Plant Physiology Preview
Published on November 17, 2006; 10.1104/pp.106.090092
Received September 20, 2006
Accepted November 5, 2006
New Insights into the Understanding of Variable Hydraulic Conductances in Leaves. Evidence for a Possible Implication of Plasma Membrane Aquaporins
Hervé Cochard , Jean-Stéphane Venisse , Têtè Sévérien Barigah , Nicole Brunel , Stéphane Herbette , Agnès Guilliot , Melvin T. Tyree , and Soulaiman Sakr *
Unité Mixte de Recherche 547-Physiologie Intégrée de d'Arbre Fruitier et Forestier ; Institut National de la Recherche Agronomique, Site de Crouel 63039 Clermont-Ferrand, France
Unité Mixte de Recherche 547, Physiologie Intégrée de l'Arbre Fruitier et Forestier, Université Blaise Pascal, 24 Avenue des Landais, 63170 Aubière, France
Department of Renewable Resources 338B Earth Sciences Building, University of Alberta Edmonton, AB, Canada, T6G 2E3 and the US Forest Service, 705 Spear St. South Burlington, Vermont, USA 05403
* Corresponding author; email: Soulaiman.Sakr{at}univ-bpclermont.fr.
Molecular and physiological studies in walnut are combined to establish the putative role of leaf plasma membrane aquaporins in the response of leaf hydraulic conductance (Kleaf) to irradiance. The effects of light and temperature on Kleaf are described. Under dark conditions Kleaf was low but increased by 400% upon exposure to light. In contrast to dark conditions, Kleaf values of light-exposed leaves responded to temperature and 0.1 mM cycloheximide treatments. Furthermore, Kleaf was not related to stomatal aperture. Data of real-time RT-PCR showed that Kleaf dynamics was tightly correlated with the transcript abundance of two walnut aquaporins (JrPIP2,1 and JrPIP2,2). Low Kleaf in dark was associated with down-regulation, while high Kleaf in light was associated with up-regulation of JrPIP2. Light responses of Kleaf and aquaporins 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 a regulation of plasma membrane aquaporins. Model simulation suggests that variable leaf hydraulic conductances in walnut might enhance leaf gas exchanges while buffering leaf water status in response to ambient light fluctuations.
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