Calcium-induced salt tolerance inRhizobium leguminosarumbiovarviciaestrain C124b

CaCl2 can induce NaCl tolerance in the free-living microsymbiont Rhizobium leguminosarum biovar viciae. The phenomenon of external Ca2+ alleviating salt stress has been previously reported for the freshwater alga Nitellopsis obtusa as well as for higher plants. The divalent cations, St2+, Ba2+, and Mg2+ were able to substitute in part for the CA2+-mediated effect. Substitution of sucrose for NaCl to the same osmolality did not result in growth arrest, suggesting that Ca2+ was not conferring an osmotic alleviation. Tn5-induced mutants of R. leguminosarum biovar viciae strain C1204b were isolated which no longer responded to the addition of exogeneous divalent cations in the alleviation of NaCl toxicity. All of the mutants but one maintained the same level of NaCl sensitivity as the parental strain. All of the mutants were Nod+ Fix+ on Pisum sativum.