The Cvtochromes of Plant Tissues 



493 



the same cytochrome components as found in cyanide-sensitive plant tissues. 

 A series of spectra of a particulate preparation from skunk cabbage is shown 

 in Fig. 9. Such particulate preparations are hardly affected in their rate of 

 oxidation of succinate by sodium azide in concentrations as high as 0-01 m. 

 It may be seen that the cytochrome spectrum does not differ in any way from 



Fig. 13. Difference spectra (at — 190°C) obtained from a black valentine bean root 



particulate preparation. The spectra represent the difference in absorption 



between aerated particulated suspensions and suspensions reduced with dithionite 



(solid line) and DPNH (dashed line). 



that of cauliflower mitochondria (Fig. 5) which are inhibited fully by rela- 

 tively small concentrations of sodium azide. 



DISCUSSION 



In the preceding section a large number of absorption spectra have been 

 presented and now one may well ask what positive contributions to our 

 understanding of plant cytochromes have been made here. How far can one 

 go in delineating the cytochromes of plant tissues? Which specific com- 

 ponents are involved in electron transport to oxygen and in the photo- 

 synthetic apparatus? What are the immediate problems that now face us? 

 These are important questions and most of the answers are not immediately 

 apparent. 



We now have available considerable lore relating to the cytochrome 

 components of plant tissues and this paper adds to this. However, the 

 results presented in this study of plant cytochromes show quite clearly that, 

 in spite of the complexity of the problem, there is an undercurrent of unity. 

 It has been shown here that plant tissues appear to contain some of the same 

 cytochrome components and these components are unique to plants. In 



