Differential Cl-/Salt Tolerance and NaCl-Induced Alternations of Tissue and Cellular Ion Fluxes in Glycine max, Glycine soja and their Hybrid Seedlings

The salt-sensitive Glycine max N23674 cultivar, the salt-born Glycine soja BB52 population, and their hybrid 4076 strain (F-5) selected for salt tolerance generation by generation were used as the experimental materials in this study. First, the effects of NaCl stress on seed germination, tissue damage, and time-course ionic absorption and transportation were compared. When qualitatively compared with seed germination appearance in culture dishes, and tissue damages on roots or leaves of seedlings, or quantitatively compared with the relative salt injury rate, the inhibition on N23674 was all the most remarkable. After the exposure of 140 mm NaCl for 1 h, 4 h, 8 h, 12 h, 2 days and 4 days, the content of Cl- gradually increased in the roots and leaves of seedlings of BB52, 4076 and 23674. Interestingly, the extents of the Cl- rise in roots of the three experimental soybean materials were BB52 > 4076 > N23674, whereas those in leaves were just on the contrary. Secondly, by using the scanning ion-selective electrode technique (SIET), fluxes of Na+ and Cl- in roots and protoplasts isolated from roots and leaves were also investigated among the three experimental soybean materials. After 140 mm NaCl stress for 2, 4 and 6 days, and when compared with N23674, slighter net Cl- influxes were observed in root tissue and protoplasts of roots and leaves of BB52 and 4076 seedlings, especially at the cellular protoplast level. The results indicate that with regard to the ionic effect of NaCl stress, Cl- was the main determinant salt ion for salt tolerance in G. soja, G. max and their hybrid, and the difference in their Cl-/salt tolerance is mainly attributed to the capacity of Cl- restriction to the plant above-ground parts such as leaves.