PHOTOBIOLOGY OF THE GONYAULAX CIRCADIAN SYSTEM .1. DIFFERENT PHASE RESPONSE CURVES FOR RED AND BLUE-LIGHT

Phase responses to red and blue light pulses were measured at differen t times during the circadian cycle (phase response curves, PRC) in the marine unicellular dinoflagellate Gonyaulax polyedra Stein. Pulses we re given during a 24-h period of darkness; thereafter, cultures were r eleased into constant dim red light for the assessment of phase and pe riod. The results confirmed earlier findings that the Gonyaulax circad ian system receives light signals via two distinct input pathways. Dur ing the subjective day and for the first 3 h of the subjective night, red and blue light pulses led to identical phase responses. For the re st of the circadian cycle, however, phase responses to pulses of eithe r red or blue light differed drastically both in their amplitude and d irection (advances or delays). Thus, the Gonyaulax light PRC is genera ted by two distinct light responses. One of these represents responses via a light input that is responsive both to red and blue light mainl y producing small delays. The other represents responses of a primaril y blue-sensitive input system leading to large advances restricted to the subjective night. Via feedback, the blue-sensitive light input app ears to be under the control of the circadian system.