Physiological and transcriptional responses to salt stress in salt-tolerant and salt-sensitive soybean (Glycine max [L.] Merr.) seedlings

Excess salinity is a major environmental threat to agriculture. However, the adaptive mechanisms underlying salt tolerance in soybean (Glycine max [L.] Merr.) remain unclear. The aim of this study was to investigate the differences between salt-tolerant and salt-sensitive soybeans in their physiological characteristics and the expression patterns of 8 cation antiporters under salt stress. The inhibitory effects of salt stress on growth and photosynthesis in salt-sensitive soybean were stronger than those in salt-tolerant soybean. The concentration of phosphate and most other ions in the seedlings significantly declined under a 150-mM-NaCl treatment. Relative K+, Mg2+, and P concentrations were significantly positively correlated with relative net photosynthetic rate. GmNHX1 (Glyma.10G158700) and GmNcl1 (Glyma.03g171500) had similar expression patterns in the salt-tolerant and salt-sensitive cultivars. Furthermore, a significant correlation was present between the transcript levels of these 2 genes and the Na+ concentration in soybean leaves. In addition to GmSALT3, which is the major gene in soybean for salt tolerance in previous studies, GmNHX1 and GmNcl1 may be associated with salt tolerance in soybean to some extent. The salt-tolerant cultivars in this study maintained higher K+, Mg2+, and P concentrations in the leaf and had higher photosynthetic rates than the salt-sensitive cultivar did under salt stress. These findings can provide theoretical references for the molecular breeding of salt-tolerant soybean and the sustainable use of saline soils.