Abstract
Here, the aim was to estimate loads imposed on the apoplastic ascorbate (ASC) pool by enzymatic and nonenzymatic reactions in Betula pendula exposed to doubled CO2 and O3 concentrations in open-top chambers. Leaf apoplastic extracts were analysed for peroxidase and oxidase activities in vitro, using different substrates. Partial loads in vivo were deduced using measured kinetic constants and substituted-enzyme catalysis approaches. Ascorbate use in O3 scavenging was calculated using measured stomatal conductances and ASC concentrations. Under elevated O3, stomatal conductance and O3 uptake were higher. O3 fluxes to the plasmalemma were levelled off by higher apoplastic ASC concentrations. The effect of CO2 enrichment on ASC concentrations under elevated O3 was minor. Under ambient O3, the ascending hierarchy of ASC users was: peroxidases, O3 scavenging, oxidases, coniferyl alcohol re-reduction. Under elevated O3, ASC use in O3 scavenging was higher than by oxidases. The redox state of ASC was not depressed by O3; there was no leaf injury. The cell wall/plasmalemma/cytosol system in birch had sufficient capacity to maintain ASC redox status in the apoplast, without necessity to restrict O3 uptake by stomatal closure.
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Claims 8
Claim · model-written summary
Elevated O3 increased stomatal conductance and O3 uptake in birch.
- Taxon
- Betula pendula
Betula pendulat0 - Treatment
- elevated O3e0
- Outcome
- stomatal conductance and O3 uptakee0
- Direction
- highere0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Under elevated O3, stomatal conductance and O3 uptake were higher.”
t0“Components of apoplastic ascorbate use in Betula pendula leaves exposed to CO2 and O3 enrichment”
Claim · model-written summary
Higher apoplastic ascorbate concentrations levelled off ozone fluxes to the plasmalemma.
- Taxon
- Betula pendulaBetula pendulat0
- Compound
- apoplastic ASC concentrationse0
- Outcome
- O3 fluxes to the plasmalemmae0
- Direction
- levelled offe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“O3 fluxes to the plasmalemma were levelled off by higher apoplastic ASC concentrations.”
t0“Components of apoplastic ascorbate use in Betula pendula leaves exposed to CO2 and O3 enrichment”
Claim · model-written summary
CO2 enrichment had a minor effect on ascorbate concentrations under elevated ozone.
- Taxon
- Betula pendulaBetula pendulat0
- Treatment
- CO2 enrichmente0
- Outcome
- ASC concentrationse0
- Direction
- minore0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The effect of CO2 enrichment on ASC concentrations under elevated O3 was minor.”
t0“Components of apoplastic ascorbate use in Betula pendula leaves exposed to CO2 and O3 enrichment”
Claim · model-written summary
Under ambient ozone, ascorbate use ranked from peroxidases through ozone scavenging and oxidases to coniferyl alcohol re-reduction.
- Taxon
- Betula pendulaBetula pendulat0
- Outcome
- ascending hierarchy of ASC userse0
- Qualifier
- Under ambient O3e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Under ambient O3, the ascending hierarchy of ASC users was: peroxidases, O3 scavenging, oxidases, coniferyl alcohol re-reduction.”
t0“Components of apoplastic ascorbate use in Betula pendula leaves exposed to CO2 and O3 enrichment”
Claim · model-written summary
Under elevated ozone, ascorbate use in ozone scavenging exceeded use by oxidases.
- Taxon
- Betula pendulaBetula pendulat0
- Outcome
- ASC use in O3 scavenginge0
- Direction
- highere0
- Comparator
- oxidasese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Under elevated O3, ASC use in O3 scavenging was higher than by oxidases.”
t0“Components of apoplastic ascorbate use in Betula pendula leaves exposed to CO2 and O3 enrichment”
Claim · model-written summary
Ozone did not depress ascorbate redox state.
- Taxon
- Betula pendulaBetula pendulat0
- Treatment
- O3e0
- Outcome
- redox state of ASCe0
- Direction
- not depressede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The redox state of ASC was not depressed by O3; there was no leaf injury.”
t0“Components of apoplastic ascorbate use in Betula pendula leaves exposed to CO2 and O3 enrichment”
Claim · model-written summary
No leaf injury was observed under ozone exposure.
- Taxon
- Betula pendulaBetula pendulat0
- Outcome
- leaf injurye0
- Direction
- noe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The redox state of ASC was not depressed by O3; there was no leaf injury.”
t0“Components of apoplastic ascorbate use in Betula pendula leaves exposed to CO2 and O3 enrichment”
Claim · model-written summary
The birch cell wall, plasmalemma and cytosol system maintained apoplastic ascorbate redox status without restricting ozone uptake through stomatal closure.
Verbatim
e0“The cell wall/plasmalemma/cytosol system in birch had sufficient capacity to maintain ASC redox status in the apoplast, without necessity to restrict O3 uptake by stomatal closure.”
The same questions in other papers
ozone · physiology: gas exchange · Betula pendula (white birch)Results differ
6 papers in the same direction as this paper · 1 in the opposite direction
- negative
- positive
- negative
4 papers more in this group
See all 8 papers →ozone · molecular: metabolites · Betula pendula (white birch)Positive and negative results
2 in the opposite direction
- negative
- negative
Claims are grouped by organism, treatment and what was measured or targeted. A paper counts as positive when any of its claims in the group is positive.