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The tobacco aquaporin NtAQP1 is a membrane CO2 pore with physiological functions

Abstract

Aquaporins, found in virtually all living organisms, are membrane-intrinsic proteins that form water-permeable complexes. The mammalian aquaporin AQP1 has also shown CO2 permeability when expressed heterologously in Xenopus oocytes1, although whether this is a biochemical curiosity or of physiological significance is a matter of debate2,3. Here we report that, in the same expression system, a CO2 permeability comparable to that of the human AQP1 is observed for the tobacco plasma membrane aquaporin NtAQP1. NtAQP1 facilitates CO2 membrane transport in the homologous plant system at the cellular level, and has a significant function in photosynthesis and in stomatal opening. NtAQP1 overexpression heightens membrane permeability for CO2 and water, and increases leaf growth. The results indicate that NtAQP1-related CO2 permeability is of physiological importance under conditions where the CO2 gradient across a membrane is small, as is the case between the atmosphere and the inside of a plant cell.

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Figure 1: Representative kinetics of the pH decrease in a Xenopus oocyte injected with carbonic anhydrase only (dotted line) or with additional expression of NtAQP1.
Figure 2: Equal amounts of total RNA (10 µg) were loaded on a gel, blotted and hybridized to a gene-specific probe for NtAQP1 or to 28S-rRNA as loading control.
Figure 3: Incorporation of 14C into acid-precipitated compounds after incubation with 14CO2.
Figure 4: Kinetics of stomatal conductance from plants kept in the darkness and illuminated with 250 µmol m-2 s-1 PPFD at time 0.

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Acknowledgements

We thank W. M. Kaiser, M. Eckert and A. Schubert for discussion and help in experimental design.

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Correspondence to Ralf Kaldenhoff.

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Uehlein, N., Lovisolo, C., Siefritz, F. et al. The tobacco aquaporin NtAQP1 is a membrane CO2 pore with physiological functions. Nature 425, 734–737 (2003). https://doi.org/10.1038/nature02027

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