Salt tolerance of Elaeagnus macrophylla and Frankia Ema1 strain isolated from the root nodules of E. macrophylla

Effects of NaCl on the seed germination and growth of Elaeagnus macrophylla seedlings and multiplication of Frankia Ema1 strain isolated from the root nodules of E. macrophylla were examined. The germination rate of seeds was not reduced by N aCI at 50 mM, but was reduced with further increase of the concentration, and germination did not occur at 200 mM NaCl. Root nodules were formed in the seedlings treated with 100 mM NaCl. The fresh and dry weight of the seedlings slightly decreased by the increase of the concentration of NaCl and the rate of decrease was 10–20% at NaCl concentrations higher than 100 mM. However, Na+ concentrations in the shoot increased up to 300 mM by treatment with N aCI at a concentration above 50 mM for 30 d and in some plants the lower leaves fell. The growth of free-living Frankia was markedly suppressed and the hyphae became thick and short in the solution at 100 mM NaCl. This trend was more obvious at 200 mM NaCl. Na⁺ concentration in the cells in the medium with 200 mM NaCl was lower than 20 mM and the cells underwent multiplication again when they were transferred to the medium which did not contain N aCl. These results indicate that the salt tolerance of E. macrophylla seedlings was not very high and the threshold for NaCl ranged between 50 and 100 mM, whereas Frankia Ema1 strain was able to survive in a much higher salt environment.