nonsaline conditions. Salinity significantly decreased shoot and root dry weight, nodule weight and mean nodule weight. Roots were more sensitive than shoots, and N 2 fixation was more sensitive to salinity than was plant growth. Analyses of ammonium assimilating enzymes in the nodule showed that glutamine synthetase appeared to be more tolerant to salinity than glutamate synthase, and that it limits ammonium assimilation under saline stress.

Growth and nitrogen assimilation in nodules in response to nitrate levels inVicia fabaunder 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 KNO 3 levels (2 and 8 mM). The addition of 8 mM KNO 3 to the growth medium increases plant tolerance to salinity even with a concentration of 100 mM NaCl. This KNO 3 level in control plants reduced the N 2 fixation. For 2 and 8 mM KNO 3 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 3 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 V. faba under salt stress. The total proline content in the nodule was not related to salt tolerance and thus does not serve as a salttolerance index for V. faba.