Keywords: 
• suboptimal condition /
• pesticide /
• phytotoxicity /
• gene transcription /
• stress tolerance

Abstract: Many pesticides probably have phytotoxicity on exposed plants. However, there is little available information regarding the stress response of crops to pesticides in the greenhouse under suboptimal condition with chilling temperature and low light. Brassinosteroids are one of new type of plant hormones, while their mitigation the toxicity of pesticide on crops under the suboptimal condition remain unclear. In this study, the transcriptional responses to chlorpyrifos in the leaves of cucumber (Cucumis sativus), was studied under the condition of the chilling temperature and low light in the artificial climate incubators. Cucumber was treated with chlorpyrifos at two concentrations (0.3and 1.0mmol·L^-1) and the leaves were sample after 1, 3and 7days of exposure. In order to reveal whether the brassinosteroid can alleviate the phytotoxicity, cucumber was pretreated with 24-epibrassinolide 24h before chlorpyrifos-exposure. The transcriptional level of genes involved in photosynthesis (psaB, psbA and rbcL), protection against oxidative stress (cAPX, DHAR, GR, CAT and GPX), defense (PAL, HPL and ADC) and heat shock (HSP70) were determined using quantitative real-time PCR. The results showed that chlorpyrifos treatment significantly reduced the transcriptional level for most genes under the condition of the chilling temperature and low light. While the transcriptions were induced after 24-epibrassinolide pretreatment, demonstrating that the brassinosteroid could protect crops against the phytotoxicity of pesticides effectively and persistently.