Differential biosynthesis and transport of linamarin in high and low cyanide cultivars of cassava (Manihot esculenta)
1993
McMahon, J.M. | Sayre, R.T.
Cassava varieties can be subdivided into low and high cyanide groups, based upon the linamarin content in the roots. It is generally assumed that differential rates of linamarin synthesis in leaves account for the varietal differences in root linamarin content, however steady-state concentration in leaves of low and high-cyanide cultivars are identical. In order to account for the differential accumulation of linamarin in roots, 14C-valine, the precursor to linamarin, was fed to leaf blades of low (HMC-1) and high (CM 966-6) cyanide cultivars of cassava at progressive days after seed germination. In both varieties, linamarin biosynthesis peaked when the plants were about 45 days old, and then declined. However, during the period when linamarin biosynthesis was most rapid, the high-cyanide variety produced four times as much linamarin as the low-cyanide variety. After 83 days, both cultivars maintained similarly low levels of 14C-linamarin in their leaves. Levels of labelled linamarin in petioles, i.e. transported linamarin, showed similar trends as those seen in leaves. These data suggest that increased levels of cyanogenic glycosides in high-cyanide roots is due to both higher biosynthesis in leaves and transport to the roots in young cassava plants.
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