Monoterpenoid plant-plant interactions upon herbivory

Monoterpene production by plants is not only dependent on the plant ability to produce secretory tissues where these molecules are accumulated. All plants are able to emit monoterpenes upon stress of both biotic and abiotic origin. Biotic stress induced by herbivory triggers the activation of signaling pathways eventually leading to the expression of genes coding for enzymes responsible for monoterpene emission. The emitted monoterpenes are used to defend the plant directly (in the case of terpenoid storing plants) and indirectly (for most of all other plants). Herbivore-induced monoter- pene emission is perceived as a signal by neighboring plants. This activates specific defense responses in primed plants. This minireview describes herbivore-induced monoterpene production and the effect of emitted monoterpenes on plants with particular reference to calcium signaling.