Functional repair of embolized vessels in maize roots after temporal drought stress, as demonstrated by magnetic resonance imaging

Authors

  • Ilja Kaufmann,

    1. Lehrstuhl für Experimentelle Physik 5, Physikalisches Institut, Universität Würzburg, Am Hubland, D–97074 Würzburg, Germany;
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  • Thomas Schulze-Till,

    1. Lehrstuhl für Experimentelle Physik 5, Physikalisches Institut, Universität Würzburg, Am Hubland, D–97074 Würzburg, Germany;
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  • Heike U. Schneider,

    1. Lehrstuhl für Biotechnologie, Biozentrum, Universität Würzburg, Am Hubland, D–97074 Würzburg, Germany;
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  • Ulrich Zimmermann,

    1. Lehrstuhl für Biotechnologie, Biozentrum, Universität Würzburg, Am Hubland, D–97074 Würzburg, Germany;
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  • Peter Jakob,

    1. Lehrstuhl für Experimentelle Physik 5, Physikalisches Institut, Universität Würzburg, Am Hubland, D–97074 Würzburg, Germany;
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  • Lars H. Wegner

    1. Lehrstuhl für Biotechnologie, Biozentrum, Universität Würzburg, Am Hubland, D–97074 Würzburg, Germany;
    2. (current address) Plant Bioelectrics Group, Karlsruhe Institute of Technology, Campus North, Building 630, Hermann-v-Helmholtz Platz 1, D–76344 Eggenstein-Leopoldshafen, Germany
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Author for correspondence:
Lars H. Wegner
Tel:+49 7247 824302
Email: Lars.Wegner@ihm.fzk.de

Summary

  • • Xylem sap under high tension is in a metastable state and tends to cavitate, frequently leading to an interruption of the continuous water columns. Mechanisms of cavitation repair are controversially discussed.
  • • Magnetic resonance (MR) imaging provides a noninvasive, high spatial and temporal resolution approach to monitor xylem cavitation, refilling, and functionality.
  • • Spin density maps of drought-stressed maize taproots were recorded to localize cavitation events and to visualize the refilling processes; c. 2 h after release of the nutrient solution from the homemade MR imaging cuvette that received the root, late metaxylem vessels started to cavitate randomly as identified by a loss of signal intensity. After c. 6 h plants were rewatered, leading to a repair of water columns in five out of eight roots. Sap ascent during refilling, monitored with multislice MR imaging sequences, varied between 0.5 mm min−1 and 3.3 mm min−1. Flow imaging of apparently refilled vessels was performed to test for functional repair. Occasionally, a collapse of xylem vessels under tension was observed; this collapse was reversible upon rewatering.
  • • Refilling was an all-or-none process only observed under low-light conditions. Absence of flow in some of the apparently refilled vessels indicates that functionality was not restored in these particular vessels, despite a recovery of the spin density signal.

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