Metabolite Distribution Within the Thallus

Studies that address the site of production, the transport, and the deposition of secondary metabolites provide another level of resolution that needs to be considered when evaluating the function of secondary metabolites and their patterns of distribution. Unlike approaches that quantify an alga s total metabolite concentration, studies that localize metabolites contained within algal tissues provide evidence of more subtle changes in metabolite distribution in response to stimuli and may clarify metabolite function. 

In brown algae, phlorotannins are localized in specialized bodies called physodes (Ragan 1976). Shifting the experimental approach, from chemical assays of total phlorotannin concentration to microscopic methods that describe physode transport and establish the timeframes at which phlorotannins accumulate in response to abiotic or biotic stimuli, has provided new insight into the understanding of phlorotannin production and function. It is known that physodes are derived from the endoplasmic reticulum (ER) and Golgi of the cell (Schoenwaelder and Clayton 2000). It appears that physodes are transferred across the cytosol and incorporated into the cell wall, where the phlorotannins are assumed to have a structural role and thus be involved in primary metabolism (Schoenwaelder and Clayton 2000 Arnold and Targett 2003). 

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