LUMINESCENCE OF PHOTOSYNTHETIC ORGANISMS 125 



Arnold : It is difficult to say that 3'ou do not, because there are no photomulti- 

 pliers sensitive for long wavelengths. Suppose it is considerably far into the red. 

 The curve that Davidson and I published, giving the identity of the spectrum 

 from the delayed light and the fluorescent light, was submitted to our statistical 

 analysis panel in Oak Ridge. If you use one test, the two curves are certainly the 

 same. If you use another test, they are systematically different and there is a 

 little radiation in the red. 



James Smith : This seems to me to be a very important thing to determine. 



Amon: I was interested in your remarks about the longevity of this effect in 

 various chloroplasts and in your comment that lyophilized chloroplasts retain this 

 activity but the freshly prepared chloroplasts do not. That seems to fit with the 

 observation that, if lyophilized chloroplasts are kept for a long time, only a small 

 activity in the Hill reaction is observed. In your case, if I followed it correctly, 

 the luminescence effect accounts for about 1% or perhaps less of the radiation 

 energy absorbed. 



Strehler : Much less than that. 



Amon: Then, would you not require a large level of photochemical activity 

 retention by the chloroplast preparation in order to observe the effect? 



Strehler: As a rough estimate, I would say that the yield in the lyophilized 

 preparations is not less than V4 of what reasonabl.y fresh chloroplasts emit. 



Amon: I think the point raised by Dr. Rabinowitch, as to why this effect 

 persists, could be explained by the fact that you need only a portion of the photo- 

 chemical level of activity, and only a small portion at that, in order to observe the 

 effect. 



Now, turning to questions on the physiological side, have you ever tried to 

 increase this hght emission? As I understand, you have a certain proportion of 

 the Hght which is not being absorbed or utilized, but thrown back. You work in 

 the absence of any normal electron acceptor, that is, without anj' CO2 fixation 

 reaction and in the absence of Hill reagents. 



Strehler : In the chloroplast studies, yes. 



Amon: Then, you are re-emitting a very small portion of the absorbed light 

 energy, while the chloroplast has a much higher capacit}-. 



Rabinowitch : How about oxygen? Isn't oxygen a Hill reagent? 



Strehler : The preparation may be reducing and thus exchanging oxygen. 



Amon : Can you increase this percentage of radiant energy that is thrown back 

 by adding electron acceptors? Of course, if you have oxj^gen you are providing a 

 sink for electrons. Can you increase it in some other way? It seems to me it would 

 be a very interesting effect. 



Strehler: If you have any ideas on how it might be done, we will be glad to try 

 them. 



Wassink : Just one additional comment on the discussion between Dr. Lumry 

 and Dr. Strehler, which I think is also pertinent to a comment that Dr. Arnon 

 made. Is it true that the properties of this chemiluminescence are very much the 

 same as the fluorescence both in the time course and in their relations to environ- 

 ment? 



One would expect that any sort of agent that would increase fluorescence might 

 also be expected to increase chemiluminescence. 



