Heavy Water Slows the Gonyaulax Clock: A Test of the Hypothesis That D 2 O Affects Circadian Oscillations by Diminishing the Apparent Temperature

Abstract

To test the hypothesis that deuterium oxide acts in circadian systems by simulating a lower environmental temperature, the effects of D2O on Gonyaulax polyedra were examined, where the period of the circadian rhythm of bioluminescent glow in constant environmental conditions is shorter at 16.degree. C than at 22.degree. C, and the phase of the glow peak relative to a light-dark cycle is advanced at 16.degree. C relative to 22.degree. C. Addition of low concentrations of D2O to Gonyaulax did not produce the same effects on period and phase as lowering the temperature; the free running period is lengthened and the phase is delayed. In the Gonyaulax rhythm, the effect of added D2O probably is not equivalent to lowering the temperature.