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Title:   Author  item
                                            HOCHBERG, URI - University Of Udineitem
                                            ALBUQUEERQUE, CAETANO - University Of Californiaitem
                                            RACHMILEVITCH, SHIMON - University Of Californiaitem
                                            HERVE, COCHARD - Ben Gurion University Of Negevitem
                                            DAVID-SCHWARTZ, RAKEFET - Agricultural Research Organization, Volcani Centeritem
                                            BRODERSEN, CRAIG - Yale Universityitem
                                            McElrone, Andrewitem
                                            WINDT, CAREL - Wageningen University
  Submitted to: Plant Cell and Environment
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 12/9/2015
                                    Publication  Date: 2/12/2016
                                    Citation: Hochberg, U., Albuqueerque, C., Rachmilevitch, S., Herve, C., David-Schwartz, R., Brodersen, C.R., Mcelrone, A.J., Windt, C.W. 2016. Grapevines petioles are more sensitive to drought induced embolism than stems: evidence from in vivo MRI and microCT observations of hydraulic vulnerability segmentation. Plant Cell and Environment. doi: 10.1111/pce.12688.Interpretive Summary: The water conducting tubes (xylem) of grapevine petioles (stems of leaves) were shown to be more susceptible to drought induced embolism compared to stems. This phenomenon was documented using a nuclear magnetic resonance imaging (MRI) and microCT (a type of CAT scan). This response has implications for irrigation management and understanding of plant responses to drought stress as maintenance of water delivery to leaves is crucial for photosynthetic carbon capture.
                                Technical Abstract: The concept ‘‘hydraulic vulnerability segmentation’’ represents a mechanism in which expendable distal organs (e.g. leaves attached to a woody shoot) are more susceptible to water-stress induced cavitation than the main stem of the plant. In the present work we present the first in-vivo observation of this phenomena. 
Intact shoots and petioles of grapevines (Vitis vinifera) were dehydrated while simultaneously imaged at different xylem tensions ('x). In the first experiment, samples were imaged using nuclear Magnetic Resonance Imaging (MRI) at high temporal resolution (every 25 min). The MRI results were confirmed by a second experiment that used synchrotron-based micro computed tomography (microCT) with high spatial resolution (3.2 μm).
MRI revealed that 50% of the conductive xylem area of the petioles was embolized at 'x= -1.54 MPa, while the shoots did not reach similar losses until a 'x of -1.9MPa. MicroCT confirmed these results showing approximately half the vessels in the petioles embolized at 'x of -1.6MPa, while very few were embolized in the shoots. Despite their higher vulnerability compared to shoots, petioles were shown to be more resistant to water-stress induced cavitation than previously measured with invasive hydraulic methods. 
The results present the first direct evidence for hydraulic vulnerability segmentation and highlight its importance in grapevine responses to severe water stress. The mechanism may help to explain the common phenomenon of leaf shedding in grapevines under drought.


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