THE ENERGETICS OF PHOTOSYNTHESIS 



75 



§ 30 The Action of Blue-green Light 



When respiration is first compensated with white hglit, illumination with 

 red or green light gives good values for the quantum yield. Monochromatic 

 light itself at sufficient intensity would — without compensating white light — 

 also give manifold compensation. Warburg et al. (56, 60) found, however, that 

 without white light the yields become poorer and that they can be improved by 

 the addition of white light. In particular, it was established that the blue- 

 green part of the white light, i.e., that part of the spectrum which is absorbed 

 by yellow pigments, plays the active role. The addition of small intensities 

 of the light of the blue-green cadmium lines (4680, 4800 and 5090 A) proved 

 to be sufficient. As the action of the blue-green light sets in gradually and 

 also decreases gradually after removal, it was assumed that this light does not 

 directly influence photosynthesis. The required quantity is so small that, 

 by comparison with red or green measured light, from an energetic point of 

 view it can be ignored. 



Fig. 30. The action of blue-green light. 

 Continuous line : illumination with red meas- 

 ured light only (/ = 16.7 ^ul quanta/min). 

 Dotted line: additional illumination with 

 blue-green light (/ = 0.3 jul quanta/min) 

 (Warburg et al., Angew. Chem.). 



60 120 180 240 300 360 420 



min — >■ 



The curve of Figure 30 shows the result of an experiment in which blue- 

 green cadmium light is alternately added to and removed from the red meas- 

 ured light (6440 A). In analyzing the curve of Figure 30 we see that after 

 the addition of blue-green light (dotted line) the quantum requirement is 4.4 

 after 2 hours, corresponding to an efficiency of 59%. Removal of the blue- 

 green light increases the quantum requirement to infinity (efficiency = 0). 

 Addition of blue-green light again decreases the quantum requirement 

 to 3.6 (efficiency 72%). Removal of blue-green light increases the quantum 



