89 



Walter Bonner and Robert Hill 



ment for cytochrome f_ oxidation, a requirement that negates 

 possible influences of the measuring light, and (c) the control of 

 the development of light activated responses through control of 

 the leaf chlorophyll content. 



The observation that light-induced cytochrome £ oxidation 

 can be observed after an etiolated leaf has been allowed to forr> 

 some chlorophyll is simply a prelude to the observations that 

 now must follow. What is the role of cytochrome b^, does it form 

 a complex with chlorophyll, is it oxidized or reduced by light, 

 or does it have any role in photosynthetic electron transport? 

 Very precise data are now needed on rates of chlorophyll forma- 

 tion, development of the f^ response, development of oxygen evolu- 

 tion and carbon dioxide assimilation, plastoquinone formation, the 

 time relations involved in the 518 response as well as correla- 

 tions of the above lore with the light-induced completion of the 

 chloroplast structure itself. Preliminary experiments have shown 

 that many hours of greening are required before plastoquinone is 

 formed. Because of the close association, in the minds of various 

 investigators, between plastosquinone and the 518 response, it is 

 very important to follow the development of this response during 

 greening. It is always a pleasure, however, to find that the 

 solution of a specific problem points immediately to other 

 specific and more challenging problems. 



SUMMARY 



1. Cytochromes f_ and b^ can be observed directly, by means 

 of a microspectroscope, in intact leaves of dark grown mung bean 

 seedlings. Spectra of these same cytochromes can be obtained 

 from plastid suspensions prepared from such etiolated leaf tissue, 



2. Following the development of a small amount of chloro- 

 phyll in the mung bean leaves, and while cytochrome b^ is still 

 visible in the microspectroscope, the absorption spectrum of cyto- 

 chrome f_ can be plotted from the light activated optical responses 

 as observed in a differential spectrophotometer, 



3. Following more prolonged greening the a-band of cyto- 

 chrome b5, as observed visually, remains sharp but gradually 

 disappears without noticeable change in the position of its 

 maximum, 



4. The absorption spectrum of cytochrome f^ can be plotted 

 from the light activated optical responses, as observed in the 

 differential spectrophotometer, in a variety of fully greened 

 leaves and in green algae, 



5. No light-induced optical responses corresponding to cyto- 



