Circadian Phototransduction: Phase Resetting and Frequency of the Circadian Clock of Gonyaulax Cells in Red Light1

Abstract

Constant red light (RR) influences the Gonyaulax clock in several ways: (1) Phase resetting by white or blue light pulses is stronger under background RR than in constant white light (WW); (2) frequency of the rhythm is less in RR than in WW; and (3) the amplitude of the spontaneous flashing rhythm is greater in RR than in WW. The phase response curve (PRC) to 4-hr white or blue light pulses is of high amplitude (Type 0) for cells in RR, but is of lower amplitude (Type 1) for cells in WW. In all cases, the PRC is highly asymmetrical: The magnitude of advance phase resetting is far higher than that of delay resetting. Consistent with this PRC, Gonyaulax cells in RR (free-running period greater than 24 hr) will entrain to T cycles of between 21 and 26.5 hr. The bioluminescence rhythms exhibit "masking" by blue light pulses while entrained to these T cycles. The fluence response of phase resetting to light-pulse intensity is not linear or logarithmic--rather, it is discontinuous. This feature is consistent with a limit cycle interpretation of Type 0 resetting of circadian clocks. Light pulses that cause large phase shifts also shorten the subsequent free-running period. The phase angle difference between the clock and the previous LD cycle is within 2 hr of the same phase between 16 degrees C and 25 degrees C, as determined from the light PRCs at various temperatures. Several drugs that inhibit mitochondria and/or electron transport will partially inhibit the phase shift by light.

ldpA Encodes an Iron-Sulfur Protein Involved in Light-Dependent Modulation of the Circadian Period in the Cyanobacterium Synechococcus elongatus PCC 7942

“…In the eukaryotic alga Lingulodinium polyedrum (formerly Gonyaulax polyedra), a sublethal concentration of DCMU shortens the FRP (30). DCMU also inhibits phase shifting in response to a light pulse in L. polyedrum (19) and in Chlamydomonas reinhardtii (18). Thus, a connection between photosynthetic electron transport and light input pathways of the circadian system is a common characteristic among some phototropic organisms.…”

"What watch? ... such much!"* Complexity and evolution of circadian clocks

“…The other light input pathway responds both to red and blue light, possibly sharing pigments with the photosynthesis machinery. Pharmacological inhibition of photosynthesis affects the Gonyaulax circadian system (Johnson and Hastings 1989;Roenneberg 1994), and photosynthesis is itself an output of the clock (Prezelin and Sweeney 1977;Sweeney 1986). Thus, it represents a metabolic feedback loop.…”

Action Spectrum for Resetting the Circadian Phototaxis Rhythm in the CW15 Strain of Chlamydomonas

“…In Gonyaulax, the action spectrum for resetting the clock also exhibits blue and red peaks, but this spectrum is significantly different from the absorption spectrum for the photosynthetic pigments of Gonyaulax (11). In addition, DCMU does not inhibit phase resetting at concentrations that abolish photosynthetic oxygen evolution (10,14 (1), which is probably the mode of locomotion in soil. Thus, Chlamydomonas cells might easily find themselves in low-or high-light environments.…”