Two Possibilities for Time Measurement in Synchronous Chlorella — Circadian Rhythm and Timing

Abstract

Endogenous rhythms with periods of about 24 h (called circadian rhythms) are common to all eucaryotic organisms (Edmunds, 1984). It is still unknown how such oscillations have arisen during the evolution. Pittendrigh (1966) suggested that in earlier times organisms which perform their DNA replication and cell division during the night may have an advantage because of the high UV radiation during the day. This might cause deletions of DNA by the formation of thymidine dimers. Another still open question is that concerning the number of clocks in an, even unicellular, organism. One suggestion is the presence of one central oscillator which controls the circadian output of different parameters, so called hands. A desynchronization of these parameters recorded as phase shifts indicates that the coupling with the oscillator is not tight and can be affected by changes in the environment.