PART I 

 CAROTENOIDS IN PLANTS 



CHAPTER II 

 CAROTENOIDS IN LAND PLANTS 



I. Phanerogams 



Carotenoids are found in all green tissues of plants, and their 

 occurrence and distribution in these tissues will be our first con- 

 sideration. 



LEAF CAROTENOIDS 

 Carotenes 



(i) ^-carotene. The leaf carotenoids are associated with chlorophyll 

 in the chloroplasts i' ", probably as water-soluble protein complexes* 

 but occasionally as lipid droplets. * The intense green of the chloro- 

 phyll components normally masks the orange-yellow of the carotenoids. 

 It is only during early autumn, when the chlorophyll is destroyed and 

 the leaves yellow, that the carotenoids become apparent to the naked 

 eye. In the dying leaf the carotenoids themselves undergo changes 

 which will be discussed later {see p. 19). The final bronze and red 

 colours observed in falling leaves are not due to carotenoids but to 

 water-soluble pigments not yet fully identified. 



As soon as the implications of the classical researches of Tswett* 

 on the chromatographic separation of the lipid-soluble plant pigments 

 were fully appreciated, developments in the isolation and chemical 

 characterization of the carotenoids were extremely rapid. The out- 

 standing work of Karrer and of Kuhn and their collaborators on the 

 elucidation of the structure of the carotenoids has recently been fully 

 and authoritatively discussed by Karrer and Jucker. * The most 

 common carotene found in green leaves is ^-carotene, in fact it is 

 probably true to say that all leaves contain this pigment. The one 

 report to the contrary which claimed that the green leaves of the 

 Formosa tea plant contain exclusively a-carotene' has now been 

 refuted. * 



In the largest single investigation so far reported, Mackinney* 

 identified p-carotene in 59 different species. The concentration of 



