743 



Constantine Sorokin 





TIME 



Fig. 1— Photosynthetic activity in the course of 

 eel 1 development. 



In prolonged measurements, the rate of photosynthetic gas 

 exchange declines in old cells from the very beginning of 

 observations (Fig. 2). In younger cells, photosynthetic rate may 

 greatly increase in the course of observations, even if cells are 

 suspended in a nitrogen-free medium (''"'^), 



Thus, the size and/or activity of photosynthetic apparatus may 

 Increase in younger cells even under conditions generally con- 

 sidered unfavorable for photosynthesis. Under the same and more 

 favorable conditions, the activity and/or the size of photosyn- 

 thetic machinery in old cells inevitably declines. 



The decline in the active part of photosynthetic apparatus 

 with aging of cells has been attributed to changes in the rate of 

 metabolic turnover: the increase in catabolic activity and the 

 decline in intensity of anabolic processes characteristic of the 

 process of cell development. An intense anabolic activity is 

 coupled in younger cells with higher capacity to use metabolic 

 intermediates for rebuilding photosynthetic machinery ('"» ^7), 



Respiration activity ('") and the capacity of cells for 



