CAROTENOIDS IN LAND PLANTS 



up. '^ ^ ^ As lycopene is by far the major pigment of commercial tomatoes, 

 the net effect of ** strong *' Hght might well be to reduce the total 

 amount of carotenoids synthesized. Further, there is some evidence 

 which suggests that shaded tomatoes, although physiologically unripe, 

 contain more carotenoids than do fruit fully exposed to the sun. ' * ^ 

 Here the important word is fully (probably connoting a high tempera- 

 ture), for the carotenoid content of oranges of the same age from the 

 same tree varies according to the aspect of the fruit. Those facing the 

 sun containing more than those facing away from the sun ; this 

 variation can even be observed on the opposite sides of the same 

 specimen. ^ ® ^ 



That ultra-violet light may also play a part in carotene formation is 

 suggested by the reports that tomato fruit produced in greenhouses and 

 thus less exposed to ultra-violet radiations than out-of-door plants, 

 contain less carotenoids than do those produced in the 

 open. 2 5. 20 9, 213-2 15 Ag is the case with visible light, ultra-violet 

 light inhibits carotenogenesis in the golden varieties. ^ ^ * Direct 

 ultra-violet irradiation of excised green commercial tomatoes, however, 

 retards the disappearance of chlorophyll and the appearance of 

 carotene, ^ » » whilst in excised mangoes ultra-violet light actually 

 increases the amount of carotenoids formed. ^ ° ^ 



(iii) Temperature. As early as 1913, Duggar ^ i ' noted that carotenoid 

 formation did not occur when unripe tomatoes were stored at 30°C. 

 This has recently been confini.ed by Went, Le Rosen, and Zech- 

 meister,2 04 McCoUum, ^ i « Ellis and Hamner^o^ and Sadana and 

 Ahmad. 2®* Ellis and Hamner found that green tomatoes held at 

 70°--80° F. failed to redden but became yellowish pink. Went et al. 

 and Sadana and Ahmad found that unripe tomatoes stored above 30° 

 failed to produce lycopene although formation of other carotenoids 

 was unimpaired {cf. Smith's ** light " experiments, p. 40). The 

 mechanism of lycopene production was not affected, however, because 

 on lowering the temperature the pigment soon appeared. A reasonably 

 sharp optimum temperature (19°C.) was observed for lycopene forma- 

 tion. McCollum confirmed that high temperatures do not favour 

 lycopene formation, and Sadana and Ahmad noted that carotene 

 production was greater at 34°C. than at 38°C. 



The carotenoid content of mangoes picked unripe increases on 

 ripening in store, i o 2, i o 3 ^s one would expect. The rate of formation 

 of these carotenoids is accelerated at high storage temperatures but it 

 is important to note the final amount synthesized is not affected by 

 temperature variations. ^ ^ ^ 



41 



