708 



Walter F. Bertsch, J. B. Davidson, and J. R. Azzi 



2. Hydroxylamine {]Q~^ fo lO'^M) af higher concentrations results in a 

 decay that approaches firstorder kinetics. From 1 to 8 msec (emission at longer 

 times was too dim to measure) cells poisoned with NHoOH (lO"'^ M) gave a 

 decay that was very nearly exponential. This decay is shown in Figure 4 

 (middle) for comparison with unpoisoned cells and with CMU-poisoned cells. 

 Concentration response curves for hydroxylamine sulfate are given in Figure 6, 

 which shows that at 1 0~3 M the emission at 1 msec was increased by more than 

 a factor of 2, while the 20 msec emission was too small to be observed with 

 our present apparatus. 



DISCUSSION 



Since the shape of the delayed light decay curve depends on intensity of 

 exciting light (Figure!), statements concerning the kinetics of the decay are 

 valid only in terms of the intensity of excitation. Our data at saturating 

 intensities of exciting light indicate that the decay from unpoisoned plants 

 has neither monomolecular nor bimolecular kinetics, in agreementwith Tollin 

 et al.(31). 



The differential actions of the poisons which we tested indicate that the 

 delayed lightatl to 20 msec must be emitted from functional chlorophyll that 

 is involved in photosynthetic quantum conversion. That is, every poison used 

 which was known to act on the first steps of photosynthesis had a strong action 

 on the 1 to 20 msec emission, whereas the poison (cyanide) that is known to 

 have no action on the first steps had no effect whatever on emission in this 

 time range. 



All the poisons which affected delayed light presumably act on reactions 

 involved in photosynthetic quantum conversion. We suspect that those com- 

 pounds that affected the intensity of emission without strongly affecting the 

 time course of delay (azide, 2-chIoro-6-nItrophenol) are not acting on steps 

 that are adjacent to photoreactions. These compounds seem to change the 

 number of electrons that may potentially emit delayed light without affecting 

 the processes by which the emission takes place. Poisons which drastically 

 changed the time course of emission (DCMU, CMU, orthophenanthroline, 

 hydroxylamine) must acton stepswhich are closely associated with the emitting 

 chlorophyll system. The extremely flat decay, and the 5- to 15-fold Increase 

 in intensity at 20 msec caused by DCMU, CMU, and orthophenanthroline, 

 suggest that these compounds may block electron or hole flow out of the 



