PHOTOSYNTHETIC PIGMENTS 



31 



the oxidation of carotenoids. It has also been suggested — 

 particularly in certain algae — that some of the carotenoid 

 pigments are combined with protein in the cell. The brown 

 algae turn green on heating owing to an alteration in the 

 state of the fucoxanthol. It is clear that many aspects of 

 carotenoid biochemistry remain to be explored. 



The absorption of light by carotenoids 



All carotenoids strongly absorb light in the violet end of 

 the visible spectrum, showing two or three separate bands 



^00 ^50 ^OOmf 



Wavelength of light 



FIG. 3.4. Absorption curve for typical carotenoids; luteol (- 



zeaxanthol ( ) dissolved in ethanol. (Data of 



Zscheile et al.) 



(Fig. 3.4). The absorption extends into the blue to different 

 extents according to the structure of the compound. The 

 carotenoids of the bacteria absorb further to the red than 

 those of higher plants. Even more than in the case of the 



