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 seedlings grown under different light regimes. Plants grown in a 12 h light/12 h dark photoperiod (LD) show a distinct diurnal pattern with maximal Cat3 transcript accumulation late in the light period (CT 10, circadian time) and low to undetectable levels late in the dark and early light period (CT 22-02). The Cat3 gene is expressed at high and constant levels without any diurnal fluctuations in leaves of maize seedlings grown post-imbibition in constant dark DD) or constant light (LL). The circadian rhythm of Cat3 is inducible by transferring DD-grown plants and/or LL-grown plants to a 12 h (light/dark LD) or 12 h (dark/light DL) cycle. Entrainment of the rhythm requires a cyclic light signal consisting of one DL-transition ('light on'-signal) followed by one LD transition ('light off'-signal). When etiolated maize seedlings were treated with single light pulses of white light and different monochromatic light and transferred to constant darkness inn) a similar induction pattern of the Cat3 circadian rhythm was observed. Cat3 mRNA accumulates to peak levels 4 h after the light pulse; the next peak appeared 24-28 h later. Induction by far red-light (FR) exhibits characteristics 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 photosynthetic genes, the maize cat3 gene expression was used for comparison.