CAROTENOIDS 



the rate of carotenoid formation increases more quickly than does the 

 development of the leaf. It has recently been shown that the carotene 

 content of the crosses of yellow dent maize is always significantly 

 related to the content of the parent strain. ^^^^ 



Randolph and Hand^'*^ studied the carotenoid content of pure 

 yellow diploid maize carrying the three dominant genes YYY for 

 yellow, and a derived tetraploid with double the number of genes, 

 YYYYYYy for yellow. Doubling the number of chromosomes in- 

 creased the carotene content of the maize by 40 per cent. Each carotenoid 

 was increased to the same extent. This increase combined with the 

 increased endosperm cell volume in the tetraploids (3-6 times) resulted 

 in a five-fold increase in the amount of carotenoid per cell. It is con- 

 sidered that this increase is due to a cumulative action of the dominant 

 genes for yellow endosperm colour, the amount of carotenoid 

 elaborated per gene in the tetraploid being 2-5 times as great as that 

 produced per gene in the diploid. On the other hand, doubling the 

 number of chromosomes in white maize resulted in a decrease of 19 

 per cent, in carotenoid content, there being no cumulative gene action 

 in this case. A somewhat similar investigation by Brunson and Peter- 

 son^ ^* showed that in maize there was a straight line relationship 

 between carotene and zeaxanthin concentration and gene dosage. 

 They confirmed a slight but consistent cumulative tendency with higher 

 gene doses ; this action was most marked in the zeaxanthin fraction. 



Webster, Brookes and Cross ^^^^ record a carotene content of 

 0-0192-0-0226 mg/g. for open-pollinated corn and 0-0170-0-0199 

 mg/g. for hybrids ; these differences are considered significant. 



There is no such increase in the carotenoid content of tetraploid 

 rye, ^ ^ * barley, ^ ^ ^ and some other plants, ^ ^ ' compared with diploid 

 types, although an increase has been reported in tetraploid wheat. ^ ' ' 



In tomatoes there are three gene pairs controlling coloration, Rr, 

 Tty and Yy. Rr control the formation of lycopene and to a less 

 extent carotene and the xanthophylls, ^ ^ ® whilst T and t determine the 

 spatial configuration of the carotenoids (principally lycopene) ; for 

 example, the dominant T controls the production of all-/raw-lycopene 

 and the recessive t the production of poly-m-lycopenes.^ ^ ^ The geno- 

 types of the red, yellow and tangerine tomatoes are thus considered to 

 be, respectively, RRTT, RRTt, and RRtt^^^ Recent work has led 

 Mackinney and Jenkins ^ * ^ to develop this idea and to conclude that 

 in the absence of i?, T is responsible for lycopene production only on 

 a limited scale, whilst in the absence of J", R is responsible for large 

 amounts of t^-carotene, prolycopene and protetrahydrolycopene (poly- 

 os-carotene). The outstanding work of Porter and Lincoln^ ^ on cross- 



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