Abstract
Regulation of water flow in an interconnected xylem vessel network enables plants to survive despite challenging environment changes that can cause xylem embolism. In this study, vulnerability to embolisms of xylem vessels and their water-refilling patterns in vascular bundles of maize leaves were experimentally investigated by employing synchrotron X-ray micro-imaging technique. A vascular bundle in maize consisted of a protoxylem vessel with helical thickenings between two metaxylem vessels with single perforation plates and nonuniformly distributed pits. When embolism was artificially induced in excised maize leaves by exposing them to air, protoxylem vessels became less vulnerable to dehydration compared to metaxylem vessels. After supplying water into the embolized vascular bundles, when water-refilling process stopped at the perforation plates in metaxylem vessels, discontinuous radial water influx occurred surprisingly in the adjacent protoxylem vessels. Alternating water refilling pattern in protoxylem and metaxylem vessels exhibited probable correlation between the incidence location and time of water refilling and the structural properties of xylem vessels. These results imply that the maintenance of water transport and modulation of water refilling are affected by hydrodynamic roles of perforation plates and radial connectivity in a xylem vascular bundle network.
Highlights
Plants transport water and dissolved minerals through xylem vessels composed of dead lignified cells (Zimmermann and Brown, 1971; Holbrook et al, 2002)
The interdependence of refilling of discontinuous water columns from radial water influx in both metaxylem and protoxylem vessels was revealed in this study
Based on the water refilling patterns in the embolized vascular bundles, water moved from metaxylem to protoxylem vessels and vice versa (Figures 2–4)
Summary
Plants transport water and dissolved minerals through xylem vessels composed of dead lignified cells (Zimmermann and Brown, 1971; Holbrook et al, 2002). Plants are vulnerable to environmental changes because of their inherent passivity and immobility They have adapted to harsh environments and survived with their own indigenous strategies, such as stomatal gating (Hetherington and Woodward, 2003; Raven, 2014), ion-mediated flow regulation through pit membranes (Zwieniecki et al, 2001b; Nardini et al, 2011), and axial and radial transport of water in redundantly interconnected xylem vessels (Tyree et al, 1994; Loepfe et al, 2007; Fan et al, 2009). Xylem vessels are interconnected to provide redundancy in the network of hydraulic conduits, offering alternative pathways to bypass the embolized vessel element, and maintain stable water transport (Tyree et al, 1994; Loepfe et al, 2007)
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