The accumulation of Cat3 catalase mRNA in the green leaves of maize (Zea mays) exhibits an unusual circadian rhythm. The steady-state level of the Cad transcript varies dramatically over the day in seedlings grown on a 12-hr photoperiod. Low or undetectable levels of the Caf3 mRNA are found late in the dark and early in the light period, while the transcript accumulates to high levels late in the light and early in the dark period. This dramatic diurnal variation in mRNA level does not occur with the maize Cat] or Cat2 catalase transcripts. The diurnal fluctuation in Cat3 mRNA persists when the seedlings are transferred to continuous light or darkness, which indicates the influence of a circadian rhythm.
The catalase activity, CAT-2 and CAT-3 isozyme protein levels, and the steady-state mRNA levels for each of the three catalase genes were determined in the scutellum, root, epicotyl, and leaf of the developing maize (Zea mays L.) seedling. Catalase activity was highest in the scutellum, with 10-fold lower enzyme activity in the leaf and epicotyl. Very low levels of catalase activity were found in the root. The highest levels of CAT-2 protein were found in the scutellum, with about 10-fold lower levels in the green leaf.
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