Integrated physiological analysis reveals that recovery capacity after salt stress withdrawal is a crucial mechanism for salt tolerance in soybean cultivars

Although a great number of studies have focused on salt tolerance in cultivated plants, the physiological mechanisms involved in this process are still not completely understood. This study aimed to perform an integrated physiological analysis in two cultivars of soybean, M-Soy 8222 (salinity sensitive) and M9144 RR (salinity tolerant). Soybean plants were exposed to salinity for 7 or 14 days followed by recovery period of 7 days in greenhouse conditions. The sensitive cultivar showed higher contents of Na+ and Cl− in leaves than that of tolerant cultivar. In salt tolerant cultivar, Na+ and Cl− ions were greatly retained in roots. In parallel, the K+ content was reduced in roots of both cultivars but the leaf K/Na ratios fully recovered only in the tolerant cultivar after 7 days of salt stress withdrawal. The oxidative stress indicators were intensely increased especially in the sensitive cultivar and activities of the main antioxidant enzymes were not able to avoid ROS accumulation. In contrast, the tolerant cultivar showed a more efficient enzymatic antioxidant system represented by ascorbate peroxidase, catalase and superoxide dismutase avoiding oxidative damages. Interestingly, the sensitive cultivar displayed prominent increase in proline and glycinebetaine contents in parallel to strong reduction in photosynthetic pigment contents, indicating that these changes were more effects of metabolic disturbances than osmotic adjustment. Our data indicate that higher level of tolerance of M9144 RR cultivar is related to simultaneous triggering of several integrated physiological mechanisms involved in maintaining of ionic homeostasis, water status, photosynthetic pigments and oxidative protection.