Hydrogen peroxide-mediated catalase gene expression in response to wounding

The effect of wounding on catalase expression was examined in embryos and l eaves of maize. All three Cat genes are upregulated in response to wounding in immature embryos. Cat expression also increased in response to jasmonic acid (JA), raising the possibility that JA and wounding may share a common signal transduction pathway in upregulating Cat mRNA in immature embryos. In young leaves, only Cat1 and Cat3 transcripts increase in response to wou nding, but JA does not play a role. Cat1 and Cad transcript accumulation al so increases in response to wounding in both wild-type and mutant leaves de ficient in abscisic acid (ABA), implying that Cat1 and Cat3 induction in re sponse to wounding is not mediated by ABA in leaves. Transient assays using the Cat1 promoter fused with the reporter gene Gus, showed that the DNA se quence motif responsible for Cat1 upregulation by wounding overlaps with th e ABA-responsive element (ABRE, G-box) in the Cat1 promoter. The exact natu re of the signals triggering the Cat responses to wounding is not clear at this point, but some evidence indicates that reactive oxygen species (ROS) play a role in this response. In fact, we have found that endogenous H2O2 l evels increase in wounded leaves. Thus, wounding may indirectly induce the production of H2O2 in leaves, triggering the antioxidant response. (C) 2000 Elsevier Science Inc.