Test for Cyanogenic Compounds in Plants

Abstract

Many plants contain cyanogenic compounds. A disproportionate number of the most important cultivated human food plants are cyanogenic. Cyanogenic plants or plant parts resist microorganisms, insects, and vertebrate herbivores both in vivo and in storage and so it is possible that these plants were the successful ones during domestication because they were naturally protected against pests (Jones 1998). The production of hydrogen cyanide, HCN, termed cyanogenesis, depends on the degradation of a naturally occurring cyanogenic glycoside by an enzyme. A living plant normally keeps the substrate and the enzyme separate. They come together when the plant tissue is damaged, as by an herbivore chewing a leaf. Plants such as birdsfoot trefoil (Lotus corniculatus) and white clover (Trifolium repens) are polymorphic with regard to cyanogenesis. This means that different plant specimens of these species can range from being completely acyanogenic to showing various degrees of cyanogenesis. This variation can be correlated with presence of herbivores such as molluscs (Jones 1962; Ellis et al. 1977; D. Jones, pers. comm. 2009). Herbivores eat the acyanogenic specimens and therefore select for cyanogenic plants in a given population. Among the samples in the figure of this chapter, birdsfoot trefoil is cyanogenic, while white clover is not. Both samples came from a rural area near Syracuse, NY.