10 



PROBLEMS IN PHOTOSYNTHESIS 



to be some evidence in favour of a morphological picture of an organized 

 chlorophyll aggregate. We shall see in Chapter 4 that some investigators 

 consider such aggregates of great importance from a physiological point of 



view. 



In § 2 mention was made of the findings of Nishimura and Takamatsu 

 (28) regarding the /^-carotene-proteid. This compound has a molecular 

 weight of 5.7 X 10' and contains about 3000 /3-carotene molecules per 

 particle. 



§ 4. The Cytochrome Systems in Plants 



In chlorophyll-free plant material Bhagvat (3, 4) detected the presence of 

 the cytochromes a, b and c, doubtless performing the same functions as in 

 yeast and animal tissues. According to Hill and Scarisbrick (19, 34), the 

 green cells contain another hematin compound, which they called cytochrome 

 f, instead of cytochrome c. Davenport (8) found a cytochrome be in chloro- 

 plasts. As yet, a cytochrome oxidase specific to cytochrome f has not been 

 found. It is assumed that the very small quantities of cytochrome a in 

 chloroplasts are merely due to the surrounding tissues. The etiolated 

 yellow plastides of barley contains the cytochromes a, be and f. In Table 2 

 the results of these investigations are compiled. It seems that in the chloro- 

 plasts chlorophyll replaces cytochrome a in 500 to 1000 dmes higher quantities. 

 There is perhaps a lunctional relationship between the cytochromes and 

 photosynthesis. It is further assumed (9, 10, 25) that cytochrome f is oxidized 

 by light, so that the cytochrome system of the chloroplasts during illumination 

 acts like the cytochrome system of the mitochondria during respiration. No 

 oxidation of cytochrome f can take place in the dark because there is no 

 specific cytochrome oxidase.* 



Hill (18) pointed out that mitochondria and chloroplasts show some 

 resemblance with respect to the structure-bound cytochromes. The chloro- 

 phylls could be considered to be parts of these structures. It seems as if the 

 chloroplasts belong to the same category as the mitochondria, the a-component 

 of the cytochrome system being replaced by the chlorophylls. 



For literature on cytochromes in higher plants, see Hartree (17). 



