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A greenhouse experiment was carried out aiming to study the effect of iron deficiency on nitrogen fixation and ammonium assimilation in common bean nodules. Host-plant and nodule growth, symbiotic nitrogen fixation, glutamine synthetase (GS) and glutamate dehydrogenase (GDH) were analyzed in two common bean varieties subjected to iron deficiency. Results showed that host-plant and nodules growth, nitrogen fixation and GS activity decreased when under Fe-deficiency against an important increase of ammonium accumulation and GDH activity. Tolerant variety Flamingo is clearly less affected by iron deficiency than the sensitive one, Coco blanc. The allocation of iron to nodules and Fe use-efficiency for nodule growth and symbiotic nitrogen fixation were on the basis of the symbiotic performance of Flamingo under iron deprivation. Under Fe-deficiency, GDH take over GS the ammonium assimilation activity, particularly in the tolerant variety. Keywords Common bean . Fe use-efficiency . Glutamate dehydrogenase . Glutamine synthetase . Symbiosis Abbreviation ARA acetylene reduction activity GDH glutamate dehydrogenase GOGAT glutamate synthase GS glutamine synthetase SNF symbiotic nitrogen fixation Plant Soil (2008) 312:49-57

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