BARRY COMMONER 



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MAGNETIC FIELD 

 Fig. 3. ESR signals from living Clilorella in the dark and various intensities of 

 white light. Modulation amplitude: 3 gauss. 



and by a colorless mutant. The signals obtained from the green 

 strain are essentially identical to those observed in Chlorella, both 

 with respect to g values, hyperfine structure, and the effect of light. 

 In contrast, the colorless strain yields a single ESR signal at about 

 g = 2.006, which shows no hyperfine structure, and does not respond 

 to illumination. Fig. 4 also shows that when R. ruhriun is examined 

 under instrument conditions which will resolve the hyperfine struc- 

 ture in the signals from green algae, a single signal at about g = 

 2.003 and a half-width of 7 gauss is observed. Although this signal 

 somewhat resembles component I of green algae, and is responsive 

 to light, a considerably more detailed study is required for any 

 further comparisons. 



Fig. 5 shows that the presence of CO^ has a characteristic effect 

 on these signals. In the dark, when only component II is present, 

 its intensity is reduced by the presence of 5% COo in air. When 

 this gas mixture is present, and the cells are illuminated, the in- 

 tensity of signal II is reduced but that of signal I is enhanced. 



The effects of various intensities of light on the two ESR signals 

 exhibited by Chlorella provides further evidence of their relationship 

 to photosynthetic processes. From data of the type shown in Fig. 

 3, it is possible to estimate, separately, the effects of light intensity 

 on the two ESR components. The meter deflection at the first 

 hyperfine peak at the low magnetic field side of the overall ESR 

 signal is due only to signal II (see Fig. 1) . On the other hand, the 



