Abstract
Closing of stomatal pores in the leaf epidermis of higher plants is mediated by long-term release of potassium and the anions chloride and malate from guard cells and by parallel metabolism of malate. Previous studies have shown that slowly activating anion channels in the plasma membrane of guard cells can provide a major pathway for anion efflux while also controlling K+ efflux during stomatal closing: Anion efflux produces depolarization of the guard cell plasma membrane that drives K+ efflux required for stomatal closing. The patch-clamp technique was applied to Vicia faba guard cells to determine the permeability of physiologically significant anions and halides through slow anion channels to assess the contribution of these anion channels to anion efflux during stomatal closing. Permeability ratio measurements showed that all tested anions were permeable with the selectivity sequence relative to Cl- of NO3- > Br- > F- ~ Cl- ~ I- > malate. Large malate concentrations in the cytosol (150 mM) produced a slow down-regulation of slow anion channel currents. Single anion channel currents were recorded that correlated with whole-cell anion currents. Single slow anion channels confirmed the large permeability ratio for nitrate over chloride ions. Furthermore, single-channel studies support previous indications of multiple conductance states of slow anion channels, suggesting cooperativity among anion channels. Anion conductances showed that slow anion channels can mediate physiological rates of Cl- and initial malate efflux required for mediation of stomatal closure. The large NO3- permeability as well as the significant permeabilities of all anions tested indicates that slow anion channels do not discriminate strongly among anions. Furthermore, these data suggest that slow anion channels can provide an efficient pathway for efflux of physiologically important anions from guard cells and possibly also from other higher plant cells that express slow anion channels.
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Claims 10
Claim · model-written summary
All tested anions permeated slow channels in the stated selectivity sequence.
- Taxon
- Vicia faba
Vicia fabat0 - Outcome
- selectivity sequence relative to Cl- of NO3- > Br- > F- ~ Cl- ~ I- > malatee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“all tested anions were permeable with the selectivity sequence relative to Cl- of NO3- > Br- > F- ~ Cl- ~ I- > malate”
t0“Vicia faba guard cells”
Claim · model-written summary
Cytosolic malate at 150 mM slowly downregulated slow anion channel currents.
- Taxon
- Vicia fabaVicia fabat0
- Treatment
- malate concentrations in the cytosol (150 mM)e0
- Outcome
- slow anion channel currentse0
- Direction
- down-regulatione0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Large malate concentrations in the cytosol (150 mM) produced a slow down-regulation of slow anion channel currents”
t0“Vicia faba guard cells”
Claim · model-written summary
Single anion channel currents correlated with whole-cell currents.
- Taxon
- Vicia fabaVicia fabat0
- Outcome
- Single anion channel currentse0
- Comparator
- whole-cell anion currentse0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Single anion channel currents were recorded that correlated with whole-cell anion currents”
t0“Vicia faba guard cells”
Claim · model-written summary
Single channels confirmed high nitrate permeability relative to chloride.
- Taxon
- Vicia fabaVicia fabat0
- Outcome
- permeability ratio for nitrate over chloride ionse0
- Direction
- largee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Single slow anion channels confirmed the large permeability ratio for nitrate over chloride ions”
t0“Vicia faba guard cells”
Claim · model-written summary
Single-channel studies supported multiple conductance states.
- Taxon
- Vicia fabaVicia fabat0
- Outcome
- multiple conductance states of slow anion channelse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“single-channel studies support previous indications of multiple conductance states of slow anion channels”
t0“Vicia faba guard cells”
Claim · model-written summary
Multiple channel conductance states suggested cooperativity.
- Taxon
- Vicia fabaVicia fabat0
- Outcome
- cooperativity among anion channelse0
- Qualifier
- multiple conductance states of slow anion channelse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“multiple conductance states of slow anion channels, suggesting cooperativity among anion channels”
t0“Vicia faba guard cells”
Claim · model-written summary
Slow anion channels could mediate physiological chloride efflux rates.
- Taxon
- Vicia fabaVicia fabat0
- Outcome
- physiological rates of Cl-e0
- Qualifier
- slow anion channelse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“slow anion channels can mediate physiological rates of Cl- and initial malate efflux required for mediation of stomatal closure”
t0“Vicia faba guard cells”
Claim · model-written summary
Slow anion channels could mediate initial malate efflux for stomatal closure.
- Taxon
- Vicia fabaVicia fabat0
- Outcome
- initial malate effluxe0
- Qualifier
- slow anion channelse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“slow anion channels can mediate physiological rates of Cl- and initial malate efflux required for mediation of stomatal closure”
t0“Vicia faba guard cells”
Claim · model-written summary
Slow anion channels did not strongly discriminate among anions.
- Taxon
- Vicia fabaVicia fabat0
- Outcome
- discriminate strongly among anionse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“slow anion channels do not discriminate strongly among anions”
t0“Vicia faba guard cells”
Claim · model-written summary
Slow anion channels may provide efficient anion efflux from guard cells.
- Taxon
- Vicia fabaVicia fabat0
- Outcome
- efflux of physiologically important anions from guard cellse0
- Qualifier
- slow anion channelse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“slow anion channels can provide an efficient pathway for efflux of physiologically important anions from guard cells”
t0“Vicia faba guard cells”