ON THE VARIABILITY IN THE ACTIVITY OF THE 

 PHOTOSYNTHETIC MECHANISMS 



Constantine Sorokin 



Photosynthetic activity was observed to vary from one observa- 

 tion to another and in the course of one experiment. For example, 

 in measurements of the enhancement effect, the photosynthetic rate 

 and enhancement were changing over a considerable period of time 

 estimated to last for the red alga Porphyridium for about k 

 hours (Oo In Chlorella, the dark current was observed to drift 

 during the first 12 hours after placing cells upon the 

 electrode (2), and stabilization of photosynthetic oxygen produc- 

 tion required up to 2 or 3 days. Poor reproducibility and 

 inconsistency of the activity with time, even for the same batch 

 of cells, implied that some factor or factors were possibly over- 

 looked. 



Studies on photosynthetic activity in the course of the 

 development of algal cells indicated that the activity level does 

 not remain constant during the life cycle of cells. As a cell 

 proceeds in its development, the activity first rises during the 

 initial portion of the life cycle, attains a maximum in cells of 

 intermediate age, and then declines toward the time of cell 

 division (Fig, 1). 



One group of investigators observed the rising part of the 

 curve to coincide with the initial portion of the illumination 

 period and the declining part of the curve with the later portion 

 of the illumination period (3~7), Under conditions of synchro- 

 nization used by another group of researchers, the recovery of 

 the rate was accomplished before the beginning of illumination; 

 thus, the decline in the photosynthetic rate was usually 

 observed as extending over the whole light period \°* 9), 



A decline in photosynthetic activity beginning at some earlier 

 or later developmental stage is a common feature characteristic 

 of the life cycle of cells, Otd cells are sluggish (6), have 

 lower quantum efficiency ('0) , and are more sensitive to adverse 

 environmental conditions, particularly to the effects of strong 



light (^). 



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