Fig. 3.

Ecological implications of immediate up-regulation of cyanogenic capacity (HCNc). In many cyanogenic plant species, HCNc (Lieberei, 1988) is regulated at genetic and transcriptional level. In these cases, an immediate modulation of HCNc (low HCNc to high HCNc and vice versa) as a result of herbivore or fungal attack is impossible. Therefore, the individual plant can only be herbivore- or pathogenic fungus-resistant (static defence reaction). In contrast, the activation of linamarase (LIN) and hydroxynitrile lyase (HNL) reported here results in immediate up-regulation of HCNc in response to severe, but not to minor, tissue damage (dynamic defence response). This may allow the combination of both properties (low and high HCNc) and might enable resistance to herbivores as well as to fungal pathogens. However, to date no data on cyanogenic plants resistant to both herbivores and HCN-resistant pathogenic fungi have been published. Pictures of leaf discs by: R. Lieberei and V. Noelting, University of Hamburg, Germany; D. J. Ballhorn, Portland State University, USA.