Isoflavone reductase is an enzyme involved in isoflavonoid biosynthesis in plants. However, rice isoflavone reductase-like gene (OsIRL, accession no. AY071920) has not been unraveled so far. Here, we have characterized its behavior in response to oxidizing agents. Using Northern and Western blot analyses, the OsIRL gene and protein were shown to be down-regulated in young seedling roots treated with reduced glutathione (GSH) and diphenyleneiodonium (DPI), known quenchers of reactive oxygen species (ROS). The OsIRL transcript level in rice suspension-cultured cells was also found to be induced by oxidants such as hydrogen peroxide (H(2)O(2)), ferric chloride (FeCl(3)), methyl viologen (MV) and glucose/glucose oxidase (G/GO), but down-regulated when co-treated with GSH. Furthermore, to investigate whether overexpression of OsIRL in transgenic rice plants promotes resistance to ROS, we generated transgenic rice lines overexpressing the OsIRL gene under an abscisic acid (ABA) inducible promoter. Results showed that the OsIRL transgenic rice line activated by ABA treatment was tolerant against MV and G/GO-induced stress in rice leave and suspension-cultured cells. Our results strongly suggest the involvement of OsIRL in homeostasis of ROS.