403 



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



500 600 700 



wavelength in m^ 



Figure 3. Action spectrum of "greening" of a 96 hour dork grown culture 

 of y-2. The insert shows the shift of the red peck of the action spectrum 

 during chlorophyll synthesis. 



At a chlorophyll level of 0.5 to 0.7 ug/lO*^ cells the 650 mu peak broadens 

 to 680-690 mu. Above a chlorophyll level of 0.7 ug/lO^ cells there is a 

 shoulder at 650 mu and the major peak at 684 mu. The measurements do 

 not show a shift in a corresponding peak in the blue portion of the spec- 

 trum. 



Below chlorophyll levels of 0.5 ug/lO*^ cells the peaks in the action 

 spectrum are probably due to the absorption of protochlorophyll . The 

 broadening of the peak with further chlorophyll accumulation indicates an 

 increasing participation of chlorophyll a. It is fully active when the peak 

 shifts to 680 mu as the level of pigment approaches that of the light grown 

 cells. 



If a photosynthetic reaction is directly limited by the chlorophyll con- 

 tent it should decrease at the same rate as chlorophyll content in the dark 

 grown y-2. On return to the light, the rate of such a reaction would not 

 be expected to increase until after chlorophyll synthesis has begun. On 

 the other hand, the rate of a photosynthetic reaction which is not limited 

 by the chlorophyll content, but by other coincidental factors, will de- 

 crease at a different rate. 



A test of this hypothesis is to examine carbon dioxide fixation and ox- 

 ygen evolution during bleaching and regreening. The rate of carbon 



