Abstract
ABSTRACT Previous reports suggest that in some plant species the refilling of embolized xylem vessels can occur while negative pressure exists in the xylem. The aim of this experiment was to use non‐destructive nuclear magnetic resonance imaging (MRI) to study the dynamics of xylem cavitation and embolism repair in‐vivo . Serial 1 H‐MRI was used to monitor the contents of xylem vessels in stems of two dicotyledonous ( Actinidia deliciosa and Actinidia chinensis , kiwifruit) and one monocotyledonous ( Ripogonum scandens , supplejack) species of woody liana. The configuration of the horizontal wide bore magnet and probe allowed the imaging of woody stems up to 20 mm in diameter. Tests using excised stems confirmed that the image resolution of 78 µ m and digital image subtraction could be used to detect the emptying and refilling of individual vessels. Imaging was conducted on both intact plants and excised shoots connected to a water supply. In the case of Ripogonum the excised shoots were long enough to allow the distal end of the shoot, including all leaves, to be exposed to ambient conditions outside the building while the proximal end was inside the MRI magnet. In total, six stems were monitored for 240 h while the shoots were subjected to treatments that included light and dark periods, water stress followed by re‐watering, and the covering of all leaves to prevent transpiration. The sudden emptying of water‐filled vessels occurred frequently while xylem water potential was low (below −0.5 MPa for Actinidia , −1.0 MPa for Ripogonum ), and less frequently after xylem water potential approached zero at the end of water‐stress treatments. No refilling of empty vessels was observed at any time in any of the species examined. It is concluded that embolism repair under negative pressure does not occur in the species examined here. Embolism repair may be more likely in species with narrower xylem vessels, but further experiments are required with other species before it can be concluded that repair during transpiration is a widespread phenomenon.
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Claims 6
Claim · model-written summary
MRI at 78 µ m resolution with subtraction detected emptying and refilling of individual xylem vessels.
Verbatim
e0“Tests using excised stems confirmed that the image resolution of 78 µ m and digital image subtraction could be used to detect the emptying and refilling of individual vessels.”
t0“woody lianas”
Claim · model-written summary
Water filled vessels emptied frequently below −0.5 MPa in Actinidia.
- Organ / stage
- vesselse0
- Outcome
- emptying of water‐filled vesselse0
- Value
- below −0.5 MPae0
- Qualifier
- xylem water potential was lowe0
ActinidiaOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The sudden emptying of water‐filled vessels occurred frequently while xylem water potential was low (below −0.5 MPa for Actinidia , −1.0 MPa for Ripogonum )”
Claim · model-written summary
Water filled vessels emptied frequently below −1.0 MPa in Ripogonum.
RipogonumOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The sudden emptying of water‐filled vessels occurred frequently while xylem water potential was low (below −0.5 MPa for Actinidia , −1.0 MPa for Ripogonum )”
Claim · model-written summary
Vessel emptying became less frequent as xylem water potential approached zero after water stress.
Verbatim
e0“and less frequently after xylem water potential approached zero at the end of water‐stress treatments.”
t0“woody lianas”
Claim · model-written summary
No empty vessels refilled in any examined species.
Verbatim
e0“No refilling of empty vessels was observed at any time in any of the species examined.”
t0“woody lianas”
Claim · model-written summary
The authors concluded embolism repair under negative pressure did not occur in the studied species.
Verbatim
e0“It is concluded that embolism repair under negative pressure does not occur in the species examined here.”
t0“woody lianas”