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

Abstract

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¯avo-enzymes for their eects on circadian properties such as phase and period. We found that allopurinol, an inhibitor of xanthine oxidoreductase, speci®cally inhibits the period and phase eects 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 unaected.

Twilight Times: Light and the Circadian System

“…Allopurinol specifically inhibits the effects of white and blue light pulses given after CT 15, while it does not change the effect of red or blue pulses given before CT 1.5 (Fig. 7B) (82). Again, allopurinol not only affects phase shifting by light pulses but also lengthens the period specifically in blue or white light.…”

“…In contrast, xanthine oxidase activity can actually be measured in Gonyaulax extracts and is under circadian control, showing a 15-fold difference over the course of one cycle (Deng and Roenneberg, unpublished results). We had originally used allopurinol in a series of experiments testing the influence of inhibitors of pigment synthesis and of flavoproteins (82). Whether the flavoprotein xanthine oxidase is directly or indirectly involved in the light transduction mechanism is still an open question.…”

“…The effect of chemicals on the light PRC in Gonyuulux: (A) creatine, redrawn after Roenneberg and Taylor (76); (B) allopurinol, redrawn after Deng and Roenneberg(82).…”

Photobiology of the Gonyaulax circadian system. I. Different phase response curves for red and blue light

“…The xanthine oxidoreductase inhibitor allopurinol spe-ci®cally inhibits the blue-sensitive light input, selectively suppressing the strong advance phase shifts after CT15 (Deng and Roenneberg 1997). Similarly, the sensitization of the circadian light input by creatine is much stronger for short-than for long-wavelength light (Roenneberg and Taylor 1994).…”

Entrainment of the Human Circadian Clock

“…Both quantity and quality of light can act independently as zeitgebers in this alga because as in many plants (Roenneberg and Merrow 2000) and animals (see Doyle et al 2006;Doyle and Menaker, this volume), light reaches the Gonyaulax clock via more than one light receptor (Roenneberg and Hastings 1988;Deng and Roenneberg 1997). In the ocean, Gonyaulax migrates daily over large distances from nutrient-poor surface waters to nutrientrich depths (Roenneberg et al 1989).…”