A chloroplast pump model for the CO2 concentrating mechanism in the diatom Phaeodactylum tricornutum

作者：Hopkinson Brian M^*

来源：Photosynthesis Research, 2014, 121(2-3): 223-233.

DOI：10.1007/s11120-013-9954-7

• CO2 concentrating mechanism
• Diatom
• Model

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 %26quot;chloroplast pump%26quot; 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.

• 出版日期2014-9