BESSEL KOK AND GEORGE HOCH 



•105 



have strong indications that not all available "P 700" is necessarily 

 involved in these cyclic changes (at least in weak intensity flashes) . 

 They represent only "Avigglcs" of concentration and onr measurements 

 revealed that the hatkground level, on which they are superimposed, 

 is not constant. This backgroiuid level of "P 700" (the envelope of 

 the wiggling curve) progressively decreases if a steady sequence of 

 Hashes absorbed by chlorophyll a is applied. This is easily under- 

 stood. If each flash bleaches more pigment than the back reaction 

 can restore during the intermediate dark period, all available "P 700" 

 will disappear in the course of a few seconds. 



Surprisingly, however, if the activating light excites accessory pig- 

 ment, the background level of "P 700" increases (Fig. 5) . This hap- 



E 4 



UJ 



2 ■ 



UJ ' 

 UJ 



E-2 



cr ■J 

 o 



to , 

 m -4 



< 



-5 



FAR RED 



ANACYSTIS 



B-W 



A-B 



690 700 710 720 



WAVELENGTH m^ 



730 



Fig. ;>. Change of absorption around 700 ni/x induced in Anacystis cells by either 

 red light (X 580-6r)0 itim crosses, circles) or far-red light (\ > 650 m/i, solid circles, 

 squares). Both curves represent the background concentration of "V 700." The 

 dashed curve shows the fast reversible change having negative sign only (from 16). 

 .\-B: fast photochemical bleaching. B-W: change of background absorption level. 



