9 Extensions of photosynthetic experimentation* 

 by Otto Warburg, Dean Burk and Arthur L. Schade 



Kaiser- Wilhelm- Institut für Zellphysiologie, Berlin-Dahlem 



Chlorella pyrenoidosa was cultivated as previously described (Warburg & Burk, 

 1950) in acid culture medium prepared with water taken from a deep well. The 

 culture bottles filled with 200 c.c. medium were inoculated with 100 cmm. cells and 

 placed at a distance of 25 cm. from a 200 watt incandescent lamp in a water bath 

 at 25° C. and aerated with 5% carbon dioxide in air. After 24 hr., when the cells 

 had multiplied 4-fold, they were used for the experiments. No settling of cells 

 occurred during the culturing. 



I. Centrifuging 



The cells were centrifuged in thin layers in broad cups for so short a time that by 

 gentle shaking they could be resuspended in a few seconds. The use of strong, angle 

 centrifuging, such as we had at our disposal at Urbana two years ago, is to be 

 avoided. Heavily centrifuged cells are damaged, and partly destroyed by the process 

 of resuspending, especially when mechanical agents are employed. 



II. Use of Ammonia 



The photosynthetic efficiency of the cells after harvest was determined in culture 

 medium, the nitrate of which was replaced by ammonia at 1/10 the concentration 

 of the nitrate (0.15 g. NH4CI/I.). In such Solutions the assimilatory quotient of the 

 young cultures employed was always near 1 (cf. Myers, 1949). In experiments of 

 long duration the pH was not shifted to the alkaline side as could happen with 

 nitrate as a source of nitrogen, so that there was no danger of carbon dioxide 

 retention being developed. When the pH at the beginning of the experiment was 

 4.8, it was about 3.5 after 7 hr. of illumination. No influence of this acidification on 

 the efficiency was observed. It was a further advantage of using ammonia that 

 possible discussions as to whether the oxygen of the nitrate might have to be con- 

 sidered in the computation of the energy transformation were eliminated. 



III. Optical Arrangement 



The light source was a 200 watt high-pressure mercury lamp (Osram). A condenser 

 of the aperture 1 : 1 provided a parallel light beam from which the green line 546 



* Aus Symposia of the society for experimental biology Number V, Carbon Dioxide Fixation 

 and Photosynthesis. 1951. 



Zusatz 1961. Der methodische Fortschritt dieser Arbeit ist im wesentlichen die 

 Ausnutzung der chemischen Aktinometrie zur Messung der Lichtabsorption in 

 dem „trüben Medium" der Zellsuspensionen, sowie die Teilung des Lichtstrahls 

 mit 4 total reflektierenden Prismen. 



9 Warburg, Zellphysiologie 



