Abstract
Long-distance water transport through plant xylem is vulnerable to hydraulic dysfunction during periods of increased tension on the xylem sap, often coinciding with drought. While the effects of local and systemic embolism on plant water transport and physiology are well documented, the spatial patterns of embolism formation and spread are not well understood. Using a recently developed nondestructive diagnostic imaging tool, high-resolution x-ray computed tomography, we documented the dynamics of drought-induced embolism in grapevine (Vitis vinifera) plants in vivo, producing the first three-dimensional, high-resolution, time-lapse observations of embolism spread. Embolisms formed first in the vessels surrounding the pith at stem water potentials of approximately -1.2 megapascals in drought experiments. As stem water potential decreased, embolisms spread radially toward the epidermis within sectored vessel groupings via intervessel connections and conductive xylem relays, and infrequently (16 of 629 total connections) through lateral connections into adjacent vessel sectors. Theoretical loss of conductivity calculated from the high-resolution x-ray computed tomography images showed good agreement with previously published nuclear magnetic resonance imaging and hydraulic conductivity experiments also using grapevine. Overall, these data support a growing body of evidence that xylem organization is critically important to the isolation of drought-induced embolism spread and confirm that air seeding through the pit membranes is the principle mechanism of embolism spread.
Highlights
Long-distance water transport through plant xylem is vulnerable to hydraulic dysfunction during periods of increased tension on the xylem sap, often coinciding with drought
Embolism spread between conduits is necessarily dependent on the number and orientation of the interconduit connections, but little is known about the organization of those connections or the spatial dynamics of embolism spread in vivo (Tyree and Zimmermann, 2002; Brodersen et al, 2010)
Despite the availability of NMR, studies using this technology are largely focused to the spread of embolism over long periods of time rather than the shortterm dynamics of embolism spread over the course of a few hours
Summary
Long-distance water transport through plant xylem is vulnerable to hydraulic dysfunction during periods of increased tension on the xylem sap, often coinciding with drought. Using a recently developed nondestructive diagnostic imaging tool, high-resolution x-ray computed tomography, we documented the dynamics of drought-induced embolism in grapevine (Vitis vinifera) plants in vivo, producing the first three-dimensional, highresolution, time-lapse observations of embolism spread. The spatial organization of xylem conduits plays a critical role in embolism repair and is likely even more influential in embolism spread, as direct connections between conduits are the most likely pathway through the network Building on these findings and new techniques, we aimed to take advantage of HRCT imaging to provide the first high-resolution visualization of the spread of drought-induced embolism
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