Silicon enhances root potassium retention in cucumber under salt stress through promoting sodium exclusion and antioxidant capacity

Salt stress induces potassium (K⁺) leakage and deficiency, thereby limiting plant growth. The decrement of K⁺ leakage (also called K⁺ retention) plays a key role in plant salt tolerance. Silicon (Si) can alleviate salt stress and promote K⁺ nutrition status in plants, however the mechanisms behind remain unclear. In this study, the regulatory effects and related mechanisms of Si on root K⁺ retention in cucumber were investigated. The results showed that salt stress induced significant growth inhibition, Na⁺ accumulation and K⁺ deficiency in cucumber, while Si decreased Na⁺ content and promoted K⁺ content, thereby promoting Na⁺/K⁺ homeostasis and cucumber growth under salt stress. Moreover, Si ameliorated the K⁺ leakage induced by both salt and simulated oxidative stress, which was further confirmed by the results of selective ion electrolyte technique (SIET). Meanwhile, Si enhanced antioxidant enzyme activity, total antioxidant capacity, and the expression of genes related to antioxidant system in cucumber root under salt stress. In addition, Si treatment enhanced root Na⁺ exclusion under salt stress, which could be based on the upregulated expression of SOS and NHX genes. Overall, our results show that Si can enhance root K⁺ retention in cucumber by promoting root Na⁺ exclusion and antioxidant capacity, thereby alleviating salt stress.