1840 



SPECTROSCOPY AND FLUORESCENCE OF PIGMENTS CHAP. 37C 



cence or phosphorescence of long duration) is indicated by the many 

 relations between the rate of photosynthesis and the intensity of the 

 emission. Both show saturation in the same region of light intensities; 

 both have a temperature maximum at about 35° C. ; inhibitors of photo- 

 synthesis, including azide, cyanide, hydroxylamine, dinitrophenol and 

 ultraviolet light, stop both photosynthesis and the "afterglow." 



2 



S 

 \ 

 </) 



h- 

 O 



O 



o 



UJ 



o 



z 



Ul 



o 



2 



10 20 



TIME AFTER ILLUMINATION (MINUTES) 



Fig. 37C.23A. Decay of "photosyiithetic luminescence" at 25° C. (after Strehler 

 1951). Curve A: Spinach, mustard leaf, Chlorella, spinach chloroplasts, washed mustard 

 chloroplasts. Curve B: Unwashed mustard chloroplasts. 



The action spectrum of excitation of the afterglow appears to be the 

 same as that of photosynthesis, in both green and red algae; in the latter 

 case, this includes the region of predominant phycoerythrin absorption. 



Five percent carbon dioxide reduces the emission by about 30%, com- 

 pared to that in pure nitrogen. 



All these observations are consistent with, the assumption that the emis- 

 sion observed by Strehler and Arnold is a chemiluminescence associated 

 with an energy-releasing back reaction between photochemical products, 

 which becomes more probable when carbon dioxide is absent and photo- 

 synthesis cannot take its course. 



Strehler (1951) made a similar study with a preparation of spinach 

 chloroplasts, in which a comparison of the kinetics of chemiluminescence 



