Passive CO2 fluxes in four diatoms

Range Table - link
Organism Diatoms
Reference Hopkinson BM, Dupont CL, Allen AE, Morel FM. Efficiency of the CO2-concentrating mechanism of diatoms. Proc Natl Acad Sci U S A. 2011 Mar 8 108(10):3830-7. doi: 10.1073/pnas.1018062108 p.3 table 1PubMed ID21321195
Method P.1 right column 3rd paragraph: "The bulk of [investigators’] experiments consist of time courses of 18O depletion from labeled inorganic carbon, a process catalyzed by the presence of the enzyme carbonic anhydrase (CA) in cells. CA, which catalyzes the hydration of CO2 and dehydration of HCO3−, plays critical roles in CCMs [CO(2) concentrating mechanisms] and is present in all [their] experimental organisms: Thalassiosira weissflogii, T. pseudonana, T. oceanica, and Phaedactylum tricornutum, (SI Text, Experimental Organisms)."
Comments P.6 left column bottom paragraph: "[Investigators’] data show unequivocally that the cytoplasmic membranes of diatoms present a minimal barrier to CO2 diffusion (Table 1 and Fig. 1B). Generalizing from [their] 18O exchange data from a P. tricornutum strain overexpressing a chloroplast-localized CA [Carbonic Anhydrase], [they] infer that this is also true of the chloroplast membrane. Such high permeability to CO2 has been observed in other lipid bilayers, such as red blood cell membranes (ref 14), although studies of green algae indicate that their membranes inhibit CO2 passage to some extent, with CO2 permeabilities as low as 8 × 10^−4 cm/s being reported (refs 10, 11). Such high permeability to small uncharged molecules presents a problem for accumulating CO2, but it is presumably also helpful in avoiding the accumulation of O2, which would lead to high concentrations of noxious reactive oxygen species in photosynthesizing cells."
Entered by Uri M
ID 116873