Functional repair of embolized vessels in maize roots after temporal drought stress, as demonstrated by magnetic resonance imaging.
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.
Kaufmann
Ilja
I
Lehrstuhl für Experimentelle Physik 5, Physikalisches Institut, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany.
Schulze-Till
Thomas
T
Lehrstuhl für Experimentelle Physik 5, Physikalisches Institut, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany.
Schneider
Heike U
HU
Lehrstuhl für Biotechnologie, Biozentrum, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany.
Zimmermann
Ulrich
U
Lehrstuhl für Biotechnologie, Biozentrum, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany.
Jakob
Peter
P
Lehrstuhl für Experimentelle Physik 5, Physikalisches Institut, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany.
Wegner
Lars H
LH
Lehrstuhl für Biotechnologie, Biozentrum, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany.|(current address) Plant Bioelectrics Group, Karlsruhe Institute of Technology, Campus North, Building 630, Hermann-v-Helmholtz Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany.
D055864:Droughts; D009682:Magnetic Resonance Spectroscopy; D008954:Models, Biological; D053147:Plant Exudates / Q000378:metabolism; D018517:Plant Roots / Q000166:cytology / Q000502:physiology*; D018526:Plant Transpiration; D036226:Seedlings / Q000502:physiology; D013113:Spin Labels; D013312:Stress, Physiological; D013997:Time Factors; D052584:Xylem / Q000502:physiology*; D003313:Zea mays / Q000502:physiology*
D053147:Plant Exudates; D013113:Spin Labels