Phenotypic plasticity of cyanogenesis in lima bean Phaseolus lunatus - Activity and activation of β-glucosidase

Cyanogenesis, the release of toxic HCN from damaged plant tissues, is generally considered as a constitutive plant defense. We found phenotypic plasticity of cyanogenesis in young leaves of lima bean Phaseolus lunatus based on increased activity of the β-glucosidase in response to herbivore attack. Two aspects of plant cyanogenesis have to be considered in ecological analyses: (1) the cyanogenic potential (HCNp), which indicates the total amount of cyanide-containing compounds present in a given tissue, and (2) the cyanogenic capacity (HCNc), representing the release of HCN per unit time. This release is catalyzed by specific β-glucosidases, whose activity is a crucial parameter determining overall toxicity. Enzymatic activity of β-glucosidase - and, in consequence, the rate of HCN release - was increased significantly after 72 hr of incubation with spider mites as compared to noninfested leaves. Feeding by L1 larvae of Mexican bean beetles also led to enhanced enzymatic activity, whereas mechanical damage of leaf tissue had no effect on β-glucosidase activity and the release of HCN. The results place plant cyanogenesis in the group of induced resistance traits, whose degree of activity depends on the feeding by a particular herbivore. © 2006 Springer Science + Business Media, Inc.