PHOTOSYNTHESIS BY THE ETIOLATED PLANT 227 



thing that goes on in the dark that is not photochemical which then can be trans- 

 formed by the photochemical trigger. 



Tolbert: An additional point of interest is that the etiolated plant and the 

 greening process are not sensitive to ionizing radiation. You cannot prevent 

 greening and normal development of the photosynthesis apparatus by massive 

 dosages of ganmia radiation of the order of magnitude of 100,000 to 300,000 r. 



Limiry : Is there any evidence of spectral chlorophyll changes? As you convert 

 protochlorophyll to chlorophyll can you increase the density of the chlorophyll? 



James Smith : Well, you do get this change that I showed here, and whether 

 it is a change in the chlorophyll or whether it is a change in the environment that 

 causes the change in the spectrum, I don't know. 



Lximry : Is it ruled out that the spectrum shifts that we have observed in chloro- 

 phyll in vivo are due to organization of chlorophyll molecules? Must this now be 

 assumed to be a function of the absorptive act for each chlorophyll molecule or 

 can it be due to the nearby neighboring chlorophyll molecules? 



I was very much worried by Rabinowitch's and Jacob's conclusion (which I 

 think was their conclusion anyway) in the Journal of Chemical Physics that this 

 is not the kind of change— that we would observe too big a change in the spec- 

 trum, too much of a shift toward the red, if this was due to dipole-dipole inter- 

 action between neighboring chlorophylls and the like. 



References 



1. Tolbert, N. E., and Gailey, F. B., "Carbon dioxide fixation by etiolated plants 



after exposure to white light," Plant Physiol, SO, 491-499 (1955). 



2. Smith, J. H. C, "The development of chlorophyll and oxygen-evolving power 



in etiolated barley leaves when illuminated," Plant Physiol, 29, 143-148 

 (1954). 



3. Blaauw-Jansen, G., Komen, J. C, and Thomas, J. B., "On the relation be- 



tween the formation of assimilatory pigments and the rate of photosynthesis 

 in etiolated oat seedlings," Biochim. et Biophys. Acta, 6, 179-185 (1950). 



4. Irving, A. A., "The beginning of photosynthesis and the development of chloro- 



phyll," Ann. Botany {London), 24, 805-819 (1910). 



5. Tolbert, N. E., and Cohan, M. S., "Activation of glycolic acid oxidase in 



plants," J. Biol Chem., 204, 639-648 (1953). 



6. Schou, L., Benson, A. A., Bassham, J. A., and Calvin, M., "The path of carbon 



in photosynthesis. XI. The role of glycoUc acid," Physiol. Plantarurn, 3, 487- 

 495 (1950). 



7. Tolbert, N. E., and Cohan, M. S., "Products formed from glycoUc acid in 



plants," J. Biol. Chem., 204, 649-654 (1953). 



I 



