Articles
Examining the effect of sap sugar concentration on fiber embolism in sugar maple (Acer saccharum)
Article number
1419_14
Pages
105 – 112
Language
English
Abstract
Sugar maple (Acer saccharum) develops elevated pressures in response to repeated cycles of freezing and thawing.
This pressure is theorised to develop due to compression of gas present within fibers.
Due to surface tension, the pressurised gas within fibers should rapidly dissolve.
That the gas persists over time is believed to be due to an osmotic barrier present between fibers and vessels that prevents sucrose from diffusing into fibers.
This creates sufficient osmotic pressure to prevent gas dissolution and so maintain fiber embolisms.
In our work we examine this hypothesis using synchrotron based microCT to produce high-resolution three-dimensional images of stem segments.
Using this technique, we directly resolved the gas present in the fibers.
Subsequently we perfused stem segments with either water or 2% sucrose and re-imaged the segments to examine any changes in fiber embolisms.
We also looked at samples that were frozen for 2-3 months to promote fiber embolism development, and for comparison we looked at silver birch (Betula pendula), a species that is thought to develop elevated stem pressures through a different mechanism than Acer. From the fresh stem segments, we observed fiber embolisms were indeed present, and that when perfused with sucrose solution there was little to no change in fiber embolisms, whereas in almost all cases perfusing with water led to partial or complete refilling of fiber embolisms, supporting the hypothesis.
The frozen samples did not display complete xylem embolization, in contrast to expectations, and showed complete refilling upon perfusion with either solution, suggesting cell damage had occurred.
The birch samples also showed fiber embolisms.
These embolisms remained after perfusing with sucrose solution, and there was some evidence the fiber embolisms refilled upon perfusion with water, however more samples are required to confirm these observations.
This pressure is theorised to develop due to compression of gas present within fibers.
Due to surface tension, the pressurised gas within fibers should rapidly dissolve.
That the gas persists over time is believed to be due to an osmotic barrier present between fibers and vessels that prevents sucrose from diffusing into fibers.
This creates sufficient osmotic pressure to prevent gas dissolution and so maintain fiber embolisms.
In our work we examine this hypothesis using synchrotron based microCT to produce high-resolution three-dimensional images of stem segments.
Using this technique, we directly resolved the gas present in the fibers.
Subsequently we perfused stem segments with either water or 2% sucrose and re-imaged the segments to examine any changes in fiber embolisms.
We also looked at samples that were frozen for 2-3 months to promote fiber embolism development, and for comparison we looked at silver birch (Betula pendula), a species that is thought to develop elevated stem pressures through a different mechanism than Acer. From the fresh stem segments, we observed fiber embolisms were indeed present, and that when perfused with sucrose solution there was little to no change in fiber embolisms, whereas in almost all cases perfusing with water led to partial or complete refilling of fiber embolisms, supporting the hypothesis.
The frozen samples did not display complete xylem embolization, in contrast to expectations, and showed complete refilling upon perfusion with either solution, suggesting cell damage had occurred.
The birch samples also showed fiber embolisms.
These embolisms remained after perfusing with sucrose solution, and there was some evidence the fiber embolisms refilled upon perfusion with water, however more samples are required to confirm these observations.
Publication
Authors
J.A. Robinson, M. Rennie, D.J. Holland, A. van den Berg, M. Clearwater, M.J. Watson
Keywords
sugar maple, silver birch, Acer saccharum, Betula pendula, embolism, microCT, synchrotron, sap, osmotic barrier
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