Document: JAC-3-42-16

Variable biochemical responses by oaks to diverse environmental stimuli.

SCHULTZ, J.C.* ¹, S.D.ALLISON ² and T.SCHAEFFER ¹

Penn State University, University Park, PA 16802 USA ¹
Stanford University, Pal Alto, CA 94305 USA ²

Abstract:
Biochemical responses by oak trees to environmental stimuli like insects, wounding, light, and wind motion can be highly variable, and trees may even fail to respond to certain insects. To understand the basis of variation in responses by the trees, we have begun exploring the regulatory roles of within-plant signalling mechanisms. First year red oak seedlings were damaged by fourth-instar gypsy moth larvae over a two-week period in the greenhouse. Chemical analyses indicated that this stimulated condensed tannin accumulation compared with unattacked controls. Similar seedlings were then exposed to a wound hormone, jasmonic acid, every other day for two weeks. These trees exhibited increased condensed tannin concentrations very much like the gypsy moth-wounded trees, suggesting that the lipoxygenase/jasmonate wound signalling system widespread in other plants is also involved in oak responses to gypsy moths. We then examined enzymatic responses of the seedlings to gypsy moths, artificial wounding, jasmonates, and salicylate (a signal involved primarily in responses to pathogens). Seedlings were treated with gypsy moth larvae, paper punches, jasmonates and salicylate over a two-week period in the greenhouse. Various defense enzymes (peroxidase, polyphenoloxidase) and especially peroxidase isoforms were idiosyncratically induced by various stimuli and combinations of stimuli. Activities of individual peroxidase isoforms, which play a role in activating the polyphenol defenses of oaks, were tuned to specific signals, stimuli and their combinations. Red oak trees appear very flexible in their ability to perceive and respond differentially to environmental stimuli, including different insect attackers.

Keywords: induced defenses, wound signals, oak, peroxidase, tannins

This abstract is being presented at: 8:30 AM in session:
Oral Session #44: Terrestrial Invertebrates: Foodwebs and Plant Responses.