737 



Cyanide protected algal Hill reaction significantly from gamma 

 radiation damage^ while beta-aminoethylisothiuronium hydrobromide 

 (AET) had no protective effect. Both light and oxygen protected 



J 



John D. Spikes and Dennis C. Hall 



As may be seen^ the Hill reaction activity fell off progressively 

 with increasing dye concentration in the photodynamic experi- 

 mentS; whereas little inactivation occurred if the algae were 

 kept in the dark. In the case of photosynthesis, activity fell 

 off rapidly with increasing dye concentration in both the light 

 and in the dark; activity was lost more rapidly in the light. 

 The algae treated photodynamic ally in the presence of high con- 

 centrations of dye actually took up oxygen on illiomination in the 

 photosynthetic system. 



Ultraviolet effects on Hill reaction and photosynthesis - 



Space permits the presentation of only a few observations on 

 the comparative effects of 2537 A ultraviolet radiation on algal 

 Hill reaction and photosynthesis. V/hen the algae were irradiated 

 at a dose rate of I36O microwatts/cm^, the photosynthetic rate 

 dropped to 50^ after 3 nun. and to zero after 5 min. In con- 

 trast, the Hill reaction rate increased sharply at first and 

 attained a value 2Vfo greater than that of the control after one 

 min. of irradiation. The activity then decreased rapidly with 

 dose, and dropped to ^QFJo after h min. and to zero at 5 min. 

 After the transitory initial rise, the time-course for loss of 

 Hill reaction activity closely resembled that for the loss of 

 photosynthetic activity. In neither case did the loss of acti- 

 vity follow first-order kinetics. Algae irradiated for 6 min. 

 or longer took up oxygen on illumination at a rate 15-20 times 

 greater than the rate of uptake in the dark. No photoreacti- 

 vation of the Hill reaction or photosynthetic activity in ultra- 

 violet-irradiated algae was observed. 



Gamma radiation effects on Hill reaction and photosynthesis - 



Again, space permits the presentation of only a few highlights 

 in this area of work. The loss of both Hill reaction and photo- 

 synthetic activities v^as approximately linear with gamma radi- 

 ation dose. Loss of activity was greater at higher irradiation 

 temperatures; the loss of Hill reaction activity was more 

 temperature- dependent than the loss of photosynthetic activity. 

 At 12°C. the Hill reaction fell off more rapidly with increasing 

 dose (50^ inactivation at 550^000 rad) than did photosynthetic 

 activity (50/0 inactivation at 790,000 rad). | 



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