140 On, the Formation of Anthocyanin 



The mustard oil glucosides, sinigrin and sinalbin, occurring in 

 mustard and other Cruciferae, also give products with a characteristic 

 odour of mustard oil on hydrolysis : — 



C,„H,eOsNS,K + H,0 = C3H5CNS + CeHiA + KHSO, 



sinigrin allyl sulpho-cyanide 



The hydrolysis of glucosides on autolysis in chloroform or through 

 injury, can also be detected when the non-sugar component of the 

 glucoside molecule is an aromatic substance, which when free from 

 glucose is subsequently oxidised to a coloured compound through the 

 agency of an oxidising enzyme (oxidase); in this case the development 

 of colour indicates the progress of the reaction. 



In some genera the pigments produced in this way after death or 

 injury to the plant are red, purple or blue, and hence attention has 

 been di'awn to the phenomenon, and the products so formed have been 

 used commercially for dyeing purposes. The best known examples are 

 the " indigo plants," Indigofera spp., Isatis tinctoria, Polygonum, 

 tinctorium, etc. 



The processes taking place in the formation of indigo have been 

 very fully investigated and can be expressed as follows: — 



Ci,Hi70eN + H,0 = QHiA + CsH.ON 



indicau glucose indoxyl 



2C8H,ON + 0, = 2H,0 + CaaH,„0,N, 



indigotin 



The first reaction is brought about by a glucoside-splitting enzyme, 

 indimulsin, which hydrolyses the glucoside, indican ; the second by an 

 oxidase which oxidises the colourless indoxyl to the pigment indigotin 

 or indigo. 



Another striking example is the rapid formation of a bright 

 red pigment in the flowers and leaves of Schenkia blumenaviana on 

 autolysis in chloroform as described by Molisch(lO). 



Though the formation of a brightly coloured pigment after death 

 is a comparatively rare phenomenon, yet many plants rapidly turn 

 brown or reddish-brown when placed in chloroform vapour. The 

 same effect is produced by mechanical injury and sometimes by 

 immersion in absolute alcohol (Mirnbilis Jalapa). Extracts from such 

 plants give a blue colour with guaiacum tincture and there is little 

 doubt that the production of pigment is due to the oxidation of an 

 aromatic substance through the activity of the oxidase. 



