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Abstract Detail

Xylem apoplast-symplast interactions

Secchi, Francesca [1], Zwieniecki, Maciej [1].

Understanding xylem refilling: molecular and physiological perspectives.

At any given moment, even in non-water-stressed plants, there is a pool of embolized conduits that reduce plant capacity to transport water. Many plant species counter embolism formation with a refilling process that can occur despite the presence of moderate tension. The mechanism of embolism repair is still not fully understood despite significant progress that has been made in the analysis of the physical conditions associated with refilling, including in vivo imaging, and determination of the role xylem parenchyma cells have in supplying both the energy and water needed for refilling. Here, we discuss the complexity of refilling based on information gained from the analysis of xylem sap chemistry, transcriptome and sugar metabolism. The transcriptome response to embolism revealed an in-depth view of multiple expression pathways that are responsible for facilitation of water transport across membranes, transport of ions and sugars, and cellular carbohydrate metabolism. This includes up-regulation of the disaccharide metabolism gene group, which contains genes involved in starch degradation, and down-regulation of genes from the monosaccharide metabolism category. Such a pattern of carbohydrate metabolism would promote the release of sucrose from starch that can be used as a source of energy needed to run the refilling process. The homeostasis that promotes the efflux of sugars out of cells will also require the activity of metal ion transporters to balance the “refilling” electrochemical potential, activity is facilitated by the up-regulation of these genes. Overall, the build-up of osmoticum outside of the cell could trigger an efflux of water that would be farther facilitated by strong up regulation of aquaporins. Predictions made on the basis of transcriptome data are supported by analysis of the chemical properties of the xylem sap collected from functional vessels and from non-functional vessels (embolized, that might undergoing refilling) showing significant changes in xylem sap pH and sugar/ion composition. Our results revealed the presence of both sugars and ions in non-functional vessels at elevated levels in comparison with liquid collected from functional vessels, in which only traces of sugars were found. The increased sugar concentration was accompanied by decreased xylem sap pH. With the increase of water stress in plants, the osmotic potential of liquid collected from non-functional vessels increased while its volume decreased. These results show the complexity of the interaction between aquaporin, ions, and sugar transporters, and imply that a large degree of hydraulic/physiological compartmentalization must exist in the xylem during the refilling process.

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1 - UC Davis, Plant Science, One Shields Avenue, Davis, CA, 95616, USA

embolism repair
xylem sap

Presentation Type: Symposium or Colloquium Presentation
Session: C3
Location: Belle-Chasse/Riverside Hilton
Date: Monday, July 29th, 2013
Time: 10:30 AM
Number: C3010
Abstract ID:262
Candidate for Awards:None

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