PHOTOREACTIONS Al.'D 5ESPIBATI0N 



George Hoch and Olga v. H. Owens 



Living cells obtain energy for self-synthesis by three 

 paths, they are: (1) dismutation of chemical compounds; (2) 

 oxidation of chemical compounds; (3) utilization of electro- 

 magnetic radiation. This symposium is concerned v;ith the 

 last process, photosynthesis. Photosynthesis is a particu- 

 larly apt name, but is used too often in a limited sense, 

 that is, the synthesis of sugar or sugar polymers from car- 

 bon dioxide and water at the expense of light energy. 



The purpose of our investigations was to determine the 

 relationship between two of these energy supply paths, 

 namely oxidation (as evidenced by respiration) and light 

 utilization. The subject has a long and somewhat varied 

 history, ranging from a suppression of respiration in the 

 light to an acceleration of large magnitude. In particular, 

 the effects occurring at low light intensities are interest- 

 ing, if for no other reason than how they affect measure- 

 ments of the quantum yield, chromatic transients and 

 Emerson "enhancement". 



(1 2) 

 Follov/ing the lead of Allen Brov/n and coworkers ' we 



have employed a mass spectrometer in these investigations. 

 The instrument has been described^3) and differs from others 

 in that it directly measures the gas concentrations dis- 

 solved in the liquid phase. 



Oxygen uptake and production at various wavelengths . 



Figure 1 describes the response of oxygen uptake ind 

 production to increasing light intensities of three wave- 

 lengths in Anacystis nidulans . This figure effectively 

 summarizes our results; although the effects may differ 

 quantitatively from day to day, the qualitative features 

 are consistent ''^•' . These features are that light given to 

 chlorophyll a suppresses oxygen uptake while light given to 

 the accessory pigment, phycocyanin, increases oxygen uptake. 

 The overall feature in chlorophyll a light is a broken 

 curve v/hen net oxygen exchange is plotted as a function of 

 intensity. This effect was first observed by Kok^5) and 

 has been termed the "Kok effect". 



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