Carbon dioxide enrichment and brassinosteroid pretreatment alleviate chlorpyrifos phytotoxicity under suboptimal light and temperature conditions in tomato

• Phytotoxicity of chlorpyrifos was evaluated mainly by transcriptional responses.
• Target genes were related to photosynthesis, oxidation, detoxification and defense.
• Phytotoxicity of chlorpyrifos was evident under chilling temperature and low light.
• Both EBR pretreatment and CO2 enrichment could mitigate chlorpyrifos phytotoxicity.

Phytotoxicity is a daunting challenge for facility agriculture, and a crop is more susceptible to phytotoxicity under sub-optimum growth conditions. Although the practical values of brassinosteroid (BR) treatment or CO2 enrichment in promoting crop yield have been confirmed, few studies have focused on the regulation of pesticide phytotoxicity, especially under sub-optimum growth conditions. In this study, the phytotoxicity of chlorpyrifos was evaluated mainly by monitoring the transcriptional responses of genes involved in various physiological processes in tomato leaves under chilling temperature and low light, which occur frequently during the cool season in China. Additionally, we investigated whether 24-epibrassinolide (EBR) pretreatment (0.1 μmol/L) or CO2 enrichment (1000 μmol/mol) could mitigate this phytotoxicity. The treatment of chlorpyrifos decreased the transcriptions of photosynthetic and defense genes and increased those of antioxidant and detoxification genes. EBR pretreatment significantly increased the transcription of antioxidant, detoxification and defense genes, which could enhance the tolerance of the plants to pesticides and mitigate the phytotoxicity, as indicated by the increased mRNA level for photosynthetic genes. Similar observations were found with CO2 enrichment, and the effects of CO2 enrichment were even more pronounced than the effects of EBR pretreatment for the photosynthetic genes. Moreover, the changes of antioxidant enzymes activity and lipid peroxidation further confirmed that the chlorpyrifos exposure induced the oxidative stress, which could be ameliorated by either EBR pretreatment or CO2 enrichment. These results strongly suggest a promising prospect for the practical application of BRs or CO2 enrichment to alleviate the phytotoxicity of pesticides in facility agriculture.

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