Nitrate regulation of Fe reduction and transport by Fe‐limited Thalassiosira oceanica
Nitrate regulation of Fe reduction and transport by Fe‐limited Thalassiosira oceanica
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铁限制海洋海链藻对铁还原和运输的硝酸盐调控
DOI：
10.4319/lo.2000.45.4.0814
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发表时间：
2000
影响因子：
4.5
通讯作者：
N. M. Price
中科院分区：
文献类型：
--
作者：
M. T. Maldonado;N. M. Price
在铁限制条件下，硝酸盐(NO3−)生长的海洋硅藻对细胞内铁的需求较高，但通过保持更快的稳态铁吸收速率，分裂速度与氨(NH4+)生长的细胞一样快或更快。在此，我们报道了Shalassiosira Ocean anica，克隆1003，具有铁还原酶，该酶能还原与多种有机配体结合的Fe(III)，包括铁载体去铁胺B(DFB)，这是一种高亲和力的Fe(III)特异性配体。还原是由细胞外介导的，由缺铁诱导。细胞Fe(III)还原速率在NO3-−-中明显快于在NH4+培养的培养中，提示与N代谢有关。在亚饱和铁浓度下，NO3−-细胞的短期和长期铁吸收速率也明显快于NH4+培养的细胞。结果表明，当铁限制时，浮游植物还原有机结合的铁(III)的速度较快，促进了铁的运输和生长。这些发现对于理解海洋水域浮游植物铁的营养具有重要意义，因为在海洋水域中，铁的形态以有机络合为主。我们推测，还原的铁运输途径可能使浮游植物能够直接利用与海洋中强有机配体结合的铁。
Under Fe‐limiting conditions, nitrate (NO3−)‐grown marine diatoms have higher intracellular Fe requirements, but divide as fast or faster than ammonium (NH4+)‐grown cells by maintaining faster steady‐state Fe uptake rates. Here we report that Thalassiosira oceanica, clone 1003, possesses an Fe reductase that reduces Fe(III) bound to a variety of organic ligands, including the siderophore desferrioxamine B (DFB), a high affinity, Fe(III)‐specific ligand. Reduction is mediated extracellularly and is induced by Fe deficiency. Cellular rates of Fe(III) reduction are significantly faster in NO3− ‐ than in NH4+ ‐grown cultures suggesting a link with N metabolism. At subsaturating Fe concentrations, short‐ and long‐term Fe uptake rates are also significantly faster in NO3− ‐ than in NH4+ ‐grown cells. The results suggest that when Fe is limiting, faster rates of reduction of organically bound Fe(III) by phyto‐plankton promote faster rates of Fe transport and growth. The implications of these findings could be significant for understanding phytoplankton Fe nutrition in oceanic waters where organic complexation dominates the speciation of Fe. We hypothesize that the reductive Fe transport pathway may enable phytoplankton to directly utilize Fe bound to strong organic ligands in the sea.