PHOTOSYNTHETIC PIGMENTS 



37 



of respiration/cytochrome c in yeast approximates to the 

 ratio of rate of photosynthesis/cytochrome / in leaves, both 

 rates being expressed as Qo^. 



THE STATE OF THE PIGMENTS IN THE PLASTID 



The phycobilins are as we have seen water soluble 

 chromo-proteins whilst chlorophyll and the carotenoids are 

 soluble only in organic solvents. Thus we are led to postu- 



400 



480 560 640 



Wavelength of light 



720 m/^ 



FIG. 



3.6. Comparison of the absorption spectrum of a suspension 



of Chlorella cells ( ) and that from the combination 



of the spectra of the isolated pigments in solution ( ). 



(After Emerson and Lewis.) Maxima for absorption in the red 

 made to coincide. 



late at least a two-phase system within the chloroplast. In 

 gross composition the plastids are 50% water, 25% protein, 

 15% lipoid, and about 10% pigment. As to the detailed 

 chemical structure and organization of the plastid there is 

 little direct evidence. 



The association of the pigments with other constituents of 

 the plastid is shown by the difference in the position of the 

 maxima of the absorption bands of the pigments in the plant 

 cell compared with that of the pigments in organic solution. 



