We determined the 5'-flanking sequences of two nuclear genes (SodCc1 and SodCc2) encoding cytosolic copper/zinc-superoxide dismutase in rice (Oryza sativa L.). Utilizing transient beta-glucuronidase (GUS) reporter assays, functional promoter-GUS analysis was performed in rice protoplasts exposed to the phytohormone abscisic acid (ABA) or the antioxidant sulfhydryl reagent, dithiothreitol (DTT). Transcriptional activities from both SodCc-GUS fusions were stimulated by DTT, which induces the promoter activity of the tobacco SodCc gene [Proc. Natl. Acad. Sci. USA 90 (1993) 3108-3112]. ABA had no effect on SodCcl-GUS expression but specifically induced the gene expression of the SodCc2-GUS fusion. The simultaneous application of ABA and gibberellin A3, however, abolished the enhancing effect of ABA. These results indicated that two rice SodCc promoters differentially respond to externally supplied ABA and that one of the regulatory factors for plant SodCc expression is ABA in addition to cellular redox-modulating antioxidants.