SULFATED FLAVONE GLYCOSIDE CHEMICALLY DEFENDS THE SEAGRASSTHALASSIA TESTUDINUM AGAINST ZOOSPORIC MARINE FUNGI
K.M. Jenkins, P.R. Jensen, D. Porter1 and W. Fenical
Scripps Institution of Oceanography, UCSD, La Jolla CA 92093
1The University of Georgia, Athens, GA 30602
As part of a survey of fungal associations with marine plants, it wasobserved that specimens of the seagrass Thalassia testudinum werecharacterized by a low yield of thraustochytrids (heterokont zoosporicmarine fungi) upon plating of the seagrass blades on an appropriate medium. However, autoclaved blades of Thalassia testudinum reintroducedto the field site for 48 hours yielded a significant number of thraustochytridsupon plating. In order to investigate the possible chemical mechanismsfor controlling fungal growth on the seagrass, chemical extracts of healthy,green blades of T. testudinum were tested for antibiotic activityin a disc diffusion assay against the thraustochytrid Schizochytriumaggregatum, isolated from decaying seagrass. Aqueous extractsof T. testudinum tested at natural concentration were found to inhibitthe growth of S. aggregatum. Furthermore, bioassay guidedfractionation of the seagrass extracts led to the isolation of an activesulfated flavone glycoside identified by NMR and mass spectrometry as luteolin-7-b-D-glucopyranosyl-2''-sulfate. To examine the effects of the compound in a more ecologically relevantbioassay, the pure compound was analyzed for antisettlement effects usingthraustochytrid zoospores and shown to inhibit settlement by 60% relativeto controls. These results suggest that seagrass metabolites providean effective chemical defense against zoosporic marine fungi.