INDUCTION OF CYST FORMATION BY LOW-TEMPERATURE IN THE DINOFLAGELLATE GONYAULAX-POLYEDRA STEIN - DEPENDENCE ON CIRCADIAN PHASE AND REQUIREMENT OF LIGHT

Encystment, which at a temperature of 15 degrees C is photoperiodicall y controlled in Gonyaulax polyedra, can also be induced by a decrease of temperature, from 20 to 10 or 8 degrees C in the absence of photope riodic signals. The cyst-inducing capacity of the decrease in temperat ure depends on the circadian phase: in constant light, the maximum of sensitivity was found at the beginning of subjective night. In a light /dark cycle, however, cyst formation was reduced during dark phase, in dicating that light is required for the process of encystment. A simil ar light dependence was seen in the effect of the physiologically occu rring cyst inducer 5-methoxytryptamine, but not in the encystment resp onse to the protonophores monensin and nigericin.