PHASE RESETTING OF THE NEUROSPORA-CRASSA CIRCADIAN OSCILLATOR - EFFECTS OF INOSITOL DEPLETION ON SENSITIVITY TO LIGHT

The input pathway between the blue-light photoreceptor and the circadian oscillator of Neurospora crassa has not yet been identified. To test the hypothesis that an inositol phospholipid signaling system might be involved in blue-light signal transduction, phase resetting by light was assayed in the inositol-requiring inl strain under conditions of inositol depletion. Phase-resetting curves and dose-response curves indicated that cultures maintained on low inositol (25-mu-m) were several orders of magnitude more sensitive to light than those maintained on high inositol (250-mu-m). This difference in light sensitivity was a property of inositol auxotrophy and was not seen in the wild type or in an inositol-independent inl+ revertant. Phase resetting by temperature was not affected by inositol depletion, indicating that the effect on light resetting is specific to the light input pathway and is not the result of a change in the amplitude of the oscillator itself. The results indicate an indirect role for inositol metabolites in the light input pathway-one that is not likely to involve direct participation of an inositol phospholipid signal transduction mechanism.