CAROTENOIDS IN PLANTS 



theoretically possible only if the structure of fucoxanthin is as he 

 suggests (see p. 132). The mechanism would then be : 



V_^Me +H20 V_y_Me +0 V_y_Me 



Me Me Me 



SEXUAL FUNCTION AND CAROTENOIDS 



The differential distribution of carotenoids in the sex organs of 

 many algae has already been noted, (see p. 134). Heilbron ^ ^ 4 suggests 

 that ^-carotene, the pigment in the male gametes of Fucus serratus and 

 F. vesiculosuSy may control the motility of the spermatozoa. Under 

 the stimulus of light and in the presence of oxygen and a specific 

 enzyme ^-carotene may be converted into crocetin dimethylester which 

 could then function as a gamete stimulator. ^ * 



It was noted in 1938 by Kuhn, Moewus and Jerchepo^ that washed 

 cells of the unicellular flagellate Chlamydomonas eugametos became motile 

 when either exposed to light, or kept in the dark but supplemented 

 with sugar and oxygen, or kept in the dark and treated with filtrates 

 of motile cells. Addition of larger amounts of filtrates which had been 

 exposed to light for a short period stimulated the formation of female 

 gametes ; if the filtrates were exposed for longer periods before addi- 

 tion, male gametes were formed. The essential step was irradiation, 

 for non-irradiated filtrates were completely inactive. It eventually 

 transpired that similar differential gametogenesis could be brought 

 about by the addition of appropriate mixtures of labile (cis-) and stable 

 (trans-) forms of crocetin dimethylester. A 3 : 1 mixture of the cis- 

 and the trans- forms stimulated female and a 1 : 3 mixture stimulated 

 male gametogenesis. ^ ^ * As m-crocetin can be converted into the 

 trans- form by irradiation, it is concluded that these isomers are the 

 substances produced by irradiating ..the Chlamydomonas cell filtrates. 

 The photolabile precursor of crocetin has not yet been identified but 

 the structure of crocetin indicates that theoretically it could be formed 

 by the degradation of a C40 carotenoid. 



Crocetin has not been dealt with in detail in this book which is 

 primarily concerned with C40 carotenoids (i.e.y those containing 8 



147 



