CAROTENOIDS IN PLANTS 



{see p. 158). Closer investigation of the fresh water Peridinium cinctum 

 has revealed the presence of two further xanthophylls, diadinoxanthin 

 {see p. 131) and a specific pigment dinoxanthin, very similar in properties 

 to violaxanthin. Three isomers, neoperidinin (neosulcatoxanthin ?), 

 neodiadinoxanthin and neodinoxanthin, were also detected but may 

 possibly be artefacts. ^ * * 



According to Scheer^'^ Prorocentrum micans contains about 0-025 

 per cent, of carotenoids (dry weight) of which about 10 per cent, is 

 carotene. 



Chloromonadineae 



Little is known about the carotenoids which occur in this small 

 class of fresh water algae. Fritsch ^ ^ ' states that the bright green tint 

 of their discoid chromatophores is due to an excess of " xanthophyll " 

 and Cook^"* notes that "colour tests" indicate the presence of 

 xanthophylls. 



EUGLENINEAE 



The carotenoids of this class are located in the stigma or eye spot. 

 Kylin^** noted 3 modifications of " red haematochrome " in Euglena 

 species, ^-carotene, lutein (xanthophyll) and zeaxanthin are probably 

 present but the main pigment is that isolated by Tischer ^ • ^ which he 

 called euglenarhodone. Recently Kuhn, Stene and Sorensen, ^ * * and 

 Tischer himself, ^ ^ * have proved the identity of euglenarhodone and 

 astaxanthin {see p. 170). This discovery of astaxanthin in plants is most 

 striking, (it has also been noted in H. pluvialis) for until recently it 

 had been considered the typical marine animal carotenoid. This well 

 emphasises the fact that the flagellates, to quote Heilbron, ^^s <« bridge 

 the gap between the vegetable and the animal kingdom." Heilbron has 

 little doubt that the pigment which is located in the eye spots ^ « ^ of 

 nearly all the motile cells of the flagellates will turn out to be astaxan- 

 thin. 



Cyanophyceae (Myxophyceae) 



In 1843 Kraus and Millardet^** were first to note the presence of a 

 carotenoid in this group and called it phycoxanthin. Thirty years later 

 Kraus ^ • ' claimed that it was not identical with any carotenoid of the 

 higher plants. Sorby ^ « « confirmed this but also found carotene present. 

 The first modem investigation into an alga of this class was carried 

 out on Calothrix scopulorum by Kylini24. apart from carotene he 

 separated three other pigments, myxorhodin-oLy myxorhodin-ftt and 



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