Abstract：In order to verify the different response of cucumber scion and rootstock seed germination to autotoxic stress，and its potential physiological metabolism and gene regulation mechanism，this paper took cucumber and Cucurbita ficifolia as test material；set 0.25 mmol · L-1 exogenous cinnamic acid（CA）to simulate antotoxic stress；used distilled water as the contrast；and studied the effects of cinnamic acid on seed germination，radicle morphology，reactive oxygen species（ROS）accumulation and antioxidant system of cucumber and C. ficifolia．The results showed that CA treatment significantly inhibited the seed germination and radicle growth of cucumber. Its germination rate，radicle total root length，root surface area，root volume and number of root tips were decreased by 7.8 percent point，and 28.1%，22.2%，14.9% and 46.6%，respectively，than those of the contrast．While，the seed germination rate of C. ficifolia was slightly increased. Only root surface area was decreased by 17.2%．CA treatment had significantly promoted the accumulation of hydrogen peroxide（H2O2）and superoxide anion（O2-.）of cucumber during various germination period．At 48 h after germination，MDA content had increased significantly by 26.2% than that of the contrast．But，except for the significant accumulation of H2O2 in the later period of germination（48 h and 72 h）of C.ficifolia，there was no significant differences in the other indexes comparing with those of the contrast．CA treatment had caused increasing at first then decreasing in cucumber SOD，CAT，APX and GR activity. At 48 h after germination，those index reduced by 26.0%，33.3%，65.2% and 26.7%，respectively comparing with that of the contrast．However，the enzyme activity of C. ficifolia was always higher than or close to that of the contrast．The expression quantities of cucumber antioxidant enzyme genes Cu-ZnSOD，Fe-MnSOD，CAT，APX and GR under CA treatment were down-regulated by 95%，73%，70%，91% and 89%，respectively．While the five genes of C. ficifolia were up-regulated by 148%，272%，148%，199% and 272%，respectively．Therefore，the seed germination tolerance of C. ficifolia to cinnamic acid stress was higher than that of cucumber．The higher tolerance might depend on its well developed root system and stronger antioxidant capacity．
