EMERGING PATTERNS OF PHLOROTANNIN SYNTHESIS AND RESOURCEALLOCATION IN MARINE BROWN ALGAE

Thomas M. Arnold and Nancy M. Targett
University of Delaware, Graduate College of Marine Studies, Lewes DE 19958

Ecological models of plant-herbivore interactions presume that allelochemicalsare costly. Attempts to estimate the cost of chemical defense by correlatingstatic allelochemical concentrations with growth or reproduction have yieldedmixed results. As an alternative, we quantified in situ rates ofphlorotannin synthesis and turnover for various algal species by measuringthe assimilation of a stable isotope (13C) and subsequently analyzing isolatedproducts. Rates of de novo synthesis and turnover (mg product/gtissue/h) were compared to previously reported rates of phlorotannin accumulation. The interactive effects of biotic (grazing) and abiotic stresses (irradiance,nutrition) on resource allocation, allelochemical synthesis, observed ratesof polymerization (“aging”), and metabolite turnover were also evaluated. In general, seaweeds allocated ~1% of assimilated 13C to phlorotannin production,indicating that there may not be a significant metabolic cost in termsof carbon allocation.