406 



LIGHT AND LIFE 



pens even if chlorophyll a is excited simultaneously and the flashes 

 of mixed wavelengths induced considerable direct photochemical 



bleaching. 



The obvious conclusion is that formation of "P 700" (during the 

 dark periods) is stimulated by light absorbed by accessory pigment, 

 and that there occur two light reactions with opposing effects. 



The experiment described in Fig. 6, and made with whole Anacystis 

 cells, demonstrates the above phenomena. The dotted curve shows 

 the activation spectrum of the fast absorption decrease (discussed in 



UJ 

 OS 



+ 3 



+ 2 



+ 1 



4. 



E 



o 



UJ 



I 



" 



z 

 o 



t 



CE 

 O 



to 



4 -I 



ANACYSTIS 

 -• B-W Ir 



100 % 



— O B-W Iq = 3% 



•X- A-B Iq : 100% SCALE X 10 



-4 



_L 



_L 



o 



_L. 



400 



700 



500 600 



WAVELENGTH OF ACTIVATING LIGHT 



Fig. 0. Activation spectra of the 700 ni^ al)soiption sliifls measured witli llie long 

 dark-time arrangement and whole Anacystis cells. Open circles, background signal 

 /„ 3%; solid circles, background signal /„ 100'/,; crosses, fast reversible change 

 I, 100%. A-B: fast photochemical bleaching. B-W: change of background ab- 

 sorption level (from 17). 



