Effect of Simulated Herbivory On Protein Precipitable Phenolic Content of Desmodium Paniculatum.

Plant optimal defense theory is based on the assumption that the amount of resources a plant allocates to defense is determined by defense costs and benefits.  Previous studies have shown that plants invest energy into re-growth of relatively cheap photosynthetic tissue to offset lost leaf biomass or invest in energy expensive defenses to deter herbivores.  Condensed tannins (CT) are polyphenolic compounds produced by plants that bind protein and are hypothesized to be a plant defense mechanism.  Our study objective was to determine how protein precipitating polyphenolic content of leaves is affected by varying levels of simulated herbivory.  Individual plants of Desmodium paniculatum (panicledleaf ticktrefoil; PLTT), a North American native warm-season perennial herbaceous legume, were grown in a greenhouse and placed into one of five treatments.  Treatments included defoliation of 0, 25, 50, 75, and 100 percent of existing herbage in two successive defoliation events separated by 36 days.  Plants remained in the same treatment group throughout the experiment.  Protein precipitable polyphenolics (PPP) were determined by reacting extracts with bovine serum albumin (BSA).  Protein precipitable polyphenolics were similar (P > 0.05) for leaves from the second defoliation for plants in the 0, 25, 50, and 75% defoliation treatments.  However, plants that had 100% of leaves removed on the second defoliation had lower (P < 0.05) PPP levels than all other treatments, including those that were not defoliated at all suggesting that that plants defoliated at 100% might have lacked the resources to produce well defended leaves and instead opted to produce cheap photosynthetic tissue.  Results also suggest that as plants unexposed to simulated herbivory (0% treatment of defoliation 2) age, PPP increases.