389 



Max H. Horamersand 



production and ATP consumption at wavelengths where pigments 

 belonging to System II absorb predominantly. 



Conclusions . 



The relationships between enhancement, chromatic transients, 

 and transients attributable to photorespiration are difficult 

 to assess. Enhancement appears to depend in some way on the fact 

 that absorption by the pigments of System I is not always effect- 

 ively overlapped in the far-red region of the spectrum by absorp- 

 tion due to pigments of System II. Where enhancement is absent, 

 as in our strain of Chlorella , the overlap of the two pigment 

 systems appears to be better than usual, and the photo synthetic 

 rate does not decline rapidly in the far red. 



Chromatic transients appear to be a measure of the difference 

 in the balance achieved in the utilization of light energy 

 absorbed by the two pigment systems, depending on the color of 

 light the cells are receiving. The largest transients produced 

 by wavelength shifts reflect the greatest differences in the 

 relative participation of the pigment systems in providing energy 

 for steady-state photosjmthesis. The respiration rate may play a 

 role in achieving this balance, and all factors probably combine 

 to sustain the maximum quantum yield. 



Light-dark transients have been interpreted both as a photo- 

 stimulation of respiration and as oxygen uptake in the reoxida- 

 tion of intermediates of photosynthesis inside the chloroplast. 

 In either case, changes in the magnitude of these transients 

 resulting from wavelength shifts provide a measure of the rate at 

 which already-formed patterns of energy transfer or utilization 

 are broken down and new ones are established. 



This investigation was supported by a research grant GB-424 

 from the National Science Foundation. 



Credit is due to Mr, Douglas Fambrough for his work on the 

 effects of far-red light on carbon dioxide fixation reported in 

 this paper. The excellent assistance of Miss Mary Thomas and 

 Mr. Carl Lundeen is also gratefully acknowledged. 



1. Myers, J., & C. S. French, J. Gen. Physiol. , 43, 723-736 

 (1960) 



