Silicon delays salt stress-induced senescence by increasing cytokinin synthesis in tomato

Silicon (Si) is beneficial for plant growth and development, and many studies have shown that Si can alleviate biotic and abiotic stress-induced plant damage. Although the alleviative effect of Si on plant damage induced by salt stress has been widely reported, the underlying mechanism is still not very clear. Here, the effect of Si on salt stress-induced leaf senescence and the role of cytokinin in this process were investigated. The results showed that added Si could significantly decrease chlorophyll degradation induced by salt treatment in tomato. Under salt stress, the effect of Si on the levels of indoleacetic acid and gibberellins in tomato was irregular and dependant on the Si treatment concentrations. Si addition increased the concentrations of cytokinins and abscicic acid, and the expressions of major cytokinin sysnthesis genes in leaf discs of tomato under salt stress. Cytokinin synthesis inhibitor abolished the ameliorative effect of Si on salt-induced leaf senescence of tomato. Si could alleviate salt-induced senescence in the leaves of wild type Arabidopsis thaliana but not in the ipt1,3,5,7 mutant, which has very little amount of cytokinin. These results suggest that Si can delay salt stress-induced plant senescence by increased cytokinin synthesis. This study may help us further explore the in planta mechanism for Si-mediated stress tolerance in plants.