Silicon Nanoparticles Improve Tomato Seed Germination More Effectively than Conventional Silicon under Salt Stress via Regulating Antioxidant System and Hormone Metabolism

Salt stress is one of the major environmental problems in agricultural production, severely limiting crops' germination, growth and yield. Silicon (Si) is a widely recognized beneficial element in plants, which can promote plant growth especially under stressful conditions. With the emergence of nanotechnology in agriculture, silicon nanoparticles (SiNPs) have been shown to be a promising tool in nano-enabled agricultural production. However, the comparative effects of Si and SiNPs in alleviating salt stress in plants remain unclear, which would limit the application of SiNPs in agricultural practice. In this study, the effects of SiNPs and conventional Si (silicate) on tomato (a typical low-Si accumulator) seed germination, reactive oxygen species (ROS) content, antioxidant enzyme activity, and the expression of genes related to hormone metabolism were investigated. The results showed that SiNPs more effectively promoted seed germination percentage, fresh weight, and Si content than conventional Si. Simultaneously, SiNPs more significantly modulated the activities of antioxidant enzymes and alleviated salt stress-induced oxidative damage in tomato seeds. Moreover, exogenous SiNPs addition promoted the expression of genes responsible for gibberellin (GA) synthesis and abscisic acid (ABA) catabolism, while downregulating the expression of genes related to GA deactivation and ABA synthesis in tomato seeds under salt stress. Overall, our results indicate that SiNPs are more effective than conventional Si in promoting tomato seed germination under salt stress via modulating antioxidant enzyme activity and key endogenous hormone metabolism, which could be based on the higher accumulation of SiNPs in tomato seeds than conventional Si.