Abstract: In order to verify the interaction between hydrogen sulfide（H2S）and abscisic acid（ABA）in improving chilling tolerance of plants，we evaluated the effect of H2S and ABA on the reactive oxygen （ROS）accumulation and antioxidant system of cucumber（Cucumis sativa L.）seedlings subjected to chilling stress，that were pretreated with 1.0 mmol · L-1 sodium hydrosulfide（NaHS，H2S donor），0.15 mmol · L-1 hypotaurine（HT，H2S scavenger），50 μmol · L-1 ABA，3 mmol · L-1 sodium tungstate（Na2WO4，ABA inhibitor），3 mmol · L-1 Na2WO4 + 1.0 mmol · L-1 NaHS，0.15 mmol · L-1 HT + 50 μmol · L-1 ABA or deionized water（H2O）and the H2O pretreatment at room temperature was used as the control. The results showed that the cold injury index of NaHS- and ABA-pretreated seedlings decreased significantly after 48 h of chilling stress. ABA led to an increase in the activity and relative mRNA expression of L-/D-cysteine desulfhydrase（LCD/DCD），and consequently promoted the accumulation of endogenous H2S. Similarly，NaHS enhanced the 9-cis-epoxycarotenoid dioxygenase（NCED）activity and relative mRNA expression，and improved the endogenous ABA. NaHS and ABA reduced the accumulation of hydrogen peroxide（H2O2）and production rate of superoxide anion caused by chilling stress，whereas elevated the activities and relative mRNA expression of superoxide dismutase（SOD），peroxidase（POD），ascorbate peroxidase（APX）and glutathione reductase（GR），compared with the H2O-treated seedlings. Furthermore，NaHS and ABA led to an increase in the contents of ascorbic acid（AsA）and glutathione（GSH），as well as the ratio of reduced/oxidized ascorbic acid（AsA/DHA）and reduced/oxidized glutathione（GSH/GSSG）in stressed seedlings，thus resulting in the alleviation of oxidative damage. The H2S-induced positive effect on the antioxidant ability was weakened by addition of Na2WO4，a specific inhibitor of ABA biosynthesis. Similarly，the regulating role of ABA in the ROS metabolism in cucumber seedlings was also reversed by HT，a specific scavenger of H2S. All of the above-mentioned results suggest that H2S and ABA could improve the chilling tolerance of cucumber seedlings，and the two signal molecules have interaction and cross talk in the signal transduction.

Key words: cucumber, hydrogen sulfide, abscisic acid, reactive oxygen（ROS）, antioxidant system, low temperature