Circadian rhythm of tyrosine aminotransferase activity inGonyaulax polyedra

In Gonyaulax polyedra kept at 20 °C, tyrosine aminotransferase (TAT) activity exhibits a circadian rhythm with a maximum around CT 18. In some cultures, a second, smaller maximum is observed around CT 6. The rhythm persists in LL. After transfer to 15 °C, i.e., a temperature at which the cells become sensitive to photoperiodic cyst induction by short‐day treatment or by melatonin, the nocturnal (TAT) maximum is suppressed.