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



Several photochemical reactions take part in the formation of the chloro- 

 plast pigments. A lag period is followed by a period of pigment synthesis. 

 (Figure 1) Hff 



Figure 1 . Synthesis of total chlorophyll, chlorophyll a and chlorophyll b 

 in regreening cultures of dark grown y-^. 



Little is known about the lag period in chlorophyll formation \°) . Its exis- 

 tence probably indicates that there are certain processes required to ini- 

 tiate a further production of protochlorophyll in the cell v) , Another 

 change, possibly taking place during the lag phase, is an increased energy 

 transfer from the carotenoid pigments to chlorophyll \°) . Our experiments 

 show that the lag period is not influenced by a variation of the intensity or 

 the wavelength of illumination. Following the lag period, the light inten- 

 sity controls chlorophyll synthesis. The minimal light intensity for chloro- 

 phyll synthesis is betv/een 10 and 20 foot candles. Repeated measurements 

 show the rate of chlorophyll synthesis increases almost linearly with an In- 

 crease in light intensity above 20-50 foot candles, reaches a maximum rate 

 at 2500 foot candles, and, thereafter, decreases as the light intensity in- 

 creases. 



The ratio of chlorophyll a to chlorophyll b is constantly changing during 

 regreening. At the start of regreening the ratio is 1 .3, increases 2.4 at a 

 total chlorophyll level of 0.5 to 0.7 ug/lO*^ cells, and reaches 3.0 at a 

 chlorophyll level of 1 .30 ug/lO^. (Figure 2) 



