24 



B. Rumberg, P. 3chmidt-Mende , J. Weikard and H. T. Witt 



proof that X and plastoquinone resp. is the electron acceptor of 

 water is given in the following experiment: We measured simulta- 

 neously with the extraction and recondensation of plastoquinone 

 and the corresponding disappearance and reappearance of the ab- 

 sorption changes at 515 mu the oxidation of water (by Op-produc- 

 tion measurements). Comparing such results (fig. 15) it can be 

 seen that the magnitude of the changes at 515 mu parallels the 

 rate of Op-production. On the other hand the changes at 515 

 parallels the changes at 25^ mu (fig. 13, 14). 



8. Reaction scheme 



The results show that plastoquinone reacts at the position of Z. 

 X is identical with plastoquinone or closely related to it. 

 Therefore we introduce in the already shown scheme instead of X 

 plastoquinone Q (18)(15). 



III. THE ACTION SPECTRA OF THE TWO SEPARATED REACTION 

 CYCLES I AND II 



The action of cycle I is optically represented by the absorp- 

 tion changes of Chl-aj at 45o mu and chemically by the rate of 

 reduction of oxSj, (i.e. benzylviologen) . The action of cycle II 

 is optically representated by the magnitude of the absorption 

 changes at 515 mu and chemically by the rate of oxidation of wa- 

 ter (Op-production). 



Pig. 15 (top) show the optically measured action spectra (11) 

 of the two separated cycles and on the bottom the chemical ac- 

 tion spectra are shown. (The optical action spectra could be 

 measured with a much higher precision than the chemical ones. 

 The chemical action spectra are preliminary ones.) The results 

 are in agreement with the Emerson-effect (2o): The peaks indi- 

 cate those types of chlorophylls which provide the two reaction 

 centres Chl-aj and Chl-a-j-j per energy migration with light ener- 

 gy (11). These different -feypes are noted in fig.lo. The long 

 wave-length limit for reaction cycle I is at '^ 73o mu, the long 

 wave-length limit for reaction cycle II is already at ,r^ 7oo mu . 

 The action spectrum for the reduction of plastoquinone was fur- 

 thermore investigated directly at 254 mu . It has a long wave- 

 length limit at 7oo mu in accordance with the measurements at 

 515 mu and of oxygen production. 



IV. THE COUPLING OF REACTION CYCLE I AND II 



1 . F irst demonstration 



Optically demonstrations of the existence of two coupled light 

 reactions were done in the following way: Kok (2) showed that 

 far red light causes oxidation of P 7oo at 7o3 mu and shorter 

 wave-length its reduction. Duysens (21) showed in red algae that 

 red light causes oxidation of cytochrome and shorter wave-length 

 its reduction. We showed in green plants (18) that far red light 

 causes oxidation of cytochrome while shorter wave-length causes 

 the reduction of X which reduce cytochrome in the dark. 



