BARRY COMMONER 



369 



g= 2.005 



'^y 



Fig. 5. ESR signals from living Clilorella after equilibration witii air and 5% 

 COo in air. Modulation amplitude: 3 gauss. 



meter deflection at which the pure signal II crosses the baseline (as 

 observed in the dark) can be due only to signal I. From these two 

 determinations, one can estimate the relative intensities of the two 

 components in the overall ESR signal. 



The effects of various light intensities on the two components at 

 two different temperatiues are shown in Fig. 6. At 29.5 °C signal I 

 is not observed under any conditions. Signal II exhibits a light- 

 saturation curve typically observed in photosynthesis which reaches a 

 maximum at 20,000 lux. At 12.8°C, component II shows a similar 

 effect of light intensity, except that saturation occurs at about 10,000 

 lux. However, at the lower temperature, illumination also induces 

 the appearance of the component I, which increases with light in- 

 tensity without exhibiting a tendency to saturate imtil an intensity 

 of 60,000 lux is attained. 



From kinetic determinations of the type discussed earlier in con- 

 nection with chloroplast studies (see ref. 5 for details), we find in 

 Chlurella a single time constant after onset of illumination (about 

 10 seconds) , and imder certain circumstances 2 time constants (about 



