I 



ACTION SPECTRUM OF PURPLE BACTERIA 



1187 



ful, even on the surface, this does not prove that phycobiHns are not pig- 

 ments primarily intended to permit photosynthesis deep under the sea. 



One may speculate — particularly in the light of Blinks' experiments — 

 whether photosynthesis with phycobilins may not be an older process than 

 photosynthesis with chlorophyll; perhaps, the development of the green 

 pigment and its substitution for the phycobilins have been the product of a 

 later development, in which plant life, originating in the depths of the 

 ocean, migrated to the surface and finally spread overland. 



7. Action Spectrum of Purple Bacteria 



Engelmann found, in his fundamental work on photosynthetically ac- 

 tive bacteria (1888) that, if a spectrum was thrown on their cultures, they 

 developed only in the absorption bands of the green pigment (which we 

 now call bacteriochlorophyll). Purple bacteria also contain numerous 

 carotenoids, with absorption bands clearly separated from those of bac- 

 teriochlorophyll (c/. fig. 22.21). French (1937) found that the action spec- 

 trum of Streptococcus varians (as determined by the rate of consumption of 

 hydrogen) sho\\Ti in figure 30.12 closely parallels its absorption spectrum 

 in the yellow and red part of the spectrum but does not show maxima in the 

 green or blue that correspond to the absorption bands of the carotenoids 

 (c/. Table 30. VIII). French concluded that the red carotenoid pig- 

 ments of purple bacteria are photosynthetically inactive. It must be 

 noticed that, from the spectroscopic point of view, the conditions in purple 



o 



< 



1/5 

 if) 

 < 



O 



LJ 

 < 



<r 



400 600 800 



WAVE LENGTH, m^ 



Fig. 30.12. Rate of CO2 assimilation of a very dilute suspension 

 of Streptococcus varians as a function of wave length of incident light 

 (after French 1937). Rate scale represents molecules CO2 X 100 per 

 incident quantum. 



