INDUCTION OF PHASE SHIFT IN CELLULAR 



RHYTHMICITY BY FAR ULTRAVIOLET AND 



ITS RESTORATION BY VISIBLE RADIANT ENERGY' 



CHARLES F. EHRET 



Division of Biological and Medical Research, 

 Argonne National Laboratory, Lemont, Illinois 



When nondividing cells of Paramecium bursaha of complementary 

 mating types are mixed together during a sexually reactive phase, a 

 mass agglutination occurs that is known as the mating reaction. This 

 is normally followed by pairing of cells and conjugation of the 

 complementary types. In nature, the reactive phase occurs in the day- 

 time and the nonreactive, or weakly reactive phase, at ijiight. In the 

 laboratory it has been demonstrated that phase shifts can be induced 

 by visible radiant energy (Ehret, 1953, 1955a), that under constant 

 conditions of darkness and temperature an endogenous diurnal 

 rhythm persists (Ehret, 1953, 1955b), and that these relationships 

 hold equally for cells freed of the symbiotic algae that normally 

 inhabit the cytoplasm of this species (Ehret, 1953). 



In the course of an investigation of the dose-response relationships 

 for the determination of phase-shift action spectra, it became obvious 

 that radiant energy of the far ultraviolet region of the spectrum was 

 not only highly efficient in inducing phase shifts, but that the efficiency 

 was directly related to the phase stage during which the stimulus was 

 applied. It was further observed that the UV effect was almost 

 entirely photoreversible with visible radiant energy. This paper de- 

 scribes the results of such an experiment. 



METHODS 



Culture methods were essentially similar to those previously de- 

 scribed (Ehret, 1953). Chlorella-lcss cell populations of P. bursaria 



1 Work performed under the auspices of the U. S. Atomic Energy Commis- 

 sion. 



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