Exogenous salicylic acid alleviates salt-stress damage in cucumber under moderate nitrogen conditions by controlling endogenous salicylic acid levels

Salicylic acid (SA) is a signaling compound that plays an important role in plant responses to biotic and abiotic stress. Exogenous application of SA can improve abiotic stress tolerance in various plants, a response that varies depending on the nutrient status of the plant. Based on the hypothesis that the nutrient status of a plant affects SA-induced stress tolerance, we investigated SA-induced stress tolerance in cucumber grown under moderate nitrogen (MN, 120 ppm) and low nitrogen (LN, 40 ppm) conditions. Cucumbers grown under MN conditions showed SA-induced tolerance to salt stress, along with mild increases in endogenous SA levels. In cucumbers without SA pretreatment, the increase in endogenous SA levels after salt stress treatment was approximately 2-fold higher than that of SA-pretreated plants. On the other hand, exogenous SA did not increase salt-stress tolerance in plants grown in LN exhibiting leaf chlorosis, although SA levels increased in the leaves of these plants. These results indicate that exogenous SA-induced salt stress tolerance is well established in cucumber grown in MN. In addition, SA pretreatment can improve the ability of plants to regulate endogenous SA levels after salt stress when grown under suitable nutrient conditions.