Document: TOM-3-42-13

Induced poplar leaves call upon imported carbon resources to support the production of chemical defenses: Do source-sink dynamics constrain foliar responses to herbivores?

ARNOLD, T.M.* and J.C.SCHULTZ

The Pennsylvania State University, University Park PA 16802 ¹

Abstract:
Herbivore grazing commonly induces the production of polyphenols in woody plants, requiring a significant allocation of carbon resources to secondary metabolism. However, the precise origin of these resources in plants is unknown. For example, carbon resources may be supplied to the shikimic acid / phenylpropenoid pathway via local photosynthesis, cellular stores, or by the importation of sugars and metabolic precursors via vascular connections to exporting source tissues elsewhere in the canopy. To evaluate the relative importance of newly fixed vs. translocated resources in the development of induced defenses in Populus seedlings we utilized ¹³C, supplied as ¹³CO₂ in a flow-through system, as a metabolic tracer. Rates of ¹³C fixation, import, and export were determined by mass spectrometry for source and sink leaves sharing direct vascular connections. Also, the allocation of newly fixed vs. imported ¹³C to condensed tannins and phenolic glycosides was measured. The application of jasmonic acid, but not mechanical damage, induced condensed tannin accumulation and resulted in an increase in sink leaf ¹³C import, relative to control plants. Leaf photosynthesis rates were unaffected. Thus, young leaves of Populus induced by tissue damage called upon carbon resources translocated from source leaves. The magnitude of such induced responses and their distribution may be constrained by the availability of translocated carbon resources within plant canopies.

Keywords: Populus, chemical defense, ¹³C, resource allocation, source-sink relationships

This abstract is being presented at: 2:45 PM in session:
Oral Session #48: Anti-Predator Responses: Fish to Sagebrush.