The effects of abscisic acid (ABA) and high osmoticum on catalase ( Cat ) gene expression in maize have been examined. Each Cat gene responds differently to ABA and osmotic stress at different developmental stages and in different tissues. Cat1 transcript accumulates to high levels in developing and germinating embryos, and in leaves. In embryos, Cat2 and Cat3 transcripts are up‐regulated only at very high ABA concentrations during late embryogenesis and in response to various concentrations of ABA in germinating embryos. Cat3 transcript is down‐regulated by ABA and osmotic stress in leaves. Accumulation of Cat1 transcript in response to osmotic stress is a consequence of increased endogenous ABA levels. Our data suggest that two separate pathways might be involved in the ABA‐mediated induction of Cat1 . The Vp1 trans ‐acting factor is required for maximum induction of Cat1 transcript in wild‐type ( Vp1 /—) and in W64A developing embryos; however, Vp1 is not required for inducing the Cat1 transcript in vp1 mutant developing embryos, nor in W64A germinating embryos or in leaves. Given the fact that the Cat genes have a known function, we hypothesize that the increase in Cat gene products in response to ABA is due, in part, to ABA‐mediated metabolic changes leading to changes in oxygen free radical levels, which in turn, lead to the induction of the antioxidant defense system.
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Guan et al. (1998) studied this question.