Catalase gene expression in response to chronic high temperature stress in maize.

Catalase gene expression was characterized in the scutellum of maize seedlings grown at normal (25 degrees C) and elevated temperatures (35 and 40 degrees C). Chronic elevated temperatures reduce scutellar catalase activity most noticeably in the inbred lines W64A and R6-67, which express all three CAT isozymes (CAT-1, CAT-2, and CAT-3). The observed decline in catalase activity is primarily attributed to a decrease in the amount of CAT-2 isozyme, due to diminished levels of the Cat2 transcript. As CAT-2 activity levels are regulated by the trans-acting gene locus Car1, it is possible that the Car1 gene product is inhibited at the elevated temperatures. In maize lines null for CAT-2 or both CAT-2 and CAT-3, the relative levels of Cat1 transcript, although steady throughout the 10 days post-imbibition scutellar profile, are slightly higher with increasing temperatures. This might indicate that, in thermally stressed seedlings, the accumulation and/or stability of Cat1 mRNA might compensate for the lack of Cat2 transcript in a tissue where Cat2 mRNA normally accumulates during the developmental period examined. These observations, along with the drastic reduction in seed germination and seedling height at chronically elevated growth temperatures, suggest that developmental arrest, rather than oxidative stress, might be the cause for the observed results relative to Cat gene expression under such conditions.