A chloroplast pump model for the CO2 concentrating mechanism in the diatom Phaeodactylum tricornutum
A chloroplast pump model for the CO2 concentrating mechanism in the diatom Phaeodactylum tricornutum
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DOI：
10.1007/s11120-013-9954-7
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发表时间：
2014-09-01
影响因子：
3.7
通讯作者：
Hopkinson, Brian M.
中科院分区：
文献类型：
--
作者：
Hopkinson, Brian M.
三角褐指藻无机碳（C-i）通量的分析表明，C-i从细胞质向叶绿体的转运是细胞内C-i通量的主要来源，也是CO2浓缩机制（CCM）的主要驱动力。这种通量驱动叶绿体基质中的C1积累，并在细胞质中产生CO2缺乏，诱导CO2流入细胞。在这里，在三角褐指藻CCM的“叶绿体泵”模型被正式化，并评估其与CO2和HCO 3（-）吸收速率，碳酸酐酶（CA）活性，细胞内C-i浓度，细胞内pH值和RubisCO特性的数据的一致性。叶绿体泵模型可以解释数据的主要特征。光合和C-I吸收速率作为外部C-I浓度的函数的分析表明，该模型具有最困难的获得足够低的细胞质CO2浓度，以支持在低外部C-I浓度下观察到的CO2吸收速率，并实现高光合速率。有多种方法可以在合理的范围内改变模型参数，以匹配测量的光合作用和CO2吸收率。为了增加CO2吸收速率，可以增加CA活性，可以增强假定的叶绿体泵的动力学特性以增加HCO 3（-）输出，或者可以提高细胞质pH。为了提高光合速率，可以降低蛋白核对CO2的渗透性或增加RubisCO含量。
Prior analysis of inorganic carbon (C-i) fluxes in the diatom Phaeodactylum tricornutum has indicated that transport of C-i into the chloroplast from the cytoplasm is the major C-i flux in the cell and the primary driving force for the CO2 concentrating mechanism (CCM). This flux drives the accumulation of C-i in the chloroplast stroma and generates a CO2 deficit in the cytoplasm, inducing CO2 influx into the cell. Here, the "chloroplast pump" model of the CCM in P. tricornutum is formalized and its consistency with data on CO2 and HCO3 (-) uptake rates, carbonic anhydrase (CA) activity, intracellular C-i concentration, intracellular pH, and RubisCO characteristics is assessed. The chloroplast pump model can account for the major features of the data. Analysis of photosynthetic and C-i uptake rates as a function of external C-i concentration shows that the model has the most difficulty obtaining sufficiently low cytoplasmic CO2 concentrations to support observed CO2 uptake rates at low external C-i concentrations and achieving high rates of photosynthesis. There are multiple ways in which model parameters can be varied, within a plausible range, to match measured rates of photosynthesis and CO2 uptake. To increase CO2 uptake rates, CA activity can be increased, kinetic characteristics of the putative chloroplast pump can be enhanced to increase HCO3 (-) export, or the cytoplasmic pH can be raised. To increase the photosynthetic rate, the permeability of the pyrenoid to CO2 can be reduced or RubisCO content can be increased.