Copper(II) is reduced to Cu(I) extracellularly by marine and freshwater phytoplankton, but its biological significance is not firmly established. We studied the relationship between Cu(II) reduction and uptake in Thalassiosira oceanica, a diatom that was recently shown to possess functional copper uptake transporters (CTRs) that take up Cu(I). Inorganic and organic complexes of Cu(II) were reduced directly by reactions at the cell surface in proportion to Cu(II)‐ligand reduction potential. The rates of reduction were enhanced twofold in Cu‐limited cells, suggesting reduction was regulated by Cu nutritional state. Suppressing Cu(II) reduction caused a decrease in Cu uptake rate by 97% and addition of a Cu(I) complexing agent completely inhibited cell division and reduced Cu quota when Cu concentration was growth limiting. Thus, Cu(II) reduction was an obligatory first step in Cu uptake. Cu(II) reduction rate and growth rate of T. oceanica were proportional to Cu–ethylenediaminetetraacetic acid concentration and independent of inorganic Cu concentration in bulk solution. The results suggest that Cu(II) bound to organic ligands was reduced by extracellular cupric reductases and subsequently internalized. This reduction‐dependent uptake pathway may enable diatoms to use naturally occurring Cu(II) organic complexes in the sea.

中文翻译：

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海洋硅藻中依赖还原的铜吸收途径

海洋和淡水浮游植物在细胞外将铜（II）还原为铜（I），但其生物学意义尚未明确。我们研究了Thalassiosira oceanica中Cu（II）的减少与吸收之间的关系。，是最近被证明具有吸收铜（I）的功能性铜吸收转运蛋白（CTR）的硅藻。铜（II）的无机和有机配合物通过细胞表面反应直接还原，与铜（II）-配体的还原电位成正比。铜受限细胞的还原速率提高了两倍，这表明还原受铜营养状态的调节。抑制Cu（II）还原会导致Cu吸收率降低97％，并且当Cu浓度限制生长时，添加Cu（I）络合剂会完全抑制细胞分裂并减少Cu配额。因此，减少Cu（II）是吸收Cu的强制性第一步。铜（II）还原速率和生长速率T.大洋洲与铜乙二胺四乙酸浓度成正比，而与本体溶液中无机铜的浓度无关。结果表明，结合到有机配体的铜（II）被细胞外铜还原酶还原，然后被内在化。这种依赖还原的吸收途径可能使硅藻能够利用海洋中天然存在的Cu（II）有机复合物。