Salicylic acid negatively affects the response to salt stress in pea plants

Abstract

We studied the effect of salicylic acid treatments on the response of pea plants to salinity. The NaCl-induced damage in leaves increased by salicylic acid: this response correlated with a reduction in plant growth. The contents of reduced ascorbate and glutathione in leaves of salt-treated plants increased by effect of salicylic acid, although an accumulation of the respective oxidised forms occurred. An increase in hydrogen peroxyde also occurred in the leaves of salt-exposed plants which were treated by salicylic acid. In the absence of NaCl, salicylic acid increased the ascorbate peroxidase (100 µM) and glutathione-S transferase (50 µM) activities and increased catalase activity in a concentration-dependent manner. Salinity decreased glutathione reductase activity, but increased glutathione-S transferase and catalase activities. In salt-stressed plants, salicylic acid also produced changes in antioxidative enzymes: 100 µM decreased ascorbate peroxidase but increased glutathione-S transferase. Finally, a concentration-dependent increase in superoxide dismutase activity was induced by salicylic acid treatments in salt-stressed plants. An induction of PR-1b was observed in NaCl-stressed plants treated with salicylic acid. The treatment with salicylic acid, as well as the interaction between the salinity and salicylic acid treatments, had a significant effect on PsMAPK3 expression. The expression of PsMAPK3 was not altered by 70 mM NaCl, but it was statistically higher in the absence than in the presence of salicylic acid. Globally, the results show that salicylic acid treatments affected negatively the response of pea plants to NaCl, and this response correlated with an imbalance in antioxidative metabolism. The data also show that salicylic acid treatment could enhance the resistance of salt-stressed plants to a possible opportunistic pathogen attack, as suggested by increased PR-1b gene expression.