Mechanisms of Optimal Defense Patterns in Nicotiana attenuata: Flowering Attenuates Herbivory-elicited Ethylene and Jasmonate SignalingF

Abstract

To defend themselves against herbivore attack, plants produce secondary metabolites, which are variously inducible and constitutively deployed, presumably to optimize their fitness benefits in light of their fitness costs. Three phytohormones, jasmonates (JA) and their active forms, the JA‐isoleucine (JA‐Ile) and ethylene (ET), are known to play central roles in the elicitation of induced defenses, but little is known about how this mediation changes over ontogeny. The Optimal Defense Theory (ODT) predicts changes in the costs and benefits of the different types of defenses and has been usefully extrapolated to their modes of deployment. Here we studied whether the herbivore‐induced accumulation of JA, JA‐Ile and ET changed over ontogeny in Nicotiana attenuata, a native tobacco in which inducible defenses are particularly well studied. Herbivore‐elicited ET production changed dramatically during six developmental stages, from rosette through flowering, decreasing with the elongation of the first corollas during flower development. This decrease was largely recovered within a day after flower removal by decapitation. A similar pattern was found for the herbivore‐induced accumulation of JA and JA‐Ile. These results are consistent with ODT predictions and suggest that the last steps in floral development control the inducibility of at least three plant hormones, optimizing defense‐growth tradeoffs.

Floral volatiles interfere with plant attraction of parasitoids: ontogeny-dependent infochemical dynamics in Brassica rapa

“…For example, the production of a phytohormone associated with direct defense in the leaves of Nicotiana attenuata have been shown to decrease as plants enter the reproductive stage [50]. In our study, plants were constrained by the amount of resources present in the soil of their pots, and reached relatively small sizes at maturity (Figure 1).…”

Ethylene: traffic controller on hormonal crossroads to defense

“…In addition to its role in defense, ET is also known to be an important regulator of developmental processes, and accordingly, ET-dependent defense patterns change during development. For instance, treating Nicotiana attenuata leaves of various ages with saliva from the Manduca sexta caterpillar showed that induced ET emission decreased with leaf and plant age (Diezel et al, 2011).…”

Auxin Is Rapidly Induced by Herbivore Attack and Regulates a Subset of Systemic, Jasmonate-Dependent Defenses

“…Herbivore-induced jasmonate and ethylene signaling are influenced by plant development (Diezel et al, 2011a). To test whether plant development specifically influences M. sexta-induced IAA levels, we induced plants by simulated M. sexta attack and measured IAA levels in the leaves of early rosette, elongated, and flowering plants.…”