SOME EFFECTS OF MONOCHROMATIC LIGHT ON OXYGEN EVOLUTION AND 

 CARBON DIOXIDE FIXATION IN CHLORELLA PYRENOIDOSA 



Max H, Hommersand 



One of the problems that is encountered in investigations of 

 chromatic transients and enhancement is that closely related 

 species or varieties of algae often differ in their responses to 

 treatment with monochromatic light, even when they appear to 

 possess essentially the same pigment complex. Recently, we have 

 investigated material of Chlorella pyrenoidosa , Emerson strain, 

 obtained from the Indiana University Algae Culture Collection, 

 #252. Our cells show chromatic transients having the same gen- 

 eral magnitude and wavelength characteristics as those described 

 in Chlorella pyrenoidosa by Myers and French^-^', but, so far, we 

 have failed to observe any sustained enhancement. Enhancement 

 was looked for both in polarographic studies on oxygen evolution, 

 and in experiments on the rate of fixation of labeled carbon di- 

 oxide in monochromatic light. In addition to chromatic transi- 

 ents, our material of Chlorella produces a large, negative oxygen 

 transient immediately after the light is turned off. This 

 transient has the same general shape as the one described by 

 French and Fork^ ^ in Porphyridium , and referred to by them as 

 photostimulation of respiration. 



Light-dark oxygen transients . 



We have measured light-dark oxygen transients in Chlorella 

 polarographically under conditions in which the base-line drift 

 was less than 3% of full scale per hour, and in which the steady- 

 state photosynthesis rate was maintained at the same level at all 

 wavelengths. A regimen was adopted in which the cells were given 

 monochromatic light for six minutes followed by fourteen minutes 

 of darkness. This allowed time for the photosynthetic rate to 

 become stable at all of the wavelengths tested, except possibly 

 in the region around 480m^. The dark period was sufficiently 

 long in most cases to allow the transient to return to the base 

 line. The negative transient varied linearly as a function of 

 the steady-state photosynthesis rate throughout the visible 

 spectrum. It was observed that the size of the transient was the 

 same, within experimental error, at all wavelengths when light 



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