DEVELOPMENTALLY RELATED RESPONSES OF MAIZE CATALASE GENES TO SALICYLIC-ACID

The response of the maize catalase genes (Cat1, Cat2, and Cat3) to sal icylic acid (SA) was examined at two distinct developmental stages: em bryogenesis and germination, A unique, germination-related differentia l response of each maize catalase gene to various doses of SA was obse rved, During late embryogenesis, total catalase activity in scutella i ncreased dramatically with 1 mM SA treatment. The accumulation of Cat2 transcript and CAT-2 isozyme protein provided the major contribution to the observed increase in total catalase activity. This increase was paralleled by the enhanced growth of germinated embryos at that stage . In a CAT-2 null mutant line, a full compensation of total catalase a ctivity by the CAT-1 isozyme was observed in the presence of SA. This suggests that catalase is important for maintenance of normal cellular processes under stress conditions. SA at 1 mM, which enhances growth of precociously germinated embryos, appeared to inhibit seed germinati on at 1 day after imbibition. Furthermore, Cat2 transcript accumulatio n was inhibited at this stage. SA is probably not a direct signal for the induction of the catalase genes, Other signals, possibly germinati on-related regulator(s), might be responsible for the induction of the catalase genes. The effect of SA on the activity of purified catalase protein was also examined.