CHAPTER II 



The formation of carotenoids in plants and 

 their physiological significance 



I. MODE OF FORMATION 



No experimental evidence, only hypotheses, exist at present with regard 

 to the mode of formation of carotenoids in plants. It therefore appears prema- 

 ture to come to any definite conclusions on this subject. 



Karrer, Helfenstein, Wehrli and Wettstein^ consider the possibility 

 that lycopene may be formed from phytyl aldehyde by a benzoin condensation 

 or by a pinacol reduction, followed by dehydrogenation. 



Carotenoids containing fewer than 40 carbon atoms in the molecule may be 

 formed by oxidation of C^^ carotenoids^. 



Several investigations have been made concerning the morphological 

 changes which take place in fruit during the ripening process. Some of these 

 are referred to on p. iig^. 



2. THE FUNCTION OF CAROTENOIDS IN PLANTS 



Although numerous investigations have been carried out within recent 

 years concerning the significance of carotenoids in the vegetable organism, our 

 present knowledge of this subject is still very scanty and no final opinion can 

 be formed. The first studies in this field by Willstatter and his school* 

 attempted to demonstrate a possible influence of carotenoids on the processes 

 of respiration and assimilation, but with negative results. More recently a 

 number of workers have sought to determine the influence of carotenoids on 

 sexual reproduction. The following is a brief summary of the results so far 

 obtained. For details the original literature should be consulted. 



Willstatter and Stoll^ examined the function of carotene and xantho- 

 phyll in green leaves, in which the two carotenoids occur in fairly constant 

 proportion to chlorophyll. They were unable to detect any definite influence 

 of the two pigments on respiration. According to Noack^, carotene and xantho- 

 phyll fulfil the role of light filters for chlorophyll, whereas Went^ has expressed 

 References p. ly-ig. 



