Hydrogen Gas Improves Seed Germination in Cucumber by Regulating Sugar and Starch Metabolisms

Hydrogen gas (H2), an important gaseous regulator, is involved in various plant growth and development processes. However, there have been few studies on the role of H2 in seed germination. In this study, the role and underlying mechanisms of H2 in enhancing seed germination were investigated in cucumber (Cucumis sativus L.). The results revealed that the germination rate, germ length, germination index, and vitality index of cucumber exhibited a dose-dependent relationship with the increase in concentrations of hydrogen-rich water (HRW, a H2 donor; 0, 1, 10, 25, 50, 75, and 100%), attaining the maximum values with 75% HRW treatment. Treatment with 75% HRW resulted in higher contents of soluble sugar, soluble protein, and starch than the control. Additionally, the activity of α-amylase, β-amylase, and total amylase was significantly improved by 75% HRW treatment compared to the control, reaching the maximum values at 36 h. Moreover, the expression levels of starch-related genes AMY and BMY and sugar-related genes SS4 and SS3 were significantly upregulated by 75% HRW treatment during germination, particularly at 36 h. These results suggest that H2 might promote cucumber seed germination by increasing sugar and starch metabolisms.