Positive pressure in xylem and its role in hydraulic function

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Schenk , H J , Jansen , S & Hölttä , T 2021 , ' Positive pressure in xylem and its role in hydraulic function ' , New Phytologist , vol. 230 , no. 1 , pp. 27-45 . https://doi.org/10.1111/nph.17085

Title: Positive pressure in xylem and its role in hydraulic function
Author: Schenk, H. Jochen; Jansen, Steven; Hölttä, Teemu
Other contributor: University of Helsinki, Viikki Plant Science Centre (ViPS)




Date: 2021-04
Language: eng
Number of pages: 19
Belongs to series: New Phytologist
ISSN: 0028-646X
DOI: https://doi.org/10.1111/nph.17085
URI: http://hdl.handle.net/10138/336474
Abstract: Although transpiration-driven transport of xylem sap is well known to operate under absolute negative pressure, many terrestrial, vascular plants show positive xylem pressure above atmospheric pressure on a seasonal or daily basis, or during early developmental stages. The actual location and mechanisms behind positive xylem pressure remain largely unknown, both in plants that show seasonal xylem pressure before leaf flushing, and those that show a diurnal periodicity of bleeding and guttation. Available evidence shows that positive xylem pressure can be driven based on purely physical forces, osmotic exudation into xylem conduits, or hydraulic pressure in parenchyma cells associated with conduits. The latter two mechanisms may not be mutually exclusive and can be understood based on a similar modelling scenario. Given the renewed interest in positive xylem pressure, this review aims to provide a constructive way forward by discussing similarities and differences of mechanistic models, evaluating available evidence for hydraulic functions, such as rehydration of tissues, refilling of water stores, and embolism repair under positive pressure, and providing recommendations for future research, including methods that avoid or minimise cutting artefacts.
Subject: bleeding
diurnal pressure
embolism refilling
guttation
rehydration
root pressure
seasonal pressure
stem pressure
MEMBRANE H+-ATPASE
STEM WATER-CONTENT
VESSEL-ASSOCIATED CELLS
FREEZE-THAW CYCLES
ROOT-PRESSURE
WINTER EMBOLISM
CONDUCTIVITY RECOVERY
SAP FLOW
REFLECTION COEFFICIENT
AQUAPORIN EXPRESSION
11831 Plant biology
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