The investigation of the role of NPR1-dependent salicylic acid with increasing salinity tolerance in accumulated soybean leaves

Non-expressor of Pathogen Related 1 (NPR1) is a regulatory gene of the salicylic acid (SA) signaling pathway, the detailed mechanism of which is still not well understood. This study investigated the effects of NPR1-dependent SA level change on increasing salt tolerance of soybean leaves with acclimation. Salt-sensitive ('SA88') and salt-tolerant ('Erensoy') soybean (Glycine max L.) plants were treated with increasing NaCl concentrations (25, 50, 75 and 100 mM; acclimation) and with 100 mM NaCl directly (non-acclimation) in two groups. The results showed that acclimation treatment alleviated salt induced damage in the sensitive cultivar with increasing superoxide anion radical scavenging activity and decreasing hydrogen peroxide (H2O2) and malondialdehyde (MDA) content. However, the APX, CAT, and GST enzyme activities were increased by acclimation treatment, with the highest increase observed in GST enzymes. Interestingly, the Gmnpr1 gene expression was upregulated in all treatments but was more pronounced in non-acclimation. Furthermore, endogenous SA level was increase under acclimation treatment in 'SA88'. In conclusion, the results firstly showed that an acclimation process is useful for increasing salt tolerance in sensitive soybean plants with only ROS-induced NPR1-independent SA accumulation but not through the NPR1-dependent SA signaling pathway.