406 



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



E 1.4- 



^g of Chlorophyll/ 10^ cells 



Figure 6. Development of the enhancement of photosynthesis produced by 

 650-680 mu against chlorophyll content. 



The regreening process offers a unique opportunity to study the depen- 

 dence of photosynthetic capacity on chlorophyll synthesis and other co- 

 incidental factors. The kinetics of the decrease of the rate of C02 

 fixation in preparations of dark grown cells, and the kinetics of the in- 

 crease upon return of the cells to the light is essentially identical to the 

 change in chlorophyll content. It is clear that the fundamental reaction 

 of oxygen evolution begins when only a small amount of chlorophyll is 

 preserit in the cells, and in the absence of highly organized structural 

 units ^^^). The rapid increase in the rate of oxygen evolution at a critical 

 chlorophyll level suggests that either new structures must be built or new 

 components must be formed for the development of an active photosynthe- 

 sis. These structures could then provide for physical separation of products 

 and even for their transport to regions of the cells suitable for their pro- 

 tection and metabolism. It is certain that the proteins particularly the 

 chloroplastic proteins play a predominant role since the function of the 

 chlorophylls not only depends on the activity of several enzymes, but also 

 on photochemical reactions in which the properties of the pigment protein 

 complex are essential features. Several forms of this complex appears to 

 exist and to be able to change into one another during development. The 

 regreening cell is a dynamic system whose photosynthetic capabilities are 

 bound to the chloroplast (including structural features) and vary with the 

 environmental conditions. 



