A PERSISTENT DIURNAL RHYTHM OF LUMINESCENCE IN GONYAULAX POLYEDRA

Abstract

The light emission from cultures of the marine dinoflagellate G. polyedra is 40 - 60 times greater during the night than during the day. If such cultures are placed in continuous dim light (100 foot-candles) a diurnal rhythm of luminescence persists; but if placed in continuous bright light (1500 foot-candles) the rhythm is damped, and no fluctuations occur in the light emission. The period of the rhythm is always close to 24 hours when the cells are kept under constant conditions, but it varies slightly depending upon the temperature and light intensity. The occurrence of rhythmicity is not dependent upon prior exposure to day-night lighting conditions. Cultures grown in bright light for one year show a diurnal rhythm when placed in dim light or darkness. Cultures kept in alternating light and dark cycles which are greater or less than 24 hours are entrained so that the period of the luminescence rhythm corresponds to the period of the light-dark-cycle. When returned to constant conditions, however, the period of the rhythm reverts to about 24 hours. "Training" or "memory" is therefore not involved. The phase of the rhythm under constant conditions is related to the time at which the previous light and dark periods occurred. Moreover, the phase may be shifted by interposing a non-repeated exposure to a different light intensity. The number of hours by which the phase is shifted in such experiments is dependent upon the intensity and duration of the light treatment, and the time in the cycle when it is administered.