Abstract
In deciduous trees, measurement of stem water potential can be difficult during the leafless period in winter. By using thermocouple psychrometry, osmotic water potentials (Ψo; actual Ψo: Ψo(act); Ψo at full saturation: Ψo(sat)) of expressed sap of bark and bud tissue were measured in order to test if the severity of winter desiccation in apple stems could be sufficiently assessed with Ψo. Water potentials were related to frost resistance and freezing behaviour of buds. The determination of Ψo reliably allowed winter desiccation and osmotic adjustments in apple stem tissue to be assessed. In winter in bark tissue, a pronounced decrease in Ψo(act) and Ψo(sat) was found. Decreased Ψo(sat) indicates active osmotic adjustment in the bark as observed earlier in the leaves of evergreen woody plants. In terminal bud meristems, no significant osmotic adjustments occurred and dehydration during winter was much less. Osmotic water potentials, Ψo(act) and Ψo(sat), of bud tissue were always less negative than in the bark. To prevent water movement and dehydration of the bud tissue via this osmotic gradient, it must be compensated for either by a sufficiently high turgor pressure (Ψp) in bark tissue or by the isolation of the bud tissue from the bark during midwinter. During freezing of apple buds, freeze dehydration and extra-organ freezing could be demonstrated by significantly reduced Ψo(act) values of bud meristems that had been excised in the frozen state. Infrared video thermography was used to monitor freezing patterns in apple twigs. During extracellular freezing of intact and longitudinally dissected stems, infrared differential thermal analysis (IDTA) images showed that the bud meristem remains ice free. Even if cooled to temperatures below the frost-killing temperature, no freezing event could be detected in bud meristems during winter. In contrast, after bud break, terminal buds showed a second freezing at the frost-killing temperature that indicates deep supercooling. Our results demonstrate the applicability of thermocouple psychrometry for the assessment of winter desiccation in stem tissues of deciduous trees and corroborate the finding that dormant apple buds survive by extra-organ freezing and do not deep supercool. In addition, they indicate that significant changes of the frost-survival mechanism can occur during the apple bud development in spring.
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Claims 14
Claim · model-written summary
In winter, bark tissue of apple stems showed a pronounced decrease in osmotic water potentials Ψo(act) and Ψo(sat).
- Taxon
- apple
Malus domesticat0 - Organ / stage
- bark tissuee1
- Outcome
- Ψo(act) and Ψo(sat)e1
- Direction
- decreasee1
- Setting
- wintere1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“In winter in bark tissue, a pronounced decrease in Ψo(act) and Ψo(sat) was found”
t0“apple stem tissue”
Claim · model-written summary
Bud tissue osmotic water potentials were always less negative than those of bark in apple stems.
- Taxon
- appleMalus domesticat0
- Organ / stage
- bud tissuee1
- Outcome
- Ψo(act) and Ψo(sat)e1
- Direction
- less negativee1
- Comparator
- barke1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“Osmotic water potentials, Ψo(act) and Ψo(sat), of bud tissue were always less negative than in the bark”
t0“apple stem tissue”
Claim · model-written summary
In terminal bud meristems of apple, no significant osmotic adjustment occurred during winter.
- Taxon
- appleMalus domesticat0
- Organ / stage
- terminal bud meristemse1
- Outcome
- osmotic adjustmentse1
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“In terminal bud meristems, no significant osmotic adjustments occurred and dehydration during winter was much less”
t0“apple stem tissue”
Claim · model-written summary
Dehydration during winter was much less in terminal bud meristems of apple than in bark.
- Taxon
- appleMalus domesticat0
- Organ / stage
- terminal bud meristemse1
- Outcome
- dehydration during wintere1
- Direction
- lesse1
- Setting
- during wintere1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“In terminal bud meristems, no significant osmotic adjustments occurred and dehydration during winter was much less”
t0“apple stem tissue”
Claim · model-written summary
Osmotic potentials of excised frozen apple bud meristems were significantly reduced, indicating freeze dehydration.
- Taxon
- appleMalus domesticae1
- Organ / stage
- bud meristemse1
- Treatment
- excised in the frozen statee1
- Outcome
- Ψo(act) valuese1
- Direction
- reducede1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“During freezing of apple buds, freeze dehydration and extra-organ freezing could be demonstrated by significantly reduced Ψo(act) values of bud meristems that had been excised in the frozen state”
Claim · model-written summary
Freeze dehydration and extra-organ freezing were demonstrated in apple buds during freezing.
- Taxon
- appleMalus domesticae1
- Organ / stage
- budse1
- Treatment
- freezinge1
- Outcome
- freeze dehydration and extra-organ freezinge1
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“During freezing of apple buds, freeze dehydration and extra-organ freezing could be demonstrated”
Claim · model-written summary
During extracellular freezing of intact and longitudinally dissected apple stems, the bud meristem remained ice free.
- Taxon
- appleMalus domesticat0
- Organ / stage
- bud meristeme1
- Treatment
- extracellular freezinge1
- Outcome
- remains ice freee1
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“During extracellular freezing of intact and longitudinally dissected stems, infrared differential thermal analysis (IDTA) images showed that the bud meristem remains ice free”
t0“apple stem tissue”
Claim · model-written summary
No freezing event was detected in apple bud meristems during winter, even when cooled below the frost-killing temperature.
- Taxon
- appleMalus domesticat0
- Organ / stage
- bud meristemse1
- Treatment
- cooled to temperatures below the frost-killing temperaturee1
- Outcome
- freezing evente1
- Setting
- during wintere1
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“Even if cooled to temperatures below the frost-killing temperature, no freezing event could be detected in bud meristems during winter”
t0“apple stem tissue”
Claim · model-written summary
After bud break, terminal apple buds showed a second freezing at the frost-killing temperature.
- Taxon
- appleMalus domesticat0
- Organ / stage
- terminal budse1
- Treatment
- at the frost-killing temperaturee1
- Outcome
- second freezinge1
- Qualifier
- after bud breake1
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“In contrast, after bud break, terminal buds showed a second freezing at the frost-killing temperature that indicates deep supercooling”
t0“apple stem tissue”
Claim · model-written summary
The second freezing of terminal apple buds after bud break is taken to indicate deep supercooling.
- Taxon
- appleMalus domesticat0
- Outcome
- second freezinge1
- Qualifier
- deep supercoolinge1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“terminal buds showed a second freezing at the frost-killing temperature that indicates deep supercooling”
t0“apple stem tissue”
Claim · model-written summary
Dormant apple buds survive by extra-organ freezing and do not deep supercool.
- Taxon
- appleMalus domesticae1
- Organ / stage
- dormant apple budse1
- Outcome
- survivee1
- Qualifier
- by extra-organ freezinge1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“corroborate the finding that dormant apple buds survive by extra-organ freezing and do not deep supercool”
Claim · model-written summary
Significant changes of the frost-survival mechanism of apple buds can occur during bud development in spring.
- Taxon
- appleMalus domesticae1
- Organ / stage
- bud developmente1
- Outcome
- frost-survival mechanisme1
- Setting
- in springe1
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“significant changes of the frost-survival mechanism can occur during the apple bud development in spring”
Claim · model-written summary
The determination of osmotic potential by thermocouple psychrometry reliably allowed winter desiccation and osmotic adjustment in apple stem tissue to be assessed.
- Taxon
- appleMalus domesticae1
- Organ / stage
- stem tissuee1
- Outcome
- winter desiccation and osmotic adjustmentse1
- Qualifier
- reliablye1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Schema note from the model: method performance (thermocouple psychrometry) with no comparator or value stated; recorded as observation
Verbatim
e1“The determination of Ψo reliably allowed winter desiccation and osmotic adjustments in apple stem tissue to be assessed”
Claim · model-written summary
Decreased osmotic potential at saturation in apple bark indicates active osmotic adjustment.
- Taxon
- appleMalus domesticat0
- Organ / stage
- barke1
- Outcome
- Ψo(sat)e1
- Qualifier
- active osmotic adjustmente1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“Decreased Ψo(sat) indicates active osmotic adjustment in the bark”
t0“apple stem tissue”