EFFECTS OF PHOTODYNAMIC TREATTffiNT, ULTRAVIOLET RADIATION AI© 

 GAMMA RADIATION ON THE PHOTOSYNTHESIS AND HILL REACTION 



OF CHLORELLA 

 John D. Spikes and Dennis C. Hall 



Our research program has been concerned primarily with kinetic 

 studies of the f err i cyanide and quinone Hill reaction of isolated 

 chloroplasts of higher plants(1^2}^ In addition^ we have done 

 some comparative work on the photosynthesis and whole-cell 

 quinone Hill reaction of Chlorella(3) . V/e have heen especially 

 interested in mechanisms of energy absorption, transfer and 

 utilization in chloroplast systems as yell as in the water- 

 splitting process of the Hill reaction'^-'. More recently we have 

 expanded our program to include a somewhat simpler photochemical 

 phenomenon, photodynamic action. Photodynamic action may be 

 defined operationally as the killing or chemical alteration of an 

 organism, cell, or virus, or the chemical alteration of a mole- ■ 

 cule by light in the presence of molecular oxygen and an appro- | 

 priate photosensitizing dye(5;6). In this process, light energy 

 is absorbed by the sensitizing dye and then transferred in some 

 manner to the substrate system. :J 



In a sense, energy transfer mechanisms in photosynthesis and 

 in photodynamic action may be considered analogous, since long- 

 lived, light-excited states of the sensitizing pigments are 

 apparently involved in both cases. If energy transfer from 

 excited chlorophyll in a cell is prevented, the energy will be 

 used in reactions inhibitory or destructive to the photosynthetic 

 apparatus. In many cases these destructive reactions are photo- 

 dynamic in nature (see (7) and (°) for reviews of this field). 

 Photosynthetic cells lacking carotenoids are rapidly destroyed 

 under aerobic conditions in the light in what is apparently a 

 chlorophyll- sensitized photodynamic process^"/. 



This paper is concerned primarily with studies on the photo- 

 dynamic inactivation of the photosynthesis and whole-cell quinone 

 Hill reaction of Chlorella in the presence of added dyes. For 

 comparative purposes, some data on the inactivation of these same 



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