83 



Walter Bonner and Robert Hill 



that in certain selected algal mutants it is possible to make 

 direct observations on the chloroplast cytochromes (8) and Indeed 

 in one of them, to show light induced oxidations of cytochrome f^ 

 and of a b-type cytochrome (8,9). The small etiolated leaves of 

 mung bean seedlings show intense bands of both plastid cyto- 

 chromes when the leaves are observed through a direct vision micro- 

 spectroscope. Furthermore, it is possible to record a spectrum 

 of the two cytochromes in a suspension of plastids prepared from 

 etiolated mung bean leaves. Figure 1 shows such a spectrum. 



— I 1 1 1 r 



510 530 550 570 590 



Fig, 1 Low temperature (77°K) difference spectrum, reduced- 

 oxidized, of a suspension of plastids isolated from etiolated 

 mung bean leaves. 



The small etiolated mung bean leaves, minus their mid-ribs 

 could be relatively easily layered on a special rack which 

 fitted into the moist chamber and which in turn, fitted into the 

 optical path of the double-beam differential spectrophotometer. 

 Both of the authors are deeply indebted to Dr. Hiroshi Ikuma who 

 possesses great skill in the delicate operation of mung bean leaf 

 mounting. 



No light induced optical changes could be observed in the 

 etiolated leaves, in the region between 500 and 580 mn, until the 

 leaves had been allowed to produce some chlorophyll. Greening of 

 the leaves was accomplished by illuminating them, in the moist 

 chamber, with lov? intensity red light. The filter used for green- 



