10 



L.N.M. Baysens 



Fig. 3. The difference spectrum with the blaok circles is 

 the abserbancy difference of the steady states in intense 

 light of 680 DM (light l) and in light of 620 mi (light 2), 

 and that with open circles is the absorbancy difference 

 at lower intensities, between the steady states in light 

 of 680 and 620 mji and in light of 620 mji alone. The bro- 

 ken curve is the difference of the spectra of oxidized and 

 reduced plastoquinone. The first spectrum indicates, 

 that besides oxidation of quinone in light of 680 n^ 

 other reactions occur. 



only a small fraction of the total amount of the quinones, which 

 are present in the chloroplast(at a concentration of about 1/10 

 of that of chlorophyll). It was not possible to conclude from 

 the difference spectrum, which of the numerous quinones dis- 

 covered in chloroplasts is the photoactive one. 



