Wound-induced accumulations of condensed tannins in turtlegrass, Thalassia testudinum

Turtlegrass, Thalassia testudinum, produces high concentrations of proanthocyanidins (condensed tannins) which we hypothesized are induced by grazing, as a component of a general wound response. To test this we quantified condensed tannins in a variety of turtlegrass tissues following simulated fish grazing, grazing by the urchin Lytechinus variegatus, and treatment with the natural plant wound hormone jasmonic acid. We observed that simulated fish grazing triggered rapid induction of condensed tannins by an average of 10 mg tannin g−1 dry mass (DM) after 5 days. Condensed tannin accumulations were correlated with a reduction of blade extension rates. Further, we observed that constitutive tannin levels in developing first-rank leaves were strongly correlated with the width of second-rank leaves on each shoot, with an increase of 7.7 mg tannin g−1 tissue dry mass per millimeter blade width on average. We propose that wider source leaves provide additional resources for phenolic biosynthesis. There was no induction of tannins in leaves, meristematic or sheath tissues in response to grazing by the urchin L. variegatus, the presence of potential waterborne cues from nearby grazed plants, or to treatment with 5 mM jasmonic acid. However, urchin grazing did induce tannin production in root/rhizome tissues, where they accumulated to levels 3–4 times higher than in blades (up to ∼350 mg tannin g−1 tissue dry mass). These results confirm the potential for rapid wound-induced condensed tannin accumulations in T. testudinum. The link between blade widths and the tannin content of new leaves indicates that leaf morphology may be a useful bioindicator for predicting herbivore and disease-resistance in the field.