Biochemical basis of the toxicity of manipueira (liquid extract of cassavaroots) to nematodes and insects

The presence of defence-related proteins and the concentration of cyanogens in the cell-sap solution of cassava roots (termed manipueira) have been in vestigated, It is demonstrated that manipueira is devoid of lectins, serine proteinase inhibitors and chitinase activity, although very low levels of alpha-amylase inhibitory activity were detected. Within 6 h of storage, all of the major cyanogenic glycoside of cassava, linamarin, had disappeared, while the concentration of acetone cyanohydrin, the breakdown product of th e hydrolysis of linamarin, had dropped to 40% of the initial value at zero time and remained unchanged until 72 h of storage, This stabilization of th e acetone cyanohydrin during storage seems to be caused both by a drop in p H due to lactic fermentation, which prevents its spontaneous breakdown, and by the absence of alpha-hydroxynitrile lyase in cassava roots. It is concl uded that the well-known toxicity of manipueira may be causally related to the stabilization of the acetone cyanohydrin, Copyright (C) 2000 John Wiley & Sons, Ltd.