402 



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G. C. McLeod, G. A. Hudock, and R. P. Levine 



4r 



TIME (HRS.) 



Figure 2. Ratio of chlorophyll a to chlorophyll b (Cal Cb) during the first 

 five hours of exposure of a culture of y-2 to the light following 96 hours of 

 growth in the dork. 



The action spectrum for the formation of chlorophyll during regreening 

 was measured by illuminating cultures of dark grown yellow cells with wave- 

 lengths of monochromatic light-half band width ^-1 mu- obtained with 

 Bausch and Lomb interference filters backed with Corning Glass filters. 

 The intensity of the monochromatic light for the regreening experiments 

 was always below the level of saturation obtained with white light. The 

 chlorophyll formed was extracted and measured spectrophotometrically 

 (9,10)^ The effectiveness of the monochromatic light in chlorophyll ac- 

 cumulation was calculated as the reciprocal of the relative number of quan 

 to absorbed in different parts of the spectrum to produce the same quantity 

 of chlorophyll as produced with 650 mu illumination. 



The action spectrum of a 96 hour dark grown yellow cells shows maxima 

 at 420-445 mu, 650 mu, and 594 mu, and the relative efficiencies are in 

 this order. (Figure 3) There is a suggestion of a shoulder at 680 to 690 mu. 

 This spectrum agrees with the action spectrum of "greening" in etiolated 

 Avena seedlings, and with that of bleached Euglena cells ^' ' '''^); and, 

 the absorption spectrum of protochlorophyll . The action spectrum was also 

 measured at different chlorophyll levels. All procedures revealed that 

 there is a shift in the red portion of the spectrum during chlorophyll syn- 

 thesis. 



