Figure 7.

Cellular uptake rates for Zn, Co, and Cd (normalized per mol of cell carbon) for the oceanic diatom Thalassiosira oceanica plotted as a function of the log₁₀ of the molar concentration of dissolved inorganic zinc species (Zn′). Concentrations of Cd′ and Co′ were held constant at 2.7 and 1.5 pM, respectively, within the range of values for near-surface ocean water (Bruland, 1992; Saito et al., 2004). Uptake rates for Cd and Co increase by at least two orders of magnitude when Zn′ concentrations decrease below 10⁻¹⁰ M. The large increase in uptake rates reflect the induction of a high-affinity cellular transport system (or systems) for Cd and Co in response to declining intracellular Zn levels or transport of the two metals into the cell by an inducible high-affinity Zn transport system. Data are from Sunda and Huntsman (2000).