title: Grapevine petioles are more sensitive to drought induced embolism than stems: evidence from in vivo MRI and microcomputed tomography observations of hydraulic vulnerability segmentation.
abstract: The 'hydraulic vulnerability segmentation' hypothesis predicts that expendable distal organs are more susceptible to water stress-induced embolism than the main stem of the plant. In the current work, we present the first in vivo visualization of this phenomenon. In two separate experiments, using magnetic resonance imaging or synchrotron-based microcomputed tomography, grapevines (Vitis vinifera) were dehydrated while simultaneously scanning the main stems and petioles for the occurrence of emboli at different xylem pressures (Ψx ). Magnetic resonance imaging revealed that 50% of the conductive xylem area of the petioles was embolized at a Ψx of -1.54 MPa, whereas the stems did not reach similar losses until -1.9 MPa. Microcomputed tomography confirmed these findings, showing that approximately half the vessels in the petioles were embolized at a Ψx of -1.6 MPa, whereas only few were embolized in the stems. Petioles were shown to be more resistant to water stress-induced embolism than previously measured with invasive hydraulic methods. The results provide the first direct evidence for the hydraulic vulnerability segmentation hypothesis and highlight its importance in grapevine responses to severe water stress. Additionally, these data suggest that air entry through the petiole into the stem is unlikely in grapevines during drought.
authors.affiliation: Dipartimento di Scienze Agrarie e Ambientali, University of Udine, 33100, Udine, Italy.|INRA, UMR 547 PIAF/Université Blaise Pascal, F-63039, Clermont-Ferrand, France.
authors.forename: Uri
authors.initials: U
authors.lastname: Hochberg
authors.affiliation: Department of Viticulture and Enology, University of California, Davis, CA, 95616, USA.
authors.forename: Caetano
authors.initials: C
authors.lastname: Albuquerque
authors.affiliation: The Jacob Blaustein Institute for Desert Research, Ben-Gurion University of the Negev, Be'er Sheva, 84990, Israel.
authors.forename: Shimon
authors.initials: S
authors.lastname: Rachmilevitch
authors.affiliation: INRA, UMR 547 PIAF/Université Blaise Pascal, F-63039, Clermont-Ferrand, France.
authors.forename: Herve
authors.initials: H
authors.lastname: Cochard
authors.affiliation: Institute of Plant Sciences, Agricultural Research Organization, The Volcani Centre, Bet Dagan, 50250, Israel.
authors.forename: Rakefet
authors.initials: R
authors.lastname: David-Schwartz
authors.affiliation: School of Forestry and Environmental Studies, Yale University, New Haven, CT, 06511, USA.
authors.forename: Craig R
authors.initials: CR
authors.lastname: Brodersen
authors.affiliation: Department of Viticulture and Enology, University of California, Davis, CA, 95616, USA.|Crops Pathology and Genetics Research Unit, USDA-ARS, Davis, CA, 95616, USA.
authors.forename: Andrew
authors.initials: A
authors.lastname: McElrone
authors.affiliation: Forschungszentrum Jülich, Institute for Bio- and Geosciences, IBG-2: Plant Sciences, 52425, Jülich, Germany.
authors.forename: Carel W
authors.initials: CW
authors.lastname: Windt
mesh_terms: D055864:Droughts; D018547:Plant Stems / Q000502:physiology*; D027843:Vitis / Q000502:physiology*; D014867:Water / Q000502:physiology*; D055114:X-Ray Microtomography; D052584:Xylem / Q000502:physiology*
chemical_list: D014867:Water
keywords: Vitis vinifera; cavitation; hydraulic conductance; vulnerability curves; xylem