Abstract
CO(2) entry into Synechococcus sp. PCC7942 cells was drastically inhibited by the water channel blocker p-chloromercuriphenylsulfonic acid suggesting that CO(2) uptake is, for the most part, passive via aquaporins with subsequent energy-dependent conversion to HCO3(-). Dependence of CO(2) uptake on photosynthetic electron transport via photosystem I (PSI) was confirmed by experiments with electron transport inhibitors, electron donors and acceptors, and a mutant lacking PSI activity. CO(2) uptake was drastically inhibited by the uncouplers carbonyl cyanide m-chlorophenylhydrazone (CCCP) and ammonia but substantially less so by the inhibitors of ATP formation arsenate and N, N,-dicyclohexylcarbodiimide (DCCD). Thus a DeltamuH(+) generated by photosynthetic PSI electron transport apparently serves as the direct source of energy for CO(2) uptake. Under low light intensity, the rate of CO(2) uptake by a high-CO(2)-requiring mutant of Synechococcus sp. PCC7942, at a CO(2) concentration below its threshold for CO(2) fixation, was higher than that of the wild type. At saturating light intensity, net CO(2) uptake was similar in the wild type and in the mutant IL-3 suggesting common limitation by the rate of conversion of CO(2) to HCO3(-). These findings are consistent with a model postulating that electron transport-dependent formation of alkaline domains on the thylakoid membrane energizes intracellular conversion of CO(2) to HCO3(-).
Highlights
PCC7942 cells was drastically inhibited by the water channel blocker pchloromercuriphenylsulfonic acid suggesting that CO2 uptake is, for the most part, passive via aquaporins with subsequent energy-dependent conversion to HCO3؊
CO2 uptake has been observed to result in HCO3Ϫ accumulation in the cytoplasm where [CO2(dis)] is maintained below that expected at chemical equilibrium, and it has been inferred that a CA1-like activity is involved in its uptake and intracellular conversion to HCO3Ϫ (6, 14 –17)
We have recently suggested a working hypothesis according to which CO2 uptake by Cyanobacteria and its intracellular conversion to HCO3Ϫ may be energized by photosynthetic electron transport via the formation of alkaline domains on the stromal face of the thylakoid membrane [6]
Summary
Simultaneous measurements of argon and nitrogen concentrations were used to correct for variations or drifts in the system due to biological formation or consumption of O2 and CO2, small changes in the rate of stirring or temperature, and in the gas consumption by the mass spectrometer. The latter was minimized by using silicon tubing with a small surface area [7]. At plateaus in the curve, where the CO2 concentrations are relatively constant, the net rate of CO2 uptake by the cells will be equal to the net rate of CO2 formation by dehydration of HCO3Ϫ in the medium
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
