PHENOLIC SUBSTANCES 207 



yiae results in the formation of both flavonols and anthocyanins of 

 monohydroxy or dihydroxy types. The allele C in the presence of the 

 dominant allele V, governs flavonols and anthocyanins mainly of the 

 type, 3'-4'-5'-trihydroxy, and C^ with V yields anthocyanins only, 

 these having the trihydroxy substitution in the B ring. This case rep- 

 resents an unusually complex form of interaction which Feenstra 

 interprets as indicating that a shift in the hydroxyl pattern of the B 

 ring to the trihydroxy configuration favors anthocyanin synthesis over 

 flavonol synthesis. 



Since it has already been established that the acetate and 

 shikimic acid pathways are involved in both anthocyanin and flavonol 

 synthesis, it is hardly surprising to find a number of instances of inter- 

 actions— in fact a number of expressions of this interaction— between 

 classes of flavonoids. Similarly, however, the total absence of a definite 

 instance of gene-controlled direct interconversion suggests that actual 

 interconversion of the classes of flavonoid pigments is not the rule. In 

 this connection it now appears that leucoanthocyanins, once thought 

 of as likely precursors to anthocyanins, do not function in this way. 

 Evidence is not unequivocal on this point, however. Genes affecting 

 leucoanthocyanins are known. In Impatiens a gene governs the 

 presence of a pelargonidin-type anthocyanin and, in addition, leuco- 

 pelargonidin (Alston and Hagen, 1955). Feenstra (1959) reported a 

 gene in Phaseolus governing the appearance of leucoanthocyanin. 

 The leucoanthocyanins, incidentally, provide some circumstantial 

 evidence favoring the position that methylation occurs at a late stage 

 in anthocyanin synthesis. Methylated leucoanthocyanins are prac- 

 tically unknown yet leucoanthocyanins are commonly found along 

 with methylated anthocyanins. 



The quantitative inheritance of flavonoids is provided with 

 some interesting illustrations. In some plants a rather large number 

 of genes may influence the amount of anthocyanin. In Primula, for 

 instance, at least four different loci contain dominant intensifiers for 

 anthocyanin, and five loci contain dominant inhibitors (de Winton 

 and Haldane, 1933). In Dahlia (Lawrence and Scott-Moncrieff, 1935) 

 two loci affect the amount of anthocyanin and two others affect the 

 amount of yellow flavonoid pigments. From studies of the physiology 

 of anthocyanin synthesis it is clear that a host of extrinsic factors can 

 modify anthocyanin content, in fact a number of generaUy harmful 

 influences actually bring about increased anthocyanin synthesis. It is 

 therefore to be expected that a large number of different genes would 

 achieve a similar effect through diverse means. From a systematic 

 viewpoint, gene homology between two factors which exert quantita- 

 tive effects on anthocyanin synthesis in two different species has a 



