A day in the life in the dynamic marine environment: how nutrients shape diel patterns of phytoplankton photosynthesis and carbon fixation gene expression in the Mississippi and Orinoco River plumes
A day in the life in the dynamic marine environment: how nutrients shape diel patterns of phytoplankton photosynthesis and carbon fixation gene expression in the Mississippi and Orinoco River plumes
复制标题
动态海洋环境中的一天：营养物质如何影响密西西比河和奥里诺科河羽流中浮游植物光合作用和碳固定基因表达的昼夜模式
作者：
David E. John;J. M. López;Alvaro Cabrera;Nelson A. Santiago;J. Corredor;D. Bronk;J. Paul
这项研究解决了假设，环境条件影响的时间之间的连接每日转录的核酮糖-1，5二磷酸羧化酶/加氧酶（Rubisco）基因和浮游植物的光合能力。从表面样品收集的密西西比河羽流（MRP）和奥里诺科河羽流（ORP），我们的Rubisco（rbcL）mRNA的大小分级测量从四个浮游植物群（异鞭毛藻，haptophytes，聚球藻，原绿球藻）和叶绿素归一化光合作用辐照参数（包括光饱和光合速率-PmaxB），加上营养吸收和无机碳。叶绿素，光合作用，养分吸收，总rbcL mRNA水平显着更大的MRP。Rubisco mRNA和PmaxB表现出特征性的昼夜节律。时间偏移数据的回归显示光合作用周期与rbcL mRNA，但有一个时间滞后。这种延迟在MRP中更大，并且在> 2 μ m的细胞中更大。在这两个位点，<2 μ m细胞的PmaxB表现出更早的增加和更紧密的时间耦合到rbcL mRNA，表明碳固定在微型浮游生物更严格的转录控制。这些数据支持我们的假设，即在MRP中，高生产力和明显的营养胁迫（可能包括pCO2）导致更早的转录和更长的延迟，以增加PmaxB在较大的浮游植物。在胁迫下，较大的真核细胞可能需要更长的时间来翻译足够的Rubisco酶，因为细胞资源有限或转移到营养获取。在相对贫营养的ORP中，浮游植物可以通过限制Rubisco翻译的时间来保存细胞资源。这些发现提供了一个有趣的一瞥方式海藻可以调节生理学的碳固定，以应对环境挑战。
This research addresses the hypothesis that environmental conditions affect temporal connectivity between daily transcription of ribulose-1,5 bisphosphate carboxylase/oxygenase (Rubisco) genes and photosynthetic capacity among phytoplankton. From surface samples collected in the Mississippi River plume (MRP) and Orinoco River plume (ORP), we made size-fractionated measurements of Rubisco (rbcL) mRNA from four phytoplankton groups (heterokonts, haptophytes, Synechococcus, and Prochlorococcus) and chlorophyll-normalized photosynthesis–irradiance parameters (including light-saturated photosynthetic rate—PmaxB), plus nutrient uptake and inorganic carbon. Chlorophyll, photosynthesis, nutrient uptake, and total rbcL mRNA levels were substantially greater in the MRP. Rubisco mRNA and PmaxB exhibited characteristic diel patterns. Regressions with temporally offset data revealed photosynthesis cycles correlated to rbcL mRNA, but with a time lag. This delay was greater in the MRP, and greater among cells >2 μm. At both sites, PmaxB of <2 μm cells exhibited an earlier increase and closer temporal coupling to rbcL mRNA, suggesting carbon fixation is under tighter transcriptional control in picoplankton. The data support our hypothesis such that in the MRP, high productivity and apparent nutrient stress (perhaps including pCO2) resulted in earlier transcription and longer delay to increasing PmaxB among larger phytoplankton. Under stress, larger eukaryotic cells may need longer time to translate adequate Rubisco enzyme because of cellular resource limitation or diversion to nutrient acquisition. In the relatively oligotrophic ORP, phytoplankton may conserve cellular resources by restricting the time for Rubisco translation. These findings provide an interesting glimpse into ways marine algae can modulate the physiology of carbon fixation in response to environmental challenges.