CAROTENOIDS 



Neo-p-carotene U 



Me 



Neo-p-carotene B 



(v) Colourless polyenes. Recently attention has been turned to the 

 colourless fluorescing and non-fluorescing unsaponifiable compounds 

 which accompany carotenoids in fruits. These substances, which 

 are dealt with in detail later, are carotenoids in which varying num- 

 bers of double bonds have been saturated. They have not usually 

 been considered to occur in green tissues but recently Porter and 

 Burns** have reported the presence of tetrahydrophytoene (? eicosa- 

 hydrolycopene) in leaves. 



Some phylogenetic relationships based on the carotene distribution 

 in leaves have been suggested by Mackinney * ; the safest generaliza- 

 tion which appears justified is that if one member of a family contains 

 no a-carotene, then it is unlikely that other members will do so. The 

 amount of a-carotene in any plant can be forecast with some degree of 

 accuracy, but no explanation is yet available of the sporadic appearance 

 of this carotenoid. Table 1 summarizes data on the carotenes of green 

 leaves. 



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