The Cytochromes of Plant Tissues 



483 



extract cytochrome c from plant tissues. The cytochrome c, extracted from 

 wheat embryos appeared to be identical with the cytochrome c extracted from 

 horse heart. More recently, Bonner and Smith (1961) and, independently, 

 Estabrook (this volume, p. 444) have shown that cytochrome c from wheat 

 germ has a low temperature absorption spectrum which is identical with that 

 of horse heart cytochrome c. Hagihara, Tagawa, Morikawa, Shin and 

 Okunuki (1959) have shown that the crystalline form of wheat germ cyto- 

 chrome c differs from that of cytochrome c from other sources. 



Table 1. Cytochromes b that have been described in plant tissues 



It has not been established definitely that plant tissues have a component 

 identical with cytochrome q of animal tissues. Martin and Morton (1957) 

 have used the term cytochrome c\ to describe an absorption band observed 

 in mitochondria of wheat roots and of silver-beet petioles. Cytochrome /, 

 which is in many respects rather similar to cytochrome c, was first described 

 and extracted by Hill and Scarisbrick (1951). The extraction procedure was 

 improved by Davenport and Hill (1952). Cytochrome/appears to be located 

 in the chloroplasts. Bendall and Hill (1956) have described a cytochrome 

 which is similar to /but not identical with it and which they have hesitated 

 to name. 



The a-components of plant tissues appear to be cytochromes a and a^. 

 Although the evidence is meagre, the few absorption spectra that are available 

 (see Chance and Hackett, 1959; Hackett and Haas, 1958; Yocum and 

 Hackett, 1957; Yocum and Bonner, unpubUshed work; Hartree, 1957; 

 Martin and Morton, 1957 and Bonner and Smith, 1961) makes it probable 

 that the cytochrome a -\- a^ band is identical with that found m heart 

 muscle and other sources. There have been many demonstrations of photo- 

 reversible carbon monoxide inhibition of a variety of plant tissues. As yet 

 there are no photochemical absorption spectra of carbon monoxide-inhibited 

 plant tissue respiration. 



