Methyl jasmonate‐induced nicotine production in Nicotiana attenuata: inducing defenses in the field without wounding

The functional significance of herbivore‐induced plant traits known to directly or indirectly influence herbivore performance remains largely untested under field conditions due to the difficulty of uncoupling the response to herbivory from the act of herbivory. The signals that activate many of the induced responses in plants are endogenously produced in response to wounding, unlike many of the predator‐induced responses found in aquatic invertebrates (which are activated by exogenous cues derived from predators). Jasmonates, endogenously‐produced damage signals, activate diverse wound‐induced responses in plants including induced nicotine production in Nicotiana sylvestris. The results presented here are from two experiments which illustrate the use of jasmonates to uncouple induced nicotine production in Nicotiana attenuata (Torrey ex. Watson) from wounding. The exogenous addition of methyl jasmonate (MJ) in small quantities (11 μg for a 1.4 g dry mass plant) to roots of hydroponically‐grown plants induces de novo nicotine synthesis and increases whole‐plant nicotine concentrations just as wounding does. The MJ‐induced changes were proportional to the quantity of MJ given. Moreover, the effects of MJ were additive to the effects of damage. Applications of MJ to shoots were less effective. Root treatments also worked with plants growing in a field plot. The application of MJ represents a promising tool for examining the functional significance of induced nicotine responses in plants growing in their native environments.