Abstract: This experiment was conducted to determine the mechanism involved in silicon mitigation of osmotic stress in cucumber（Cucumis sativus L.‘Xinchun 4’）seed germination and seedling growth.Four treatments including distilled water（Control），silicon treatment（Si），PEG-6000 simulated drought stress（PEG）and PEG-6000 + Silicon（PEG + Si）were applied. The results showed that compared with the control，10% PEG treatment significantly inhibited germination，seedling vigor，seedling length and fresh weight. Moreover，the contents of malondialdehyde（MDA），free proline（Pro）content and the activities of antioxidant enzymes increased under the sole PEG treatment. However，PEG + Si treatment significantly alleviated the osmotic stress in the cucumber seedlings. The PEG + Si treatment enhanced germination，increased seedling vigor，seedling length and fresh weight. Moreover，the activities of antioxidant enzymes of shoots were significantly greater than those of PEG treatment whiles the contents of MDA and Pro were significantly lower compared to the PEG treatment. The effect of sole Si treatment on germination，seedling vigor，seedling length，fresh weight，MDA content，Pro content and antioxidant enzyme activities was not significantly different from the control treatment. During cucumber seed germination，PEG treatment increased starch content but decreased the content of soluble sugar by down-regulating the Amylase（AMY）and β-amylase（BMY）gene expression levels at 36 h. However，the PEG + Si treatment significantly reduced starch content，increased soluble sugar content，α-amylase activity and β-amylase activity，and significantly up-regulated the expression levels of AMY and BMY genes at 36 h after treatment. The changes in starch content，soluble sugar content，α-amylase activity and β-amylase activity in the Si treated seedlings was not statistically different from the control seedlings. However，Si treatment significantly up-regulated BMY gene expression but did not affect the expression of AMY. It can be concluded that Si might alleviate the lipid peroxidation damage of cucumber seeds and accelerate the conversion of carbohydrates under drought stress by increasing the antioxidant enzyme activities，starch hydrolase activity，reducing MDA accumulation，and up-regulating the AMY and BMY gene expression levels for promoting the germination of cucumber seeds.

Key words: cucumber, silicon, osmotic stress, seed germination, antioxidase activity, amylase activity