Chemical communication between roots and shoots: towards an integration of aboveground and belowground induced responses in plants

Abstract

Abstract. 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 leaf 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 plantdefence 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..

Physiological integration of roots and shoots in plant defense strategies links above‐ and belowground herbivory

“…2003, 2005; Bezemer & van Dam 2005; Soler et al. 2005, 2007; van Dam & Bezemer 2006; Kaplan & Denno 2007; Erb et al. 2008), the opposite effect can occur in systems where aboveground allelochemicals are produced belowground.…”

“…Last, we suspect that herbivore feeding guild may be a contributing factor. The focal root herbivore in our study is a gall‐forming nematode whose feeding style and effects on root morphology and physiology are entirely different than those of chewing insects, which to date are vastly over‐represented in the literature on plant‐mediated interactions (Bezemer & van Dam 2005; van Dam & Bezemer 2006; Kaplan & Denno 2007; Erb et al. 2008).…”

“…2005; van Dam et al. 2005; van Dam & Bezemer 2006; Kaplan & Denno 2007; Soler et al. 2007; Erb et al.…”

Constitutive and Induced Defenses to Herbivory in Above- And Belowground Plant Tissues

“…Despite the above predictions regarding defense induction between leaves and roots, we know from recent studies that cross-system induction is indeed possible (see reviews by Bezemer 2006). For instance, beetle larvae feeding on roots of Gossypium herbaceum elicit a more than fourfold increase in the concentration of terpenoids in mature leaves (Bezemer et al , 2004.…”

“…Consequently, ODT can be used to predict the relative expression of defenses in different parts of the same plant. For example, young leaves are considered more valuable than old leaves and often possess far greater concentrations of secondary metabolites (Krischik and Denno 1983, Raupp and Denno 1983, van Dam et al 1996, de Boer 1999, Ohnmeiss and Baldwin 2000. Similarly, flowers and fruits are more difficult to replace than vegetative parts and frequently possess high levels of resistance to herbivores (Euler and Baldwin 1996, Zangerl and Rutledge 1996, Darrow and Bowers 1999, Kozukue et al 2004).…”