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ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS

Water Transport by Aquaporins in the Extant Plant Physcomitrella patens^1,[W]

Université de Rouen, CNRS UMR 6037, Institut Fédératif de Recherches Multidisciplinaires sur les Peptides, Faculté des Sciences Bât. Ext. Biologie, 76821 Mont-Saint-Aignan cedex, France (D.L., G.D., M.-C.K.-M., L.M.-B., V.G., J.-P.L.); and Station de Génétique et Amélioration des plantes, Institut National de la Recherche Agronomique, 78026 Versailles, France (F.N., F.C.)

Although aquaporins (AQPs) have been shown to increase membrane water permeability in many cell types, the physiological role of this increase was not always obvious. In this report, we provide evidence that in the leafy stage of development (gametophore) of the moss Physcomitrella patens, AQPs help to replenish more rapidly the cell water that is lost by transpiration, at least if some water is in the direct vicinity of the moss plant. Three AQP genes were cloned in P. patens: PIP2;1, PIP2;2, and PIP2;3. The water permeability of the membrane was measured in protoplasts from leaves and protonema. A significant decrease was measured in protoplasts from leaves and protonema of PIP2;1 or PIP2;2 knockouts but not the PIP2;3 knockout. No phenotype was observed when knockout plants were grown in closed petri dishes with ample water supply. Gametophores isolated from the wild type and the pip2;3 mutant were not sensitive to moderate water stress, but pip2;1 or pip2;2 gametophores expressed a water stress phenotype. The knockout mutant leaves were more bent and twisted, apparently suffering from an important loss of cellular water. We propose a model to explain how the AQPs PIP2;1 and PIP2;2 delay leaf dessication in a drying atmosphere. We suggest that in ancestral land plants, some 400 million years ago, APQs were already used to facilitate the absorption of water.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Jean-Paul Lassalles (jp.lassalles{at}univ-rouen.fr).

^[W] The online version of this article contains Web-only data.

www.plantphysiol.org/cgi/doi/10.1104/pp.107.111351

^* Corresponding author; e-mail jp.lassalles{at}univ-rouen.fr.

Received October 19, 2007; accepted December 20, 2007; published January 9, 2008.

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