CAROTENOIDS IN PLANTS 



in algal carotenoids but apart from the pioneer work of Kylin^^* a 

 considerable amount of the detailed knowledge has come from Heil- 

 bron's laboratories. Comprehensive reviews of algal pigments have 

 been published by Heilbron himself^ ^^ and his colleague A. H. 

 Cook. 1 2 6 These have been of considerable value in compiling this 

 section. From the point of view of this book it is considered better 

 to discuss the carotenoids according to the general classification 

 described by Fritsch, ^ ^ ' rather than to discuss fresh water and marine 

 algae separately. Little is gained by adopting the latter procedure. 



Chlorophyceae 



The green algae resemble biochemically the green leaves of higher 

 plants much more closely than do any other class of algae. Carter, 

 Heilbron and Lythgoe^'^^ found ^-carotene and lutein (xanthophyll) 

 to be the predominating carotenoids. Kylin^^* found the same dis- 

 tribution in Enteromorpha intestinalis, E. compressa and Cladophora 

 rupestrisy and Oedogonium spp. 1 2 4, 1 2 9. small amounts of oL-carotene^o^rt 

 also occasionally encountered. The same distribution also exists in 

 Cladophora glomerata^^^. The xanthophylls accompanying lutein 

 (xanthophyll) are probably not so varied as those associated with 

 lutein in the higher plants, but violaxanthin has been found in E. 

 intesttnalis, C. rupestris, ^ ^ » C. glomerata ^ ^ ^ and Vaucheria hamata ; ^ ^ ^ 

 zeaxanthin in E. intestinalis and C rupestris^^^ and taraxanthin 

 in Cladophora sauteriy Nitella opaca, and Oedogonium species. ^ ^ ^ 

 Luetin-5 : 6-epoxide occurs in Cladophora glomerata. ^ ^ " 



A number of Chlorophyceae depart from this general picture. Trente- 

 pohlia aurea yields a single pigment only, first noted as haematochrome 

 by Cohn^^2 in 1861, which is now known to be [3-carotene ; 126.133 

 this alga is one of the richest sources of p-carotene known for it 

 comprises 0-2 per cent, of the dry weight as compared with about 0-05 

 per cent, of the dry weight of leaves of higher plants. Haematococcus 

 pluvialis is an even more interesting exception for it contains astaxan- 

 thin, 1 3 * hitherto considered a characteristic carotenoid of invertebrates, 

 especially Crustacea {see p. 168) ; this pigment was originally termed 

 euglenarhodone ^ ^ ^. Three astaxathin esters occur in H. pluvialis two 

 mono- and one di-esters. The fatty acid associated with the di-ester and 

 one of the mono-esters has an empirical formula CieHgoOa, and that 

 with the other ester C18H34O2 ; a- and p-carotene and lutein are also 

 present. Astaxanthin has also been found, together with [3-carotene, 

 in Protosiphon hotryoides and Brachiomonas simplex. ^ ^ • The presence 

 of fucoxanthin in Zygnema pectinatum ^ ^ 6 js extremely surprising and 

 may be due to contamination by diatoms, of which group fucoxanthin 



129 



