Nitric oxide, as a downstream signal, plays vital role in auxin induced cucumber tolerance to sodic alkaline stress

Nitric oxide (NO) and auxin (indole-3-acetic acid; IAA) play vital roles in regulating plants tolerance to abiotic stresses. This study showed that both NO and IAA could induce cucumber plants tolerance to sodic alkaline stress, which depended on their roles in regulating reactive oxygen species (ROS) scavenging, antioxidative enzymes activities, Na+ accumulation and protecting photosystems II (PSII) from damage. In addition, IAA has significant effect on NO accumulation in cucumber root, which could be responsible for IAA-induced sodic alkaline stress tolerance. Further investigation indicated that the function of IAA could be abolished by NO scavenger (cPTIO). On the contrary, IAA transport inhibitor (NPA) showed no significant effects on abolishing the function of NO. Based on these results, it could be concluded that NO is an essential downstream signal for IAA-induced cucumber tolerance to sodic alkaline stress.