SPATIAL AND TEMPORAL RESPONSES OF THE MAIZE CATALASES TO LOW-TEMPERATURE

Catalase (H2O2:H2O2 oxidoreductase, EC 1.11.1.6) is a primary antioxid ant enzyme that can remove H2O2 rapidly and prevent the formation of r eactive oxygen species. The maize (Zen mays L.) catalase genes are reg ulated in their expression spatially and temporally. Using embryos fro m germinating seeds and developing kernels from the maize standard inb red line W64A, which expresses all three Cat genes, and the CAT-2 null line A338F, we have examined the response of the three catalase genes to low temperatures (14 degrees C, 4 degrees C, or 14/4 degrees C). T otal catalase activity increased in response to low temperatures in ge rminating embryos of both maize lines. Zymogram analysis showed that t he increase in total catalase activity was due to accumulation of the CAT-1 and CAT-2 isozymes in the scutella and embryonic axes of germina ting embryos. In both lines, CAT-3 activity decreased in the embryonic axes of germinating embryos in response to low temperatures. The stea dy-state levels of Cat transcripts did not parallel the pattern of the corresponding catalase proteins, indicating the involvement of post-t ranscriptional control mechanisms. In contrast to germinating embryos and excepting an increase at 4 degrees C in A338F, total catalase acti vity decreased in response to low temperatures in scutella of developi ng embryos of both lines. CAT-2 activity (in W64A) and CAT-3 activity (in A338F) decreased in response to low temperatures and their corresp onding steady-state levels of mRNA also decreased. Only CAT-1 activity increased dramatically at 4 degrees C in A338E but Carl transcript le vel did not change. Our data indicate that the three maize catalase ge nes respond differentially to low temperatures at two different develo pmental stages.