Light-induced phase responses in Gonyaulax are drastically altered by creatine

The mammalian phosphagen creatine has been shown to shorten the circadian period (tau) of the bioluminescence rhythm in the marine alga Gonyaulax polyedra from 23 to 18 hr. The studies described here concern the interactive effects of creatine and light, mainly on the bioluminescence rhythm. We have found that the tau-shortening effect of creatine is greater in blue light, suggesting that it acts on a blue-sensitive light input pathway. In addition, creatine affects the phase response mechanism in Gonyaulax, which is also known to be mainly blue-sensitive. The responses to 4-hr light pulses are dramatically increased under the influence of creatine. The unusual phase response curve (PRC) of the Gonyaulax circadian system, which has no phase delays in the early night, is changed in the presence of creatine to a more typical type 0 PRC, with delays of up to 12 hr. Creatine also amplifies the cells' phototactic response, suggesting that the blue-sensitive light input pathway is shared by the phase-shifting mechanism of the bioluminescence oscillator and the mechanism responsible for phototaxis.