Reaction Patterns in the Primary Process of 



Photosynthesis 



H. T. WITT, Physikalisch-chemisches Institut der Universitdt Marburtj, 



Marburg/ Lahn, Germany 



In the primary process of photosynthesis hght is absorbed in- 

 directly or directly by chlorophyll. During this process the chloro- 

 phyll or chlorophyll complex changes into an unknown excited state. 

 With the aid of the energy of this state water is split in an unknown 

 way into oxygen and hydrogen (1). In a secondary process this hydro- 

 gen reduces carbon dioxide to carbohydrates. You know of the great 

 success in the investigation of this carbon dioxide cycle here in Amer- 

 ica (2). But there is little knowledge about the first step which trans- 

 forms light into free chemical energy. A special state of chlorophyll 

 during photosynthesis has not yet been observed. Furthermore we 

 cannot tell anything about the mechanism of hydrogen production 

 because the usual methods, for instance, the measurement of oxygen 

 production, are not sufficient to detect the fast reaction in the pri- 

 mary process. 



We have tried to measure reaction patterns in the primary process 

 by looking for fast changes of ahsorption immediately after flashes of 

 light (3). 



These changes of absorption cannot be detected by the usual type 

 of absorption measurements because the reactions are very fast and 

 the changes very small. There are, furthermore, technical complica- 

 tions due to the scattering of the incident light by the plants. There- 

 fore we have developed a sensitive apparatus by which we could 

 measure absorption changes in times between '-^10 ~^ second and sev- 

 eral seconds.* 



The experiments were made with various leaves, Chlorella, and 

 chloroplast.«. The photosynthesis was induced by periodic flashes of 

 light. The spectrum of the flash lay between 620 m/x and 700 ni/x. 



* Changes of the absorption in steadj' light were reported in connection with 

 redox reactions of cytochromes and pyridine nucleotides (4). 



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