UTILIZATION OF FAR-RED LIGHT BY GREEN ALGAE AND THE 

 PROBLEM OF OXYGEN EVOLUTION 



H. Gaffron, W. Wiessner and P. Homann 



The overriding interest in recent research on photosynthesis 

 of green plants (in contrast to that of bacteria) is the action of 

 monochromatic light of different wavelengths and the nature of the 

 Emerson effect. The latter is defined as the inefficiency of 

 absorbed light beyond X 700 mp. in promoting normal photosyn- 

 thesis and the partial restoration of this low efficiency when light 

 of shorter wavelengths is given simultaneously. The work sum- 

 marized below gives a possible answer to the question whether 

 the energy of far-red light is mainly lost unless combined with 

 the energy contained in larger light quanta, or whether the 

 absence of oxygen evolution only means that as the result of 

 monochromatic illumination beyond X 700 mfjt another metabolic 

 process takes over which is not connected with a visible gas 

 exchange. There are no observations which prove that light of 

 wavelengths longer than X 700 m|jL can by itself support a com- 

 plete metabolic process in normal intact green algae. Such a 

 metabolism ought to be sufficiently different from photosynthesis 

 so as not to require a concomitant evolution of oxygen, i. e. , it 

 should resemble at least outwardly the photometabolism of purple 

 bacteria. Photoreduction with hydrogen in adapted algae and 

 photometabolism of acetate fulfill this postulate. We have found 

 that both can be promoted very efficiently by far-red light alone. 



PHOTOREDUCTION WITH HYDROGEN IN THE NEAR INFRARED 



The gas exchange in a suspension of Scenedesmus cells in 

 very weak bicarbonate buffer under H2; 4% CO2 is measured 

 either manometrically or by means of a glass electrode which 

 records pH changes. With unadapted cells a normal rate of 

 photosynthesis can easily be demonstrated with visible light of 

 a wavelength which is absorbed by the algae as weakly as light 

 at X 705 m|j.. In the far-red of equal intensity oxygen evolution 

 and carbon dioxide reduction proceed very poorly. When both 

 lights are superimposed the yield is clearly much better than the 

 sum of the yields obtained by each of the two lights alone. 



436 



