Catalase gene expression in response to auxin-mediated developmental signals.

The effect of auxin on maize catalase gene expression was examined at several different developmental stages during embryo and seedling development. All three catalase genes and their respective proteins were induced by both natural and synthetic auxin in immature embryos. Total catalase (CAT) activity increased dramatically in response to high concentrations of auxin, with CAT-2, which is not normally expressed at this stage, being the isozyme most responsible for the increase. Cat1 transcript accumulated to high levels at 2-8 h after auxin treatment, while Cat2 and Cat3 transcripts increased dramatically, but only after 12 h. In CAT-2 null mutant lines, the CAT-1 isozyme compensated for the missing CAT-2 activity and was the major isozyme responsible for the observed increase in total CAT activity. Auxin treatment mimics the germination process (i.e. induces germination) in immature embryos. Thus, the observed early induction of CAT-1 and the later increase of CAT-2 during the germination process may be due, in part, to changes in auxin content. In germinating embryos, auxin also induces total CAT activity and Cat transcript accumulation, although to a lesser extent. Auxin also induces Cat1 transcript accumulation in young leaves. The involvement of ROS in the auxin response is discussed.