CAROTENOIDS IN PLANTS 



less abundant, other xanthophylls which occur in the higher plants, 

 however, occur rarely in algae and then only in traces ; some investi- 

 gators claiming that they never occur. Instead, new and specific 

 xanthophylls are generally found. Of these, when the algal distribution 

 over the world's surface is considered, fucoxanthin is probably the 

 most abundant naturally-occurring carotenoid. 



When the relative amounts of carotenes and xanthophylls in the 

 vegetative regions of the plants are considered, there are no well-marked 

 differences between the higher plants and the algae and no single 

 value can be cited as characteristic of either group. The usual xantho- 

 phylls : carotenes ratio for higher land plants varies from 4 to 9 with 

 a value of perhaps 15 for some alpine plants. These values are typical 

 of those found for algae. Ratios between 5 and (.?) 50 were obtained 

 for 12 green fresh water algae, between 3-4 and 8-3 for fresh water 

 Rhodophyceae varying in colour from green to reddish brown, and 5-4, 

 6-0 and 1 1 -4 for 3 flagellates. ^ ' » 



Formation 



(i) Ejfect of Carbon and Nitrogen Sources 



As in the case of higher plants very little is known of carotenoid 

 formation in algae. Interesting contributions have come from Chodat^'^ 

 and Chodat and Haag, ^ ' ^ who consider carotenogenesis to be of two 

 types : 



[a) spontaneous carotenogenesis arising during grovi^h on a normal 

 medium owing to the genetical disposition of the algae. 



{b) excessive carotenogenesis induced by the medium owing to 

 carbon-nitrogen imbalance. 

 Chodat argues that if nitrogen is in excess all (or most) of the carbon 

 is used up in protein synthesis and there is none available for fat and 

 carotenoid synthesis. On the other hand if carbon is in excess, there is 

 plenty to spare for fat and carotenoid synthesis. Adequate proof of 

 this interesting hypothesis is yet to be presented, but it should be 

 noted that in fungi it is the amount of assimilable carbon which is the 

 controlling factor, the C/N ratio having only limited significance, i ». a o 

 In this connection Lwoff and LwoflF^^^ have shown that carotenoid 

 synthesis by Haematococcus pluvialisy growing on a medium containing 

 asparagine or peptone, is stimulated" by the addition of sodium acetate 

 although it is independent of its concentration in the medium. 



More recently Wenzinger^'^ has shown that carotenoid synthesis 

 in Dictyococcus cinnabarinus is much increased when the nitrogen 

 source [Ca(N03)2] is reduced by one third, i.e., when the C/N ratio 

 is increased ; unfortunately, iron which is needed by this alga for 



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