Negro jamapa were surface sterilized in 96% (v/v) ethanol for 30 s, followed by 5% sodium hypochlorite for 5 min and then thoroughly washed five times with sterilized water [41]. Sterilized seeds were incubated two hours in BIBW2992 manufacturer sterile distilled water in darkness. The imbibed seeds were deposited on plates containing 1% water-agar, and let them to germinate at 30°C during 60 h. Three day after sowing, selected uniform seedlings were planted in sterile 2-kg pots (4/pot) containing a mixture of vermiculite/sand (1:1 v/v) as substrate. Each seedling was inoculated

with 1 ml of the strains culture of R. etli wild-type and otsA mutant strain (CMS310) containing 108 cells/ml at the log-phase of growth. Plants were MLN2238 molecular weight grown in controlled environmental chambers (night/day temperature 19/25°C, photoperiod 16/8 h, PPF 400 μmol m-2

s-1 and relative humidity 60 to 70%) [49]. Plants were watered PLX4032 order with N-free mineral solution [50] and water alternately. When plants were three weeks old, they were randomly separated into two sets: control and drought stress. Drought stress was imposed by withholding water for 5 days (moderate drought) or for 10 days (severe drought). Control plants were supplied daily with nutrients solution to field capacity. Leaf water potential (Ψw) was measured in the first fully expanded leaf of common bean plants with C52 sample chambers connected to a HR-33 T psychrometer (Wescor. Inc., Logan UT, USA). Plant and nodule biomass, nitrogen content and nitrogen-fixation assays Plant and nodule dry weight were determined after drying fresh plant material that was heated at 60°C for 48 h. Total nitrogen content per plant was determined by the Kjeldahl method [51]. Nitrogenase activity was analyzed by using the acetylene reduction activity (ARA) assay. A Hewlett-Packard model 5890 gas chromatograph (Agilent Technologies, S.L., Madrid) equipped with a flame ionization detector was operated with a molecular sieve 5A (60 to Sitaxentan 80 mesh) column (180 × 0.32 cm). N2 at 60 ml min–1 served as a carrier gas. Oven, injector,

and detector temperatures were 60, 90, and 110°C, respectively. Nodules (0.3 g) were placed in 17-ml tubes that were filled with 10% acetylene. Gas samples (0.5 ml) were taken from the tubes for ethylene analyses after incubation for 10 and 20 min. Concentration of ethylene in each sample was calculated from standards of pure ethylene. Leghemoglobin content Leghemoglobin content was measured by fluorimetry as previously described by La Rue and Child [52]. Nodules (0.3 g) were ground with 4 ml Lb extraction buffer (Na2HPO4·2H2O 40 mM (pH 7.4); NaH2PO4·H2O 10 mM (pH 7.4); K3Fe (CN)6 0.02%; NaHCO3 0.1%) supplemented with 0.1 g polyvinylpolypirrolidone (PVPP). The homogenate was centrifuged at 12 000 rpm at 4°C for 20 min, to retain the supernatant.