388 



Max H, Homme r sand 



03 



!02 



o 01 



Fig. 7o Uptake of sodium 

 acetate-l-Cl"^ (3 x IQ-^M) by 

 Chlamydomonas reinhardtii in 

 light and dark, and in the 

 presence of KCN or CCCP as 

 indicated. Far red illumina- 

 tion was provided from two 

 sides by 'sun-gun' lamps at a 

 total intensity of 15,000 ft. 

 candles each passed through 

 a Wratten #45 filter backed by 

 a Coming red sharp-cut filter. 

 The cells were pretreated for 

 20 minutes under the experi- 

 mental conditions before the 

 label was added. 



promoted uptake of acetate is dependent on the production of ATP 

 by photophosphorylation. If this is so, then photophosphoryla- 

 tion resulting in the formation of ATP that is consumed outside 

 the chloroplast must be CCCP sensitive. Conversely, the 

 additional ATP involved in light promoted acetate uptake may 

 possibly come from light-stimulated respiration, and the effect 

 of CCCP would then be due to an uncoupling of this respiration. 

 We are conducting experiments to test these alternative possibil- 

 ities. In any event, a CCCP-insensitive photo synthetic pathway 

 probably exists in living cells, and is lost during their 

 disruption in the preparation of isolated chloroplasts. 



Since the uncoupling of oxidative phosphorylation by CCCP 

 would have the effect of increasing the steady-state ADP/ATP 

 ratio in the cell, it may be that the induction of photosynthesis 

 requires moderately high levels of ATP that are lacking in cells 

 treated with CCCP. It has been shown that in isolated chloro- 

 plasts far-red light is more effective in the synthesis of ATP 

 than visible light^^), Our experiments on the effectiveness of 

 color and intensity of light in overcoming the induction lag in 

 oxygen evolution caused by CCCP can also be interpreted as 

 evidence that more ATP is synthesized in far red than in visible 

 light. Our data are in agreement with the suggestion that there 

 is a higher rate of ADP consumption and ATP production at wave- 

 lengths where absorption is predominantly by pigments of System I, 

 and, correspondingly, that there is a relative higher rate of ADP 



