740 



John D. Spikes and Dennis C. Hall 



increasing dose of gamma irradiation is similar to that reported 

 for ultraviolet irradiated leaves\21j. 



Algae in which photosynthesis was inactivated by photodynamic 

 treatment; or by acute doses of ultraviolet or gamma radiation^ 

 showed a large uptake of oxygen on illumination. The rate of 

 uptake was many- fold greater than the respiratory rate. In 

 inactivated algae the chlorophyll excitation energy probably 

 cannot be channeled into useful reactions and is therefore 

 available for the photooxidation of endogenous organic compounds. 



In summary^ we would like to suggest again the use of radi- 

 ation as a tool of the "specific inhibitor" type in the eluci- 

 dation of photosynthetic mechanisms. The present experiments^ 

 although very preliminary, do demonstrate the differential 

 effects of radiation on the photosynthetic and Hill reaction 

 activities of Chlorella. Because of the possibility of using 

 selective dyes, the photodynamic inactivation approach appears 

 to be the most useful. 



ACKNOWLEDGMEIfTS 



This research was supported by the U. S. Atomic Energy 

 Commission under Contract No. AT(i1-1)-875' The authors wish 

 to express their thanks to I-liss Marilyn K. Odell and Miss Rose 

 Bengal for excellent technical assistance. 



REFERENCES 



(1) Lumry; R., Mayne, B.C.^ and Spikes, J.D., Discussions 



Faraday Soc . 27:li^9-l60 (l959). 



(2) Rieske, J.S., Lumry, R., and Spikes, J.D., Arch . Biochem. 



Biophys . 97:100-106 (1962). 



(3) Spikes, J.D., and Fassell, G.IT., pp. i+ 71-^73 in Proc. 



Third International Congress Photobiology (Eds. B. 

 Chr. Christensen and B. Buchmann), Elsevier Publishing 

 Co., Amsterdam (1961), 

 (k) Lvmry, R., and Spikes, J.D., Rad . Res . (Supplement) 

 2:539-577 (i960). 



(5) Blum, H.F., Photodynamic Action and Diseases Caused by 



Light , Reinhold Publishing Corp., New York (19^+1) . 



(6) Spikes, J.D., and Ghiron, C.A., in press. International 



Symposium on Physical Processes in Radiation Biology , 

 Academic Press, New York. 



