BROWN ALGAL POLYPHENOLS: PRIMARY METABOLITES WITH MULTIPLE, TRANSITIONAL ROLES

Arnold, Thomas M. Department of Biology, College/University of Charleston, Charleston S.C. 29424 Brown algal polyphenolics serve multiple functions. As defensive metabolites, they may serve to deter grazers, inhibit microbes, or absorb harmful UV radiation. However, these compounds are not classic ‘secondary metabolites’; they also have primary functions as cell wall strengtheners, spermatozoid inhibitors, and putative elements of algal holdfasts. These civilian roles of algal polyphenolics, which have been largely ignored in studies of plant defense, have implications for estimates of polyphenol cost. For example, in studies where growth‐defense tradeoffs are used to indicate a cost for a multi‐functional metabolite, the true cost is likely to have been significantly overestimated. To illustrate this, I propose a mechanism by which apparent growth vs. defense trade‐offs can be predicted in the absence of a true cost of algal polyphenolics or in the absence of any defensive role for these compounds. This transitional‐role model is based on the progression, or “aging” of phenolics and differentiates between physode‐bound (reactive) polyphenols and the oxidized (unreactive) wall components. It predicts that variations in the levels of brown algal phenolics measured by colorimetry result from changes in the synthesis –secretion balance. Potential tests of this model, including pathway‐ and gene‐level assessments of polyphenolic metabolism in brown algae, will be presented.