96 



W. L. Butler and N. I. Bishop 



of Scenedesmus. The fluorescence measurements on the wild-type 

 Scenedesmus cells in Fig. 3 show the typical two-pigment con- 

 trol: The fluorescence yield is greater in 650-nm light than in 

 600-nm light and is markedly depressed by 690-nm light. 



One set of mutants, called "COg" mutants, fails to fix CO2 in 

 the light but will evolve O2 in a Hill reaction. The fluores- 

 cence measurements in Fig. 3 show that the fluorescence yield of 

 the "CO2" mutant is about 3 -fold greater than that of the 



8 



6 



RELATIVE 

 FLUORESCENCE 

 INTENSITY 







o 



in 



o 

 in 



000^ 

 o in au- 



ID to (DO 



I MM 



in (Dlt; 



ID CD CC o 



1 i M 



3 

 o 



K-lmin.H 



TIME 



Fig. 2. Relative intensity of fluorescence {\p < 710 nm) 



from spinach chloroplasts excited by low-intensity, 

 chopped, 650-nm beam in presence and absence of 

 constant, monochromatic, actinic beam of wavelength 

 indicated. Effect of lO'^M DCMU shown. 



