Examining phenolic induction in Fraxinus americana in response to herbivory.

Abstract

Many plants contain chemical defenses known as secondary compounds; one of the most prevalent classes is known as phenolics. Certain plants have been known to induce phenolics in response to damage, while others maintain constant levels of phenolics even after damage. In order to determine if phenolic induction occurs in white ash trees (Fraxinus americana) in response to herbivory, leaflets were sampled to test for local induction (at the site of herbivory) and systemic induction (induction throughout the plant). Induction as a response to mechanical damage (e.g. slicing) was measured in order to remove a potential noisy variable from the results. Leaflets for the local/systemic test were eaten by forest tent caterpillars (Malacosoma disstria) and samples of induced leaflets were collected 24 hours after herbivory. The Folin-Denis analysis was used to determine the magnitude of change in phenolics between the constitutive and induced levels. Local induction was not found, but systemic induction was found to occur evenly between leaflets, despite predictions that there would be a spatial differences. One potential explanation for this was volatile gaseous compounds sending airborne cues to the undamaged leaflets, causing induction. Slicing was not found to cause significant levels of induction.