Introductory Remarks on the Luminescence of 

 Photosynthetic Organisms* 



BERNARD L. STREHLER, Biochemistry Departme7it, University of Chicago 



{Fels Fund), Chicago, Illinois 



In 19ol it was discovered (1) that green plants emit a low inten- 

 sity chemikmiinescence when they are illuminated. This luminescence 

 persists for some time (up to 200 minutes) after the plants are re- 

 moved from the light (2). Inasmuch as this process undoubtedly 

 represents a minute reversal of early steps in the conversion of light 

 energy to chemical energy and since it is easily measurable, the 

 phenomenon furnishes a useful tool for the study of the photochem- 

 istry of photosynthesis. Moreover, a solution of the intermediary 

 chemistry leading to this bioluminescence in all likelihood will also 

 have a direct bearing on the understanding of its converse process, 

 photosynthesis. 



The salient features of this phenomenon are as follows. 



PHYSICAL PARAMETERS OF PROCESS 



1 . The emitting molecule is chlorophyll a, as is shown by the color 

 of the emitted light, which is identical within experimental error to the 

 fluorescent light emitted (owing to chlorophyll a) by green plants 



(3). 



2. The efficiency of different wavelengths of exciting light in pro- 

 ducing luminescence parallels their efficiency in promoting photo- 

 synthesis (1). The action spectra of green plants (Chlorella) parallels 

 chlorophyll absorption, whereas in certain blue-green algae the ac- 

 tion spectrum follows that of phycocyanin absorption (4). Tn this 

 case fight absorbed by chlorophyll is inactive (or highly inefficient) 

 in promoting either photosynthesis (5) or chemilumescence, although 

 the emitting molecule is chlorophyll (4). 



3. Brown, red, green and blue-green algae and all green plants tested 

 (about 50 different species, including conifers), exhibit the phe- 



* This work was supported in part by a grant from the United States Atomic 

 Energy Commission. 



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