D ISCUSSION 



Dr. Duysens: I should like to point out two things which seem to 

 argue against the suggestion made by Mr. Becker that the light energy 

 is passed on to the photosynthetic reaction via a triplet state of 

 chlorophyll b. 



The striking similarity between the action spectrum of the fluores- 

 cence of chlorophyll a and the action spectrum of photosynthesis of 

 the many photosynthetic organisms investigated indicates that the 

 energy absorbed by the various pigments is passed on to the fluores- 

 cent (lowest singlet) state of chlorophyll a and in this way becomes 

 active in photosynthesis. It might now be argued that the energy is 

 passed from chlorophyll a to the triplet state of chlorophyll b. As far 

 as I know, no mechanism is known by which such a transfer will be 

 accomplished with high efficiency. 



There is further the fact that many algae do not contain chloro- 

 phyll b. The pigment common to all of them is chlorophyll a. Appar- 

 ently, an energy transfer from a back to a triplet state of b is, in 

 general, not necessary for photosynthesis. It seems therefore not neces- 

 sary to postulate that such a transfer back to b occurs. 



Dr. Kasha and Mr. Becker: The philosophy of our proposal concern- 

 ing energy transfer between chlorophyll a and chlorophyll b has 

 apparently not been made clear. Our aim was merely to point out a 

 possibility that had been overlooked previously. Most of the conferees 

 seem to have taken it for granted that we implied that energy transfer 

 from chlorophyll a to chlorophyll b (via triplet states) was a neces- 

 sary phenomenon, which was not our intention. 



Thus, in answer to Dr. Duysens' second point, it is obvious that if 

 algae do not contain chlorophyll b, energy transfer between chloro- 

 phyll a and b cannot be considered, in either direction. His statement 

 is not a valid criticism of our suggestion on energy transfer. 



In answer to Dr. Duysens' first point, it is true that there is no 

 highly developed mathematical theory to account for a transfer of 

 energy from the triplet state of one molecule to another. However, 

 such a possibihty is qualitatively very plausible and probably is quite 

 a common photochemical mechanism. Highly efficient excitation of 

 triplet states is common; the long lifetime of the latter makes a highly 

 efficient transfer of energy plausible. 



43 /K^^^^^L y 



