REGULATION OF THE CYCLIC REPRESSION OF THE CAT3 CATALASE GENE IN MAIZE LEAVES AND ROOTS OCCURS VIA THE DARK LIGHT TRANSITION

The maize (Zea mays. L.) Cat3 catalase gene is a nonphotosynthetic, no nchloroplast-associated gene regulated by a circadian rhythm. S1 nucle ase protection assays were used to examine Cat3 expression in maize se edlings. The data show a diurnal oscillation in Cat3 RNA levels in roo ts as well as leaves. The amplitude of the oscillation in roots is muc h less than that of leaves, and the root RNA accumulation appears to l ag behind leaf RNA accumulation. Altered photoperiods do not affect th e time course of Cat3 accumulation; instead, Cat3 levels peak approxim ately 10 hours after the dark/light transition regardless of the lengt h of the light period. Experiments with plants grown under a 12 hour/1 2 hour (12 h/12 h) light/dark cycle and transferred to continuous ligh t or darkness show that diurnal variations in Cat3 transcript accumula tion damp to continuous high levels under both conditions, confirming that the circadian rhythm in Cat3 RNA levels is due to the cyclic repr ession of Cat3 expression.