748 



Cons tan tine Sorokin 



The duration of the period of intensive degradation under 

 unfavorable growth conditions is expected to depend on the 

 physiological state of cells and on external factors. Eventually, 

 with little left to undergo degradation, catabol ic processes also 

 decline to a minimum. In an impoverished cell, metabolic 

 activity is more or less stabilized at a low level. However, the 

 fact that the cell cannot be maintained in this state indefi- 

 nitely indicates that even under these conditions degradation 

 proceeds at a slow rate until the death of the cell. 



Thus, in a batch of nonsynchronized cells undergoing the so- 

 called starvation (2» 37), three groups of conplex processes take 

 place: the depletion of reserve materials in the process of 

 respiration, a change in the age composition of cells under 

 observation, and progressive degradation of metabolic mechanisms 

 due to absence of growth. Both moieties of the photosynthetic 

 apparatus, the one responsible for dark reactions and the other 

 constituting photochemical part of photosynthetic machinery, are 

 affected. An indirect evidence for the enzymatic part to be 

 affected by age changes and metabolic turnover comes from studies 

 on the degradation of enzyme proteins in bacteria and yeasts (3o) 

 as well as from observations on the decline in, the respiratory 

 and growth activity with the age of the cells (^o» '9). A more 

 direct proof is supplied by the fact that photosynthetic activity 

 in older cells is much lower than in younger cells under condi- 

 tions of light saturation where the rate of the photosynthetic 

 process is affected by enzyme activity '"). 



Indications for the photochemical part of the photosynthetic 

 apparatus to be affected by changes bound with cell development 

 and metabolic turnover are as follows: 



1. Studies on chlorophyll turnover in higher plants indicated 

 that chlorophyll undergoes a rapid degradation in older 



tissues (38JfO). 



2. Observations on synchronized algal suspensions demon- 

 strated that photosynthetic activity in older cells is inferior 

 to that of cells of intermediate age also at intensities below 

 light saturation where the rate of photosynthesis is assumed to 

 be dependent on photochemical reactions v*^), 



3. Fluorescence intensity for older cells was shown to exceed 

 that of younger cells (^2). with the inverse ratio existing 

 between fluorescence yield and photosynthetic activity, observa- 

 tions on the increase in fluorescence with the age of the cells 



