Ammonium assimilation and ureide metabolism in common bean (Phaseolus vulgaris) nodules under salt stress

摘要

The effect of salinity on ammonium-assimilation enzymes, as well as on the enzymes of purine catabolism, was studied in root nodules of common bean plants grown in an environmentally controlled chamber. Salt treatments (0, 25, 50 and 100 mM) were applied during the vegetative period, when the symbiosis was well established. Four harvests were made, two during the vegetative and two during the reproductive period. Salinity reduced plant dry weight by 25% with salt high levels in the third and fourth harvests. Also, nitrogenase activity was reduced by the highest levels of salinity in the last two harvests, as well as glutamine synthetase and glutamate synthase. Xanthine dehydrogenase and uricase activities showed a pattern closely related to those of total nitrogen per plant. The total N content of the plants revealed no significant reduction. We reported that the inhibition of enzymatic activities related to ammonium assimilation of the GS/GOGAT pathway promote other enzyme activities (GDH and AAT). The inhibition of enzymes related to purine catabolism (xanthine dehydrogenase and uricase) decreased the ureide content and alternatively the amino acid content increase in the nodules of common bean.