Photobiology of the Gonyaulax circadian system .2. Allopurinol inhibits blue-light effects

Light is the main environmental signal (zeitgeber) for practically all circadian systems, but little is known about the transduction mechanisms by which light signals reach the circadian oscillator. To identify components involved in the circadian light transduction pathway in the unicellular alga Gonyaulax polyedra Stein, we assayed inhibitors of pigment synthesis and of flavo-enzymes for their effects on circadian properties such as phase and period. We found that allopurinol, an inhibitor of xanthine oxidoreductase, specifically inhibits the period and phase effects mediated by the blue-light-sensitive input pathway, while the other light input of the Gonyaulax circadian system, that is sensitive to both red and blue light, appears to be unaffected.