87 



Walter Bonner and Robert Hill 



plasts. No light induced oxidations or reductions of cytochrome 

 b^ were found In whole chloroplasts or in green leaves. 



Having learned the technique of observing light induced 

 optical changes in partially greened leaves, it was relatively 

 simple to record light induced cytochrome f^ oxidation in a large 

 variety of fully greened leaves, in green algae ( Chlorella , 

 Chlamydomonas ) and in blue-green algae. The light activated 

 spectral responses in a fully green spinach leaf are shown in 

 Figure 5 where again the characteristic assymetric a-band of 

 cytochrome f^ is strikingly apparent, but unlike the partially 

 greened mung bean leaf, the fully greened leaf shows the response 

 at 518 m^.. There is no 518 m|j. response in Euglena graciles or in 

 Anacystis nidulans , an observation in confirmation of Olson and 

 Smillie (this symposium) and of Amesz and Duysens (10), 



Light Induced Responitt 

 Spinach Ltaf 



T 



AOD -0005 



_L 



1 1 1 1 



510 520 530 540 550 560 m^ 



Fig, 5 The light activated optical responses of a fully green 

 mature spinach leaf plotted as a function of wave length. 



It is shown in another paper (Chance and Bonner, this 

 symposium) that the light induced oxidation of cytochrome f^ 

 proceeds at 77° K and the oxidation rate is more rapid at this 

 temperature than at 25° C. Even so, the "on" and "off" responses 

 of the partially greened be^n leaves are remarkably fast at 25oC. 

 The partially greened leaf has the terrific virtue that in the 

 kinds of experiments described here there is a negligible effect 

 of the measuring light on the cytochrome f_ response, a situation 

 that depends on the low chlorophyll concentration and hence the 

 high light intensity requirement and one that does not exist in 

 fully greened tissues or cells. The "on" and "off" responses for 



