Abstract: The purpose of this paper is to investigate the regulation mechanism of exogenous hydrogen sulfide（H2S）on chilling tolerance in cucumber（Cucumis sativa L.）plants.‘Jinyou 3’cucumber plants were used as materials. The respond of H2S to temperature and the effect of sodium hydrosulfide（NaHS，the donor of H2S）on photosynthesis and antioxidant system in cucumber were investigated，with distilled water as the control. The results showed that H2S content and D-/L-cysteine desulfhydrase（CDes）activity increased at first and then decreased as the temperature decreased and lasted. Low temperature led to decrease in photosynthetic rate（Pn），stomatal conductance（Gs），transpiration rate（Tr），ribulose bisphosphate carboxylic enzyme（RuBPCase）activity，maximum photochemical efficiency of PSⅡ in darkness（Fv/Fm），actual photochemical efficiency of PSII（ΦPSII），electron transport rate（ETR）and photochemical quenching（qP），while increase in intercellular CO2 concentration（Ci），initial fluorescence（Fo）and non-photochemical quenching（NPQ）. Low temperature increased malondialdehyde （MDA）content. The superoxide dismutase （SOD），peroxidase（POD），catalase （CAT），ascorbate peroxidase（APX）and glutathione reductase（GR）activities increased in the early days of chilling stress，but subsequently decreased. Compared with the control，the NaHS treated leaves showed significantly higher H2S content，CDes activity，Pn，Gs，Tr，RuBPCase activity，Fv/Fm，ΦPSII，ETR and qP，whereas markedly lower Ci，Fo and NPQ. NaHS caused a significant decrease in MDA content，but an increase in SOD，POD，CAT，APX and GR activities. The yield of NaHS-treated cucumber plants was 15.3% higher than that of the control. This indicated that H2S which is catalyzed by CDes was induced by chilling stress. Exogenous H2S can enhance the ROS scavenging activity，and alleviate the injury of photosynthetic apparatus in cucumber leaves against low temperature.

Key words: cucumber, chilling stress, reactive oxygen（ROS）, photosynthesis, hydrogen sulfide （H2S）