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A requirement for sucrose in xylem sap flow from dormant maple trees
R W Johnson1, M T Tyree, M A Dixon
1Department of Botany, University of Toronto, Toronto, Ontario, Canada M5S 1A1.
Plant Physiology
|June 1, 1987
Summary
Maple tree stems absorb sap during freezing and release it during thawing, especially when sucrose is present. This sap flow response differs from other tree species studied, with larger sugars enhancing exudation.
Area of Science:
- Plant Physiology
- Tree Biology
- Cryobiology
Background:
- Understanding tree sap flow dynamics is crucial for forest ecology and maple syrup production.
- Freezing and thawing cycles significantly impact water transport in woody plants.
- Previous models, like the O'Malley-Milburn model, provide a framework for sap flow but require empirical validation across species.
Purpose of the Study:
- To investigate the differential response of excised tree stem segments to freezing and thawing cycles.
- To determine the role of sugars, particularly sucrose, in mediating sap exudation and absorption in maple (Acer spp.) stems.
- To compare the freezing-thawing response of maple stems with other tree species like Thuja occidentalis, Fagus grandifolia, and Betula papyrifera.
Main Methods:
- Excised stem segments from various tree species were subjected to controlled freezing and thawing cycles.
- Sap exudation and absorption were monitored during these cycles.
- Varying concentrations of sucrose and other sugars were introduced into the vessel sap to assess their effect on maple stem response.
Main Results:
- Thuja occidentalis, Fagus grandifolia, and Betula papyrifera stems exuded sap during freezing and absorbed it during thawing.
- Maple stems absorbed sap during freezing and exuded it during thawing only when sucrose was present in the vessel solution.
- Higher sucrose concentrations led to increased sap exudation in maples, and larger sugars (disaccharides and larger) could substitute for sucrose, while hexoses could not.
Conclusions:
- Maple stems exhibit a unique sap flow response to freezing and thawing, contingent on the presence and concentration of sucrose.
- The ability of larger sugars to elicit exudation suggests specific molecular interactions or osmotic effects influencing water movement in maple xylem.
- These findings contribute to a refined understanding of the O'Malley-Milburn model and the physiological mechanisms governing sap transport in trees under cryo-conditions.
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Like many living organisms, plants have tissues that specialize in specific plant functions. For example, shoots are well adapted to rapid growth, while roots are structured to acquire resources efficiently. However, sugar production is primarily restricted to the photosynthetic cells that reside in the leaves of angiosperm plants. Sugar and other resources are transported from photosynthetic tissues to other specialized tissues by a process called translocation.
02:03Xylem and Transpiration-driven Transport of Resources
The xylem of vascular plants distributes water and dissolved minerals that are taken up by the roots to the rest of the plant. The cells that transport xylem sap are dead upon maturity, and the movement of xylem sap is a passive process.
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During photosynthesis, plants acquire the necessary carbon dioxide and release the produced oxygen back into the atmosphere. Openings in the epidermis of plant leaves is the site of this exchange of gasses. A single opening is called a stoma—derived from the Greek word for “mouth.” Stomata open and close in response to a variety of environmental cues.
02:12Short-distance Transport of Resources
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