Horizon 1 1 17 ACLN : Articles dans des revues avec comité de lecture non répertoriées par l'AERES New Phytologist 571-578 LEGUMINEUSE TROPICALE FIXATION BIOLOGIQUE DE L'AZOTE MYCORHIZE METABOLISME ENZYME BESOIN EN EAU ETUDE COMPARATIVE NITRATE REDUCTASE GLUTAMINE SYNTHETASE ZONE ARIDE ZONE SEMIARIDE 2000 fdi:010025486 ENG New Phytologist 0028-646X 10.1046/j.1469-8137.2000.00714.x https://www.documentation.ird.fr/hor/fdi:010025486 https://horizon.documentation.ird.fr/exl-doc/pleins_textes/pleins_textes_7/b_fdi_57-58/010025486.pdf 147 Horizon (IRD) The activities of nitrate reductase and glutamine synthetase were evaluated in young plants of #Faidherbia albida$, a tropical woody legume, fed with different N sources under hydroponic conditions. Results showed that assimilation of both NO3- and NH4+ preferentially took place in shoots. A basal amount of nitrate reductase activity was detected in shoots of plants grown with an NO3- free solution or placed under N2-fixing conditions, and also in nodules of N2-fixing plants. This strongly suggests that constitutive nitrate reductase activity is present in these organs. Analyses of the soluble nitrogenous content showed that the major form of N in the different organs was alpha-amino acids (particularly amides), irrespective of the N status of the culture conditions. The same result was obtained for nodulated plants grown in local sandy soil. In this case, amide-N generally counted for more than 40% of the total soluble N. This was especially true in nodules. Ureide-N never exceeded 9% of the total soluble N and did not appear to increase with increasing nodule nitrogenase activity. Amides were also predominant in three N2-fixing Sahelian acacias (#Acacia seyal$, #A. nilotica$ and #A. tortilis$), showing that #F. albida$ does not differ from Sahelian #Acacia$ in terms of the metabolism of fixed N. However, like another Sahelian acacia growing preferentially near water (#A. nilotica$), #F. albida$ can be distinguished from acacias growing strictly in arid zones (#A. seyal$ and #A. tortilis$) in terms of initial growth, water and nitrate management. (Résumé d'auteur) 084SYMBIO02