THE BIOSYNTHESIS OF CYANOGENIC GLUCOSIDES IN ROOTS OF CASSAVA

Linamarin is the main cyanogenic glucoside of cassava. De novo synthesis of linamarin in cassava roots was demonstrated in vivo by feeding [C-14]valine to excited segments of phelloderm. In vitro, a microsomal enzyme system isolated from cassava roots was shown to catalyse the conversion of valine to acetone cyanohydrin, the aglucone of linamarin. An antibody raised against cytochrome P450(TYR),the enzyme which catalyses the initial step in the biosynthesis of the cyanogenic glucoside dhurrin in sorghum, cross-reacts with a major polypeptide of similar molecular mass in cassava microsomes. Cyanogenic glucosides are known to accumulate in cassava roots, but hitherto de novo synthesis has only been demonstrated in the leaves, suggesting translocation of cyanogenic glucosides from leaves to roots. Our results show that at least part of the cyanogenic glucosides are synthesized in the roots. The data demonstrate that acyanogenic cassava roots cannot be obtained solely by blocking the transport of cyanogenic glucosides to the roots from other parts of the cassava plant.