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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Calcareous soils are known problematic lands for agricultural systems because of the low availability of nutrients, particularly iron (Fe). The so-called strategy I plant (e. g. Pea, Pisum sativum L.) which groups dicotyledons and monocots other than grasses, developed root membrane activities that contribute to the improvement of Fe availability. Among the functions considered to be a critical phase in iron absorption is rhizosphere acidification by H-ATPase and Fe(III) reduced by Fe(III) chelate reducctase (FeCR). In order to experimentally investigate the importance of root FeCR in Fe nutrition, its relationship with rhizosphere acidification and the genotypic differences in response to iron deficiency in pea (Pisum sativum L.), a glasshouse experiment was conducted hydroponically on four genotypes Merveille de Kelvedon (MK); Lincoln (Lin); Douce de Provence (DP) and Alexandra (Alex). Plants of each genotype were distributed into two plots, the first one received full nutrient solution (+ Fe), the second one received nutrient solution devoid of iron (- Fe). Plant growth, Fe distribution, SPAD index and root acidification and ferric chelate reductase activities were evaluated. Fe deficiency decreased plant growth and SPAD index along with the significant increase of H-ATPase and FeCR activities. Some genotypic differences were observed as follows; Alex showed high tolerance to Fe deprivation as compared to other genotypes. Important H-ATPase and FeCR activities, high Fe use efficiency and adequate membrane efficiency are the main reasons for this tolerance. These physiological parameters could be used as tools of tolerance for further breeding programs

Five dry bean cultivars (Coco blanc, Striker, ARA14, SVM29-21, and BAT477) were evaluated for their resistance to iron deficiency on the basis of chlorosis symptoms, plant growth, capacity to acidify the external medium and the root-associated Fe 3þ -reduction activity. Plants were grown in nutrient solution supplied or not with iron, 45 mM Fe(III)EDTA. For all cultivars, plants subjected to iron starvation exhibited Fe-chlorosis. These symptoms were more severe and more precocious in BAT477 and Coco blanc than in the others cultivars. An important acidification of the culture medium was observed between the 4th and the 8th days of iron starvation in Striker, SVM29-21 and, particularly, ARA14 plants. However, all Fe-sufficient plants increased the nutrient solution pH. This