145 



Ellen C. Weaver and Norman I. Bishop 



HT OFF 



OXYGEN MUTANT NO. 1 1 



T OFF 



0.5 sec FLASH 



=^^ 525 m/i 



TOTAL PERIOD 4 SECONDS 



I I I I I 1 1 



0.5 sec - 



Fig. 7 Absorption changes in Mutant 11 with flashes of different 



duration. Each curve is the s'uramation of 50 repetitions 

 of the k second light-dark cycle. 



De-adaptation at high light Intensities is prevented by the ad- 

 dition of 3(3,4-dichlorophenyl)-l-l-dimethylurea (DCMJ) to prevent 

 the evolution of oxygen. Scenedesmus thus treated "behaves very 

 much like untreated Mutant 11 in its capacity for photoreduc- 

 tion(9); it was therefore not unexpected that the adapted wild 

 type should display the 525 ni|a ahsorption shift with kinetics re- 

 sembling those of Mutant 11, as can be seen in Fig. 8. 



We are still not able to equate any of the spectral shifts in 

 the region we have been examining, i.e. that between 3^0 mji and 

 580 m|j,, with either of the typical free radical signals. The pre- 

 sence or absence of characteristic EPR signals may in general be 

 correlated with the photochemical behavior of the mutant; however, 

 the rapid kinetics of the formation and decay of these signals in 

 the mutants has not yet been studied. It is notable that all the 

 major absorption changes appeared in each strain, whether or not 

 metabolic activity was occurring. The kinetics of these changes 

 were strikingly altered in the mutant cultures, and it is hoped 

 that further study will provide a basis for explanation of these 

 time course differences, and perhaps yet reveal underlying rela- 

 tionships between observations by these two differing experimen- 

 tal techniques. 



