Chemical communication between roots and shoots - Towards an integration of aboveground and belowground induced responses in plants

Induced responses in plants occur in response to both aboveground (AG) and belowground (BG) herbivores and pathogens. So far, the majority of studies have focused on AG induced responses. Possible interactions between AG and BG induced responses have only recently received scientific attention. On the one hand, induction in one plant part may result in systemically induced responses in other parts. On the other hand, simultaneously occurring AG and BG induced responses may interfere, for example, when the activities of root feeders alter the effectiveness of induced responses against lcaf feeders. In both cases, AG-BG interactions between induced responses may affect the amount of damage to a plant and therefore constitute an important selection pressure in the evolution of optimal plant-defence strategies. Here we present a new concept for the integration of AG and BG induced responses in current optimal-defence theory. First, we will consider differences in physiology and morphology between roots and shoots, which relate to their different roles in resource acquisition and which are important in interactions with their environment. Then, we will evaluate how general principles emerging from current theories and mathematical models of optimal AG induced plant defences can be applied to BG induced responses, as well as to their interactions with AG responses. Finally, we argue that plants integrate the information that is communicated by roots and shoots to optimize plant fitness in a multitrophic context.