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WHOLE PLANT AND ECOPHYSIOLOGY

Intact Plant Magnetic Resonance Imaging to Study Dynamics in Long-Distance Sap Flow and Flow-Conducting Surface Area¹

Laboratory of Biophysics and Wageningen Nuclear Magnetic Resonance Centre, Department of Agrotechnology and Food Sciences, Wageningen University, 6703 HA Wageningen, The Netherlands

Due to the fragile pressure gradients present in the xylem and phloem, methods to study sap flow must be minimally invasive. Magnetic resonance imaging (MRI) meets this condition. A dedicated MRI method to study sap flow has been applied to quantify long-distance xylem flow and hydraulics in an intact cucumber (Cucumis sativus) plant. The accuracy of this MRI method to quantify sap flow and effective flow-conducting area is demonstrated by measuring the flow characteristics of the water in a virtual slice through the stem and comparing the results with water uptake data and microscopy. The in-plane image resolution of 120 x 120 µm was high enough to distinguish large individual xylem vessels. Cooling the roots of the plant severely inhibited water uptake by the roots and increased the hydraulic resistance of the plant stem. This increase is at least partially due to the formation of embolisms in the xylem vessels. Refilling the larger vessels seems to be a lengthy process. Refilling started in the night after root cooling and continued while neighboring vessels at a distance of not more than 0.4 mm transported an equal amount of water as before root cooling. Relative differences in volume flow in different vascular bundles suggest differences in xylem tension for different vascular bundles. The amount of data and detail that are presented for this single plant demonstrates new possibilities for using MRI in studying the dynamics of long-distance transport in plants.

² Present address: Department of Radiology (667), Radboud University Nijmegen Medical Centre, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands.

³ Present address: Institute of Imaging Science, MCN Vanderbilt University, Nashville, TN 37232.

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: T.W.J. Scheenen (henk.vanas{at}wur.nl).

www.plantphysiol.org/cgi/doi/10.1104/pp.106.089250

^* Corresponding author; e-mail henk.vanas{at}wur.nl; fax 31–317–482725.

Received September 1, 2006; accepted April 16, 2007; published April 20, 2007.

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