Silicon Promotes Na⁺ Compartmentalization and Mineral Uptake in Zucchini Seedlings to Maintain Physiological Homeostasis and Alleviate Salt Stress

To investigate the effects of exogenous silicon on oxidative damage, hormone levels, and Na⁺ accumulation in zucchini seedlings under salt stress and provide theoretical references for the salt-tolerant cultivation of zucchini. The zucchini variety ‘Lvzun 8108’ was used as the experiment material. Four treatments were carried out using hydroponics test: control (CK), silicon treatment (0.3 mmol/L Na₂SiO₃·9H₂O), salt stress (150 mmol/L NaCl), salt stress + silicon treatment (150 mmol/L NaCl + 0.3 mmol/L Na₂SiO₃·9H₂O). After 10 d of treatment, the growth indexes, antioxidant indexes, endogenous hormones, Na⁺ content and distribution, expression of Na⁺ transport-related genes, and mineral ion content of zucchini seedlings were measured. Applying silicon could improve the growth of zucchini seedlings under salt stress, reduce oxidative damage, and increase the auxin, cytokinin, and gibberellin content in seedlings. The expression of Na⁺ transport-related genes SOS1 and NHX1 in leaves and roots of zucchini seedlings and HKT1 in leaves were promoted under salt stress, the Na⁺ content in chloroplasts was reduced, and the content of mineral elements such as Ca, Fe, Zn, K, Mg, Fe, and Mn in plants was increased. Silicon could maintain the antioxidant system activity of zucchini seedlings, regulate the level of endogenous hormones, upregulate the expression of Na⁺ transport genes, promote Na⁺ regionalization, reduce the accumulation of Na⁺ in chloroplasts, mitigate the toxic effects of Na⁺, thus alleviating the damage salt stress for zucchini seedlings.