CHAPTER III 



FORMATION AND FUNCTION OF CAROTENOIDS IN 

 PHANEROGAMS 



THEORIES OF FORMATION 



The site of formation of carotenoids in plant cells is by no means 

 certain. Weinzinger^ has investigated this from the cytological view- 

 point but has produced no overwhelming evidence in favour of forma- 

 tion either in the chondriosomes or in the plastids. A point he does 

 make which requires re-emphasis is that there is no a priori reason to 

 assume that the site of accumulation of carotenoids is also the site of 

 their formation. Assumptions of this type of reasoning misled for 

 many years workers studying the conversion of p-carotene into vitamin 

 A (see p. 275). 



Me 



CH 



Me Et 



Me 



CH 



CHO Et 



CH 



CH 



Mg 



/ 



r\ 



J 



CH 



\ 



K^ 



CH 



CH 



Mg 



i^ 



CH 



CH^ 

 I 

 C20H39OOC 



l/\ 



COOCHj 



Me 



r 



CH 



Me "cH 



CH 



C20H39OOC 



COOCH3 



N 



Me 



Chlorophyll A 

 CH, 



CH, 



Chlorophyll B 

 CH3 



CH3.CH.CH2.CH2.CH2.CH.CH2.CH2.CH^.CH.CH2.CH2.CH^.C = CHjCHj0H 

 Phytol 



As long ago as 1837 Berzelius, ^ who first extracted carotenoids from 

 autunm leaves, considered that these pigments were breakdown 

 products of chlorophylls, although in 1838 he found that they also 

 occurred in green leaves. This suggestion has influenced the thoughts 

 of many later scientists in their search for a theory of carotenoid 

 formation in plants. More specifically Willstatter and Mieg ^ suggested 



63 



