25 



B. Rumberg, F. Schmidt-Mende , J. Weikard and H.T. Witt 



The above reported results shorn that when under natural con- 

 ditions (chlorella) there exists a coupling between the reaction 

 cycle I and II, it should be possible to demonstrate the coupl- 

 ing of the cycles I and II through the absorption changes of 

 Chl-a-. directly at ^3o mu . (Because of the strong fluorescence 

 in the red region a coupling at 7o3 mu can directly not be de- 

 monstrated) . 



On the other hand we selected with plastoquinone a first che- 

 mical representative of cycle II and it should be possible to de- 

 monstrate the coupling of cycle I and II also at 25^ mu. 



J^ccording to the action spectra Ghl-a-j- can be oxidized with 

 light a^ 7oo mu, i.e. 72o mu (decrease at 43o mu) and Chl-a-j- 

 should be reduced with -^7oo mu light, i.e. 55^ mu (increase at 

 430 mu). 63^ mu light produces namely reduced plastoquinone (Q,~) 

 and when there exists a coupling between reaction cycle I an.d II, 

 Q~ should provide Chl-at with electrons. Vice versa plastoquinone 

 can be reduced with -=• 7do mu light, i.e. 53'^- mu (decrease at 254 

 mu) and Q~ should be oxidized with >'7oo mu light, i.e. 72o mu 

 (increase at 254 mu). 72o mu light produces namely Chl-at (see 

 above) which accepts the electron of Q," when there existi a coupl- 

 ing between reaction I and II. The results in fig. 17 confirm 

 these predictions. 



2. Second demonstration 



It should be pointed out that as yet in all cases coupling of 

 two light reactions in photosynthesis was demonstrated only by 

 two different light colours. The following experiments show a 

 different and completely independent demonstration of coupling. 



We separated chemically the reaction cycle 1 from cycle II and 

 investigated the different properties of these separated reac- 

 tions (chloroplasts of spinach) (1o)(2o)(1). 



Some typical properties of reaction cycle I are for instance: 

 a) pH-range between 4-11; b) independence from the presence of 

 CMU. (CMU blocks water oxidation); c) practically independent 

 from aging. 



Corresponding properties of reaction cycle II are: a) pH-ran- 

 ge between 5 - 8; b) strong dependence from the presence of CMU; 

 c) strong dependence from aging. 



'/iThen however both cycles are completely coupled (fresh chloro- 

 plasts with Hill-oxidants ox.Sj or whole chlorella cells), the 

 behaviour of reaction cycle I ^demonstrated for instance by ab- 

 sorption at 7o3 mu) and the behaviour of reaction cycle II (de- 

 monstrated for instance by absorption changes at 515 mu)should 

 show one and the same dependence as function of pH, CMU age, etc. 



Figs.18-2o show the result. The influence is the same at both 

 wave lengths (5). This proves in a completely different way the 

 quantitative cooperation between both reaction cycles (5). 



