Uptake of ⁶⁴Cu-oxine by marine phytoplankton

Short-term uptake experiments using five phytoplankton species (Synechococcus clone DC2, Amphidinium carterae, Chrysochromulina polylepis, Ditylum brightwelli, and Prorocentrum micans) demonstrated rapid uptake of the lipophilic complex ⁶⁴Cu-oxine, presumably by diffusion of the complex across the plasma membrane. This passive uptake mechanism was extremely rapid and significantly faster than facilitated uptake by the free metal ion. Measured values of the observed permeability, P(obs), ranged from 0.55 to 18.6 x 10^-4 cm s^-1, showing only small differences between the various algal species. Removal rate constants, k(bio), varied much more widely, 0.009-570 x 10^-9 L cell^-1 h^-1, between the algae, indicating the influence of surface area on the uptake kinetics. Maximum internal Cu levels were reached after approximately 2 h, showing that a major limiting factor in the uptake of Cu from Cu-oxine is the concentration of intracellular Cu binding sites.