Distinguishing between extra‐ and intracellular iron in marine phytoplankton.

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Abstract
Iron associated with marine phytoplankton occurs adsorbed to and precipitated on cell surfaces in addition to being in metabolically active or stored intracellular forms. We demonstrate the utility of the inorganic reductant titanium(III) complexed by citrate and EDTA as a reagent for rapidly dissolving extracellular iron at pH 8 without causing cell breakage or toxicity. The method allows an experimental distinction to be made between extra‐ and intracellular iron, even in the presence of large quantities of precipitated iron hydroxides. Our results confirm previous work showing that such a distinction is essential for the study of transplasmalemma iron transport by these and other aquatic organisms.