Synchronous divisions in mass cultures of the ciliate protozoon Tetrahymena pyriformis 



SYNTHESIS IN SYNCHRONIZED CULTURES 



The rate of synthesis was estimated from the total cell volume in aliquots. One-ml. 

 centrifuge tubes in which the bottom was made into a uniform capillary were used. 

 The cells were densely packed into the capillary by centrifugal force and cell volume 

 was measured as the height of the column of cells, assuming complete packing in all 

 cases. In Figure 7 the cell volume per unit volume of culture is plotted on a log scale 

 together with the cell count. During heat treatment there is little if any multiplica- 

 tion, but cell volume is increased to three times what it was. However, after the end 



5.0 



x 



to 



3.5 



3</°C^ 



J-LTLTLTLnSXTLTL 



29°C< 



7.5hr 



, + .o'l 



3.0 - + 



! 



to ^ 



1 



J 



25 >§ 



2 



6 8/0/2 fit /6 /8 20 22 2V 26 



hours 



Figure 7. The continuous curve represents cell counts ; the broken 

 represents volume of cells per unit volume of culture. 



curve 



of treatment multiplication sets in at a rate faster than in the untreated culture. 

 (In this case no attempt was made to resolve multiplication into the steps in which 

 it occurs.) Synthesis continues however at a slower rate than in the untreated culture. 

 After 5 hours the multiplication rate decreases and synthesis speeds up, both to the 

 rate before treatment. The relative position of the two curves 5 hours after end of 

 treatment, as compared with the situation before heat treatment, indicates that nor- 

 mal cell size has become re-established. In the case presented in Figure 7 the culture 

 was diluted after the end of heat treatment. Otherwise it is not possible in one experi- 

 ment to demonstrate these effects, particularly the return to the normal rate of syn- 

 thesis and of multiplication many hours after end of treatment. We want to emphasize 

 that the dip in cell count after dilution is atypical and may be due to an error made in 

 the dilution. If this is correct the absence of synthesis in the first half-hour after dilu- 

 tion may also be erroneous. The inverse relationship between rate of synthesis and 



149 



