REACTION PATTERNS IN PHOTOSYNTHESIS 83 



Discussion 



Rabinowitch : Dr. Witt, maj' I ask you, can you describe in a few words the 

 kind of flashes you used? 



Witt : We used a spinning wheel for the long flashes, and for the short flashes 

 we used electrical discharge tubes. 



Rabinowitch: For the longer flashes you simply used rotating discs in front of 

 what kind of light? 



Witt : In front of a tungsten light. 



Arnold : What was the position of the cells? 



Witt : Above the multiplier to catch all scattered light. 



Rabinowitch : How often did you flash this lamp? 



Witt : Up to 200 cycles a second. 



Rabinowitch : And it gave enough Ught to saturate? 



Witt: Yes. Only with 3.10"= second flashes did we observe a loss of the satura- 

 tion approximating 10%. 



Chance : Were you measuring at wavelengths other than 515? 



Witt: At 475; and not precisely at 420 and 555. We intend first to get informa- 

 tion about the change of absorption at 515 and 475 as a function of several param- 

 eters. Then we intend to go on to other wavelengths. 



Chance : But these fast and slow effects might be rather different at other wave- 

 lengths. 



Witt : Yes, I think so, and I hope to see the differences. 



Wassink: Have you ever extended the light period longer than what you 

 showed — to more than 1 second? 



Witt : Yes, we have seen marked changes of absorption from between 1 second 

 and 1 minute, after longer dark periods. 



Wassink: From what I remember of our fluorescent measurements they ex- 

 tend certainly much longer than something of the order of a few seconds. They 

 extend up to the order of a minute. 



French : Dr. Strehler will have some absorption curves for longer times. 



Wassink: Is that a definite end-phase you reach, or is something going on 

 after that? 



Witt : We measured all effects in the steady state of periodic flashing light, and 

 if you use long "flashes" you can see more — but slower — changes of absorption 

 with an end-phase after some minutes. 



Liunry: Just one observation. This is intriguing but certainly not a fact yet. 

 Those of us who have been working on quantitative Hill reaction characteristics 

 are concerned because we did not check the early work of Holt and French who 

 used 2,6-dichlorophenol indophenol as their oxidant. Also we did not check the 

 recent work of Tom Hill working in R. Hill's laboratory, and he uses this oxidant, 

 too. We have studied a lot of things with hydrogen ion evolution and oxygen 

 evolution in the reducing of the Hill oxidant. We find good agreement in these 

 reactions, but there are drastic differences between our results and those appar- 

 ently observed with the 2,6-dichlorophenol indophenol. So maybe the effect that 

 you have been showing here has been showing up all the time and we have not 

 grasped it imtil recently. 



