CAROTENOIDS IN LAND PLANTS 



Table 2 indicates the xanthophylls isolated by Strain and the relative 

 amounts of each obtained ; data reported subsequent to Strain's 

 investigation are also included. Strain resolved mixtures I, II, and III 

 (Table 2) into a number of components by further chromatography 

 on CaCOg and povi^dered sucrose. None of these components was 

 isolated or identified, although it seems unlikely that they were all 

 oxidative artefacts. 



The flavoxanthins are designated b and c and violaxanthin, 6, to 

 distinguish them from the pigments isolated by Kuhn and his colla- 

 borators from flower petals (see p. 46) ; these pigments differ from 

 Kuhn's pigments in chromatographic behaviour, m.p. and in optical 

 rotations but are spectroscopically indistinguishable. Whether they 

 are the separate pigments which Strain *^'®<> considers them is still 

 doubtful. Assuming for the moment that they are not identical they 

 must be very closely related to the corresponding flower pigments. 



It is only recently that the structures of violaxanthin and flavoxan- 

 thin have been determined, although their empirical formulae have 

 been known since 1931-2. ^^^^ Karrer's school working on the 

 oxidation of carotenoids discovered that those members containing a 

 p-ionone residue could be oxidized to 5 : 6-expoxides by treatment 



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15 



