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Title:   Author  item
                                            KNIPFER, THORSTEN - University Of Californiaitem
                                            FEI, JIONG - University Of Californiaitem
                                            GAMBETTA, GREG - University Of Bordeauxitem
                                            McElrone, Andrewitem
                                            SHACKEL, KEN - University Of Californiaitem
                                            MATTHEWS, MARK - University Of California
  Submitted to: Plant Physiology
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 6/12/2015
                                    Publication  Date: 6/15/2015
                                    Citation: Knipfer, T., Fei, J., Gambetta, G., Mcelrone, A.J., Shackel, K., Matthews, M. 2015. Water transport properties of the grape (V. vinifera L.) pedicel during fruit development: Insights into xylem anatomy and function using microtomography. Plant Physiology. doi: 10.1104/pp.15.00031.Interpretive Summary:
                                Technical Abstract: Xylem flow into the fruit decline at the onset of ripening (i.e. veraison) in grapes, and current literature suggests that there is an increase in hydraulic resistance in the pedicel at this time.  However, it is unknown how pedicel hydraulic properties change developmentally in relation to xylem anatomy and function. From 20 to 90 days after anthesis, we determined pedicel hydraulic conductance (kh) for grapes (Vitis vinifera L. cv. Cabernet Sauvignon) using hydrostatic as well as osmotic driving forces, and investigated xylem structure and function using fluorescent light microscopy and x-ray computed microtomography (microCT). Osmotic kh was consistently four orders of magnitude lower than hydrostatic kh, but both declined before veraison (i.e. by ~40 %) and substantially over fruit development. The decline occurred for both low (< 0.08 MPa) and high (> 0.1 MPa) hydrostatic driving forces, and for both water in- and out-flow conditions at a low driving force. Pedicel xylem cross-sectional area increased by 2-3 fold over development, but specific hydraulic conductance (ks, i.e. kh per xylem area) decreased in a similar fashion to kh, indicating that an increase in xylem area did not compensate for the loss in water transport capacity over development. Based on microCT analysis, the loss in pedicel kh could be attributed to the formation of blockages in the vessel lumen (i.e. xylem occlusions). Air embolism formations in the pedicel were not detected before or after veraison.  MicroCT data indicated that vessels in the post-veraison pedicel are well inter-connected, and hence that vessel blockages can be circumvented, and that a functional xylem flow pathway remains and can accommodate recycling of excess water that may arrive in the fruit via the phloem.


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