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SUMMARY 



and used by most participants; also "long wavelength system") 

 is sensitized mainly by chlorophyll _a; system II involves the 

 accessory pigments plus some in vivo forms of chlorophyll a. 

 The areas of greatest activity now cover the precise nature 

 of the biochemical events set into motion by illumination of 

 each of these pigment systems, and the mechanism for coopera- 

 tion between the two. 



Relatively little discussion or new information was pre- 

 sented at this meeting concerning the mode of energy transfer 

 from the initial light absorbing pigment molecules, to the 

 "quantum conversion centers" (alternatively - active centers, 

 sinks). Past arguments concerning the existence of electron 

 or hole migration in the chloroplast lamellae appear to have 

 subsided, and resonance transfer is looked to by most for the 

 method of energy transfer to the trapping centers (Duysens, 

 Rabinowitch). The photosynthetic unit, according to one re- 

 port (Kok) may be smaller than has been accepted until now. 



No evidence was presented directly related to the intimate 

 mechanism of the conversion of excitation energy to oxidation 

 reduction energy at the trapping center. However, a very 

 general underlying assumption is that the primary result of 

 this mechanism is the creation of a negative potential elec- 

 tron donor and a positive potential electron acceptor. 



Several laboratories report the direct observation of 

 small amounts of long wave absorbing pigments (Olson, Butler). 

 These arouse great interest because they could serve as sinks 

 for migrating excitation energy; and hence they should be at 

 the heart of any conversion center. For the same reason, 

 attention is being paid to pigments having fluorescence emis- 

 sion bands at long wavelengths. These were recently observed 

 at very low temperatures, and have been studied intensively 

 both in vivo and in solutions of chlorophyll (Brody). The 

 same considerations add great interest to the findings that 

 a minor fraction of chlorophyll, having an absorption band 

 at longer wavelengths is the only chlorophyll present in 

 distinct spatial orientation (R. Olson). 



Since quanta absorbed by the two pigment systems have 

 complementary functions, it is clear that there must be two 

 distinct conversion centers (although it is still possible 

 that one conversion center is actually the photo-activated 

 form of the other — a mechanism proposed by Franck). Studies 



