Silicon can improve seed germination and ameliorate oxidative damage of bud seedlings in cucumber under salt stress

It has been extensively demonstrated that silicon has beneficial effects on plant growth and development under salt stress; whereas less attention has been paid to its effect on seed germination, and the underlying mechanism is also unknown. Here, we investigated the effect of silicon on seed germination and oxidative damage of bud seedlings in cucumber under salt stress. The results showed that, 0.3 mM silicon could increase seed germination percentage, germination index and seedling vigor index under 200 mM NaCl. Twelve hours after germination initiation, the expression of CYP707A1, which encodes ABA 8 '-hydroxylase, was increased by added silicon under salt stress; while the expressions of GA20ox, GA3ox and GA2ox, which encode genes involved in gibberellin metabolism, were not changed in seeds. Thirty-six hours after germination initiation, added silicon markedly inhibited the expressions of ABA biosynthesis genes (NCED1 and NCED2) and gibberellin catabolism gene GA2ox. The alpha-amylase activity was higher in silicon-applied seeds than the control under salt stress. Compared with salt stress alone, added silicon improved the growth and plasma membrane integrity of bud seedlings, while decreasing reactive oxygen species accumulation and lipid peroxidation. Added silicon decreased the activities of superoxide dismutase, catalase, peroxidase and ascorbate peroxidase, and the concentrations of protein and proline in radicles of bud seedlings under salt stress, implying a stress alleviation. These results suggest that silicon might decrease ABA level, maintain high gibberellin level and increase alpha-amylase activity, therefore improving cucumber seed germination under salt stress. The alleviation of oxidative damage by added silicon contributed to the improvement of bud seedling growth under salt stress.