405 



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



During regreening the saturation rate for photosynthesis increases until 

 the ratio of chlorophyll b to chlorophyll a reaches its normal value. After 

 this, the saturation rate remains relatively constant and the highest rate of 

 oxygen evolution is around 680 mu which agrees with photosynthetic action 

 spectra reported by other workers ^' ' for normal Chlamydomonas . 

 (Figure 5) 



chlamydomonas, y-2 



J u 



600 650 



wave length in m^ 



700 



Figure 5. Action spectrum for photosynthesis for a regreened culture of 

 the mutant y-2. 



Results from many laboratories V^^ emphasize that photosynthesis in- 

 volves two different photochemical reactions driven by different pigments. 

 Only when both reactions are proceeding in the correct proportions is the 

 maximum rate of photosynthesis attained. Measurements of the enhance- 

 ment produced by different combinations of wavelengths against pigment 

 concentrations shows that it varies from 1 .0 to 1 .74 as the total chloro- 

 phyll content goes from 0.5 to 1 .3 ug/lO° cells and the Ca/Cb ratio from 

 2.4 to 3.0. (Figure 6) The absence of an enhancement of photosynthesis 

 below 0.5 ug/10^ cells may be interpreted as the failure of pigment inter- 

 action. More detailed studies of the effects of wavelengths of light on 

 the partial reactions of photosynthesis are necessary to clarify the specific 

 roles of the different pigments during regreening. 



