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WHOLE PLANT AND ECOPHYSIOLOGY

Nitrate Control of Root Hydraulic Properties in Plants: Translating Local Information to Whole Plant Response^1,[OA]

Arnold Arboretum (A.G., Q.Y., M.A.Z.) and Organismic and Evolutionary Biology (N.M.H.), Harvard University, Cambridge, Massachusetts 02138

The sessile lifestyle of plants constrains their ability to acquire mobile nutrients such as nitrate. Whereas proliferation of roots might help in the longer term, nitrate-rich patches can shift rapidly with mass flow of water in the soil. A mechanism that allows roots to follow and capture this source of mobile nitrogen would be highly desirable. Here, we report that variation in nitrate concentration around roots induces an immediate alteration of root hydraulic properties such that water is preferentially absorbed from the nitrate-rich patch. Further, we show that this coupling between nitrate availability and water acquisition results from changes in cell membrane hydraulic properties and is directly related to intracellular nitrate concentrations. Split-root experiments in which nitrate was applied to a portion of the root system showed that the response is both localized and reversible, resulting in rapid changes in water uptake to the portions of the roots exposed to the nitrate-rich patch. At the same time, water uptake by roots not supplied with nitrate was reduced. We believe that the increase in root hydraulic conductance in one part causes a decline of water uptake in the other part due to a collapse in the water potential gradient driving uptake. The translation of local information, in this case nitrate concentration, into a hydraulic signal that can be transmitted rapidly throughout the plant and thus coordinate responses at the whole plant level, represents an unexpected, higher level physiological interaction that precedes the level of gene expression.

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: Maciej A. Zwieniecki (mzwienie{at}oeb.harvard.edu).

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www.plantphysiol.org/cgi/doi/10.1104/pp.108.122499

^* Corresponding author; e-mail mzwienie{at}oeb.harvard.edu.

Received May 2, 2008; accepted August 14, 2008; published August 27, 2008.

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