Importance of ferric chelate reductase activity and acidification capacity in root nodules of N-2-fixing common bean (Phaseolus vulgaris L.) subjected to iron deficiency

Iron is an essential nutrient for plants, especially in symbiotic N-2-fixing legumes. Although abundant in the soil, iron is generally not available to plants as it is predominantly in an insoluble form (Fe-III). Mono- and dicotyledonous plants, except Gramineae, have developed morphological and physiological responses, notably an increase in rhizosphere acidification (H+-ATPase) and an enhanced plasma membrane ferric chelate reductase activity (Fe-CR) in the roots. However, studies on the physiological responses of root nodules are lacking. The present study was initiated to investigate the acidification capacity and Fe-CR activity of nodulated roots, and intact nodules, in two contrasting common bean varieties, Coco blanc sensitive to iron deficiency and Flamingo tolerant to iron deficiency. The discovery of an induction of H+-ATPase and FeCR activities in root nodules of common bean under iron deficiency, suggests that these organs participate in improving iron availability for the contained bacteroids.