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Published on March 25, 2009; 10.1104/pp.108.134098

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Received December 10, 2008
Accepted March 19, 2009

Roles of morphology, anatomy and aquaporins in determining contrasting hydraulic behavior of roots

Helen Bramley *, Neil C. Turner , David W. Turner , and Stephen D. Tyerman

Wine and Horticulture, School of Agriculture, Food and Wine, The University of Adelaide (Waite Campus), Plant Research Centre, PMB 1, Glen Osmond SA 5064, Australia; School of Plant Biology, Faculty of Natural and Agricultural Sciences, The University of Western Australia, 35 Stirling Highway, Crawley WA 6009, Australia; Centre for Legumes in Mediterranean Agriculture, M080, Faculty of Natural and Agricultural Sciences, The University of Western Australia, 35 Stirling Highway, Crawley WA 6009, Australia

* Corresponding author; email: helen.bramley{at}afhe.ualberta.ca.

The contrasting hydraulic properties of wheat (Triticum aestivum L.), narrow-leafed lupin (Lupinus angustifolius L.) and yellow lupin (L. luteus L.) roots were identified by integrating measurements of water flow, across different structural levels of organisation, with anatomy and modelling. Anatomy played a major role in root hydraulics, influencing axial conductance and the distribution of water uptake along the root, with a more localised role for aquaporins. Lupin roots had greater axial conductance (Lax) than wheat roots, due to greater xylem development. Axial and root hydraulic conductance (Lr) were related to each other, such that both variables increased with distance from the root tip in lupin roots. Lax and Lr were constant with distance from the tip in wheat roots. Despite these contrasting behaviors, the hydraulic conductivity of root cells (Lpc) was similar for all species and increased from the root surface towards the endodermis. Lpc was largely controlled by aquaporins, as demonstrated by dramatic reductions in Lpc by the aquaporin-blocker mercury. Modelling the root as a series of concentric, cylindrical membranes, and the inhibition of aquaporin 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 Lr. This study demonstrates the importance of examining root morphology and anatomy in assessing the role of AQPs in root hydraulics.






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