This study was conducted to evaluate the role of ethylene in acute ozone (O₃: 0, 0.1, and 0.3 cm³ m^–3; O⁰, O^0.1 and O^0.3, respectively)-induced photosynthetic inhibition of paddy rice leaves grown under different atmospheric carbon dioxide concentrations (CO₂: 400 and 800 cm³ m^–3; C⁴⁰⁰ and C⁸⁰⁰, respectively). Ethephon and silver thiosulfate complex (STS) were applied one day before exposure to O₃. Gas exchange, chlorophyll fluorescence, and ascorbic acid were measured immediately before (BE), immediately after (AE-0), and 1 d and 3 d after (AE-1, AE-3) the start of the exposure to O₃. In the plants exposed to O₃, visible leaf symptoms on the adaxial leaf surface appeared at AE-3. O₃ decreased photosynthesis-related parameters, total ascorbic acid content, and redox state of ascorbic acid (RDS), and C⁸⁰⁰ ameliorated O₃-induced damage. STS ameliorated the O₃-induced visible leaf symptoms and O₃-inhibition of photosynthesis but ethephon worsened slightly or did not affect them. Additionally, we evaluated the effects of O₃ and CO₂ on ethylene production in rice leaves. Although elevated CO₂ did not affect ethylene production, exposure to O₃ greatly increased ethylene production at AE-0 and rapidly reduced it at AE-1. These results indicate that ethylene is an important component of signal transduction for the extension of O₃ injury in paddy rice.

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