CIRCADIAN REGULATION OF THE CAT3 CATALASE GENE IN MAIZE (ZEA-MAYS L) - ENTRAINMENT OF THE CIRCADIAN-RHYTHM OF CAT3 BY DIFFERENT LIGHT TREATMENTS

The Cat3 maize catalase gene is a non-photosynthetic. non-chloroplast- associated gene that exhibits a transcriptionally regulated circadian rhythm. Cat3 transcript accumulation was examined in leaves of maize s eedlings grown under different light regimes. Plants grown in a 12 h l ight/12 h dark photoperiod (LD) show a distinct diurnal pattern with m aximal Cat3 transcript accumulation late in the light period (CT 10, c ircadian time) and low to undetectable levels late in the dark and ear ly light period (CT 22-02). The Cat3 gene is expressed at high and con stant levels without any diurnal fluctuations in leaves of maize seedl ings grown post-imbibition in constant dark DD) or constant light (LL) . The circadian rhythm of Cat3 is inducible by transferring DD-grown p lants and/or LL-grown plants to a 12 h (light/dark LD) or 12 h (dark/l ight DL) cycle. Entrainment of the rhythm requires a cyclic light sign al consisting of one DL-transition ('light on'-signal) followed by one LD transition ('light off'-signal). When etiolated maize seedlings we re treated with single light pulses of white light and different monoc hromatic light and transferred to constant darkness inn) a similar ind uction pattern of the Cat3 circadian rhythm was observed. Cat3 mRNA ac cumulates to peak levels 4 h after the light pulse; the next peak appe ared 24-28 h later. Induction by far red-light (FR) exhibits character istics of a very low fluence phytochrome response. Also blue light and ultraviolet light pulses cause induction of the Cat3 circadian rhythm , but do not influence the periodicity of Cat3 expression. In order to demonstrate differences of the Cat3 circadian regulation from photosy nthetic genes, the maize cat3 gene expression was used for comparison.