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Title: In vivo visualization of the final stages of xylem vessel refilling in grapevine (Vitis vinifera) stems

Author
item BRODERSEN, CRAIG - Yale University
item KNIPFER, THORSTEN - University Of California
item McElrone, Andrew

Submitted to: New Phytologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/22/2017
Publication Date: 1/1/2018
Citation: Brodersen, C., Knipfer, T., McElrone, A.J. 2018. In vivo visualization of the final stages of xylem vessel refilling in grapevine (Vitis vinifera) stems. New Phytologist. 217(1):117-126. https://doi.org/10.1111/nph.14811.
DOI: https://doi.org/10.1111/nph.14811

Interpretive Summary: Water scarcity threatens plant growth in natural and agricultural ecosystems worldwide. We studied the mechanism of how grapevines remove the final bits of air that remain in non-functional vessels that became gas filled upon drought stress. Using very high resolution x-ray micro computed tomography, we found that pit chambers in the xylem tube end walls are the last portion to contain air. This provides insight into details of grapevines unique ability to recover from previous drought stress.

Technical Abstract: Current theory predicts that successful xylem refilling resulting from drought or freeze-thaw events is necessarily dependent on the complete removal of trapped gas in the xylem network. Sustained negative pressures in the xylem sap upon reconnection to the transpiration stream would cause any residual gas to rapidly expand, thereby blocking water transport. Due to methodological limitations, uncertainty around the fate of the last remaining gas volumes in refilling conduits has persisted. Here, using time-lapse X-ray micro-computed tomography (microCT) imaging we present in vivo visualizations of xylem refilling in grapevine (Vitis vinifera) targeted at vessel endings and the intervessel and half-bordered vessel-parenchyma pits in close proximity. Prior to refilling, intervessel and end wall perforation plate pit chambers were almost universally evacuated, while the vessel-parenchyma pit chambers appeared to be water-filled, with the gas-water meniscus positioned at the pit channel opening. Refilling of the intervessel pits always preceded end wall refilling, and end wall pit chambers typically refilled sequentially across the perforation plate. Pit chamber geometry and the position of the gas-water meniscus within the refilling vessels allowed for the estimation of tissue-specific water potential estimates in the scanned stems. Our study provides direct visual evidence that supports some while refuting other aspects of current models of embolism removal and provides a new technique for observing the spatial and temporal dynamics of this enigmatic biophysical mechanism.