PARENT SESSION
Poster Session #4: Herbivory.
Monday, August 5. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC

Testing the optimal defense theory and the growth-differentiation balance hypotheseis in Arabidopsis thaliana.

Barto, Kathryn^*,1, Cipollini, Don², ¹ Wright State University, Dayton, OH² Wright State University, Dayton, OH

ABSTRACT- Plants have two primary pathways of inducible plant defenses, those involving the plant hormones salicylic acid (SA) and jasmonic acid (JA). The salicylic acid pathway (SAR) is triggered primarily in response to pathogen attack and the jasmonic acid pathway (IR) primarily by herbivore attack. Two prominent theories explaining regulation of these pathways are the Optimal Defense Theory (ODT) and the Growth-Differentiation Balance Hypothesis (GDBH). The ODT suggests that the most valuable plant parts will be the most heavily defended, and the GDBH suggests that only slow growing plant parts will have the resources available for defense. We examined growth, value, and defense responses in several leaf classes of Arabidopsis thaliana to address whether patterns of defense expression in this plant fit either the ODT or the GDBH. We divided leaves of A. thaliana into six leaf classes based on three developmental stages: vegetative, bolting, and flowering; with two leaf ages at each stage: young and old. We assessed the value of each leaf class by removing those leaves and measuring seed production. Although A. thaliana proved to be highly tolerant to defoliation, young leaves were more valuable than old and young leaves on bolting plants were the most valuable leaf class. Finally, expression of inducible defenses was assessed in each leaf class by quantifying the expression of several defense-related proteins, and the defense genes PR-1 and PDF1.2. Support for the ODT or the GDBH varied depending upon which defenses were considered.

KEY WORDS: Arabidopsis thaliana, optimal defense theory, growth-differentiation balance, induced defenses