AGING AND SELF-INHIBITION 



881 



Figure 26.11 A shows that the rate declined Imearly with the logarithm of 

 the amount of extract added. Experiments at various light intensities 

 (fig. 26.1 IB) showed that the inhibitor affects the saturation rate in strong 

 light rather than the quantum yield in weak light, i. e., it acts like a catalyst 



Hi 



1.0 - 



on 



LlI 



> 0, 



0.9- 



0.7- 



-1.0 -05 0.0 as 1.0 1.5 

 LOG UNITS EXTRACT 



A 



2.0 



2.8 3.2 3.6 4.0 



LOG LIGHT INTENSITY, lux 



B 



4.4 



Fig. 



26.11. Effect of extract from aged Chlorella cells on photosynthesis of young cells 

 in 0.1 M KHCO3 (one unit = e.xtract from lO^ dried cells) (after Pratt l'J43). 



* 8 12 16 20 24 28 32 36 40 44 48 52 56 

 AGE OF CULTURE, days 



Fig. 26.12. Decline of photosynthesis in Chlorella vulgaris with age (after Pratt 

 1943). The rate in 4 day old cultures (taken as unity in the figure) was 8.5 to 

 10 mm. 3 02/(108 cells X min.). 



poison rather than like a narcotic (the difference between these two tyjies 

 of poisoning was explained in chapter 12, Vol. I). 



In a logical development of these observations, Pratt (1948-) then 

 studied the decline of photosynthetic activity of aging Chlorella cultures, 

 and found complete parallelism between this phenomenon and the ac- 

 cumulation of the growth-inhibiting substance. The study was made in 

 5% carbon dioxide in air, with 15,000 lux illumination (which, according to 



