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WHOLE PLANT AND ECOPHYSIOLOGY

Roles of Morphology, Anatomy, and Aquaporins in Determining Contrasting Hydraulic Behavior of Roots^1,[OA]

School of Agriculture, Food, and Wine, University of Adelaide (Waite Campus), Plant Research Centre, Glen Osmond, South Australia 5064, Australia (H.B., S.D.T.); School of Plant Biology, Faculty of Natural and Agricultural Sciences, University of Western Australia, Crawley, Western Australia 6009, Australia (H.B., D.W.T.); and Centre for Legumes in Mediterranean Agriculture, Faculty of Natural and Agricultural Sciences, University of Western Australia, Crawley, Western Australia 6009, Australia (N.C.T.)

The contrasting hydraulic properties of wheat (Triticum aestivum), narrow-leafed lupin (Lupinus angustifolius), and yellow lupin (Lupinus luteus) roots were identified by integrating measurements of water flow across different structural levels of organization with anatomy and modeling. Anatomy played a major role in root hydraulics, influencing axial conductance (L_ax) and the distribution of water uptake along the root, with a more localized role for aquaporins (AQPs). Lupin roots had greater L_ax than wheat roots, due to greater xylem development. L_ax and root hydraulic conductance (L_r) were related to each other, such that both variables increased with distance from the root tip in lupin roots. L_ax and L_r were constant with distance from the tip in wheat roots. Despite these contrasting behaviors, the hydraulic conductivity of root cells (Lp_c) was similar for all species and increased from the root surface toward the endodermis. Lp_c was largely controlled by AQPs, as demonstrated by dramatic reductions in Lp_c by the AQP blocker mercury. Modeling the root as a series of concentric, cylindrical membranes, and the inhibition of AQP activity at the root level, indicated that water flow in lupin roots occurred primarily through the apoplast, without crossing membranes and without the involvement of AQPs. In contrast, water flow across wheat roots crossed mercury-sensitive AQPs in the endodermis, which significantly influenced L_r. This study demonstrates the importance of examining root morphology and anatomy in assessing the role of AQPs in root hydraulics.

² Present address: Department of Renewable Resources, 4-44 ESB, University of Alberta, Edmonton, Canada T6G 2E3.

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: Helen Bramley (helen.bramley{at}afhe.ualberta.ca).

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.108.134098

^* Corresponding author; e-mail helen.bramley{at}afhe.ualberta.ca.

Received December 10, 2008; accepted March 19, 2009; published March 25, 2009.