702 



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



emitted quantum contains essentially all the energy of the original absorbed 

 quantum, so that there would be no possibility of emission if the energy had 

 been degraded by one or more reactions. 



It therefore appears that an understanding of the delayed light emission 

 might provide new insight into the mechanism of photosynthetic quantum 

 conversion. However, to assess the significance of the delayed light 

 measurements, we must determine whether the emission Is closely associated 

 with photosynthesis. 



The delayed light emitted at times longer than about 0.1 sec after 

 illumination is indeed intimately related to photosynthesis. There Is ample 

 evidence for the involvement of photosynthetic enzymes with the emission in 

 this time range (26, 27, 29)^ In addition, the delayed light at these longer 

 times Is emitted from functionally active chlorophyll, since the presence of 

 two photosynthetic pigment systems can be deduced from the direct evidence 

 of chromatic transients, and of changes in the tlrrie course of emission caused 

 by excitation at different wavelengths^ ^' 20/ 21). 



In the millisecond time range, much less evidence has been given for 

 direct involvement of the photosynthetic apparatus in delayed light emission. 

 Sweetser et al .(29) reported some effects of poisons on delayed light emission 

 from 4 msec to longer times. The present paper gives additional Information 

 about the effects of photosynthetic poisons on the fast delayed light decay. 

 We have measured the emission from 1 to 20 msec after illumination. Of those 

 poisons used, every one that was known to acton the first steps of photosynthesis 

 had a significant effect on the delayed light emission. The poisons may be 

 classed into several groups according to the way they affect delayed light. 

 These data imply that delayed light in the millisecond range is emitted from 

 functionally active chlorophyll. 



MATERIALS AND METHODS 



The delayed light emitted from 1 to 20 msec after the middle of an 

 illuminating flash was measured with a phosphoroscope-photomultlpller- 

 oscilloscope apparatus similar to one used by Dr. R. S. Beckerat the University 

 of Houston. This Instrument, built by one of us (J. B. D.) In collaboration 

 with Dr. W. A. Arnold, will be described in a later publication. The 

 exciting light was a 1 000-watt tungsten bulb, filtered by 8 cm. of 90% 

 saturated CuSO. solution, with the filaments focussed on the cells to give an 

 image of about 1 cm'^. 



