Surplus photosynthetic antennae complexes underlie diagnostics of iron limitation in a cyanobacterium.
Surplus photosynthetic antennae complexes underlie diagnostics of iron limitation in a cyanobacterium.
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DOI：
10.1371/journal.pone.0018753
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发表时间：
2011-04-20
期刊：
影响因子：
3.7
通讯作者：
Behrenfeld MJ
中科院分区：
文献类型：
--
作者：
Schrader PS;Milligan AJ;Behrenfeld MJ
浮游植物的叶绿素荧光提供了评估海洋中铁限制的工具，但荧光响应背后的生理机制尚不清楚。我们检查了模型蓝藻集胞藻 PCC6803 和同一物种的 ΔisiA 敲除突变体在三种模拟开放海洋营养条件的培养条件下生长的荧光特性：(1) 硝酸盐和铁充足，(2) 限制铁和高硝酸盐，代表天然高硝酸盐、低叶绿素区域，以及 (3) 铁和氮共同限制。我们表明，低可变荧光是铁限制的一个关键诊断，是由于天线复合体的合成远远超过光合反应中心铁限制池所能容纳的范围而产生的。在铁和氮共限条件下，没有多余的触角复合物，可变荧光很高。这些结果有助于解释高营养、低叶绿素海洋区域浮游植物的既定荧光特性，同时也解释了低铁、低氮区域缺乏这些特性的原因。重要的是，我们的结果完成了浮游植物中铁胁迫的独特分子后果与从太空对自然种群中铁胁迫的全球检测之间的联系。
Chlorophyll fluorescence from phytoplankton provides a tool to assess iron limitation in the oceans, but the physiological mechanism underlying the fluorescence response is not understood. We examined fluorescence properties of the model cyanobacterium Synechocystis PCC6803 and a ΔisiA knock-out mutant of the same species grown under three culture conditions which simulate nutrient conditions found in the open ocean: (1) nitrate and iron replete, (2) limiting-iron and high-nitrate, representative of natural high-nitrate, low-chlorophyll regions, and (3) iron and nitrogen co-limiting. We show that low variable fluorescence, a key diagnostic of iron limitation, results from synthesis of antennae complexes far in excess of what can be accommodated by the iron-restricted pool of photosynthetic reaction centers. Under iron and nitrogen co-limiting conditions, there are no excess antennae complexes and variable fluorescence is high. These results help to explain the well-established fluorescence characteristics of phytoplankton in high-nutrient, low-chlorophyll ocean regions, while also accounting for the lack of these properties in low-iron, low-nitrogen regions. Importantly, our results complete the link between unique molecular consequences of iron stress in phytoplankton and global detection of iron stress in natural populations from space.
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