The response to the osmotic effects of drought may largely vary not only between species but even cultivars of the same species. Gaining knowledge of the reasons underlying these differential responses can be critical in breeding programs to obtain lines with enhanced performance under drought or salinity. In this work, the responses to osmotic stress of two common bean (Phaseolus vulgaris L.) cultivars with contrasting tolerance (Coco blanc, sensitive, and Flamingo, tolerant) have been assessed by analyzing a full array of nodule parameters (enzyme activities, carbohydrate and organic acids content and antioxidant activity). The aim of this work was to study the likely involvement of carbon flux shortage in the decline of N2 fixation under osmotic stress. The maintenance of sucrolytic activities, particularly sucrose synthase, to keep an adequate glycolytic flux, together with isocitrate dehydrogenase, to balance C/N interactions, associated with a suitable antioxidant defense may be relevant for osmotic tolerance in common bean nitrogen fixation.
