Salicylic Acid Improves the Salt Tolerance Capacity of Saponaria officinalis by Modulating Its Photosynthetic Rate, Osmoprotectants, Antioxidant Levels, and Ion Homeostasis

Abstract

Salicylic acid (SA) plays an important role in regulating salt stress tolerance in plants. However, there are no studies on the effect of exogenous SA on Saponaria officinalis under salt stress. To study the effectiveness of SA on mitigating salt stress, S. officinalis were used in a pot experiment of salt stress simulated with an NaCl solution (100, 200, and 300 mmol L−1), while an SA solution (0, 0.2, 0.4, 0.6, 0.8, 1.0 mmol L−1) was sprayed on leaves. Under salt stress, spraying SA caused an increase in the salt damage index, electrolyte leakage, and a reduction in malondialdehyde and Na+ content, but an increase in the rate of photosynthesis, chlorophyll, soluble sugar, soluble protein, free proline, K+, Mg2+, Ca2+ content, the K+/Na+ ratio, superoxide dismutase, peroxidase, catalase, ascorbate peroxidase activity, and the comprehensive score. The results show that SA improves the salt tolerance capacity of S. officinalis by modulating its photosynthetic rate, osmoprotectants, antioxidant levels, and ion homeostasis. However, the effectiveness of SA was not linearly related to its concentration. In summary, our findings reveal the protective roles of SA against salinity in S. officinalis and suggest that the use of 0.6 mmol L−1 of SA in salt stress conditions could be an effective approach to reduce the damage caused by saline soil in S. officinalis.