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Putative Role of Aquaporins in Variable Hydraulic Conductance of Leaves in Response to Light¹

Unité Mixte de Recherche 547, Physiologie Intégrée de l'Arbre Fruitier et Forestier, Institut National de la Recherche Agronomique, 63039 Clermont-Ferrand, France (H.C., T.S.B.); Unité Mixte de Recherche 547, Physiologie Intégrée de l'Arbre Fruitier et Forestier, Université Blaise Pascal, 63170 Aubière, France (J.-S.V., N.B., S.H., A.G., S.S.); Department of Renewable Resources, University of Alberta, Edmonton, Alberta, Canada T6G 2E3 (M.T.T.); and United States Forest Service, South Burlington, Vermont 05403 (M.T.T.)

Molecular and physiological studies in walnut (Juglans regia) are combined to establish the putative role of leaf plasma membrane aquaporins in the response of leaf hydraulic conductance (K_leaf) to irradiance. The effects of light and temperature on K_leaf are described. Under dark conditions, K_leaf was low, but increased by 400% upon exposure to light. In contrast to dark conditions, K_leaf values of light-exposed leaves responded to temperature and 0.1 mM cycloheximide treatments. Furthermore, K_leaf was not related to stomatal aperture. Data of real-time reverse transcription-polymerase chain reaction showed that K_leaf dynamics were tightly correlated with the transcript abundance of two walnut aquaporins (JrPIP2,1 and JrPIP2,2). Low K_leaf in the dark was associated with down-regulation, whereas high K_leaf in the light was associated with up-regulation of JrPIP2. Light responses of K_leaf and aquaporin transcripts were reversible and inhibited by cycloheximide, indicating the importance of de novo protein biosynthesis in this process. Our results indicate that walnut leaves can rapidly change their hydraulic conductance and suggest that these changes can be explained by regulation of plasma membrane aquaporins. Model simulation suggests that variable leaf hydraulic conductance in walnut might enhance leaf gas exchanges while buffering leaf water status in response to ambient light fluctuations.

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: Soulaiman Sakr (soulaiman.sakr{at}univ-bpclermont.fr).

www.plantphysiol.org/cgi/doi/10.1104/pp.106.090092

^* Corresponding author; e-mail soulaiman.sakr{at}univ-bpclermont.fr; fax 33–4–73–40–79–16.

Received September 20, 2006; accepted November 5, 2006; published November 17, 2006.

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