Abstract
Many signal-transduction processes in higher plant cells have been suggested to be triggered by signal-induced opening of Ca2+ channels in the plasma membrane. However, direct evidence for activation of plasma-membrane Ca2+ channels by physiological signals in higher plants has not yet been obtained. In this context, several lines of evidence suggest that Ca2+ flux into the cytosol of guard cells is a major factor in the induction of stomatal closing by abscisic acid (ABA). ABA closes stomatal pores, thereby reducing transpirational loss of water by plants under drought conditions. To directly investigate initial events in ABA-induced signal transduction in guard cells, we devised an experimental approach that allows simultaneous photometric measurements of cytosolic Ca2+ and patch-clamp recordings of ion currents across the plasma membrane of single Vicia faba guard cells. Using this approach, we found that the resting cytosolic Ca2+ concentration was 0.19 +/- 0.09 microM (n = 19). In responsive guard cells, external exposure to ABA produced transient repetitive increases in the cytosolic free Ca2+ concentration. These Ca2+ transients were accompanied by concomitantly occurring increases in an inward-directed ion current. Depolarization of the membrane terminated both repetitive elevations in cytosolic Ca2+ and inward-directed ion currents, suggesting that ABA-mediated Ca2+ transients were produced by passive influx of Ca2+ from the extracellular space through Ca2(+)-permeable channels. Detailed voltage-clamp measurements revealed that ABA-activated ion currents could be reversed by depolarizations more positive than -10 mV. Interestingly, reversal potentials of ABA-induced currents show that these currents are not highly Ca2(+)-selective, thereby permitting permeation of both Ca2+ and K+. These results provide direct evidence for ABA activation of Ca2(+)-permeable ion channels in the plasma membrane of guard cells. ABA-activated ion channels allow repetitive elevations in the cytosolic Ca2+ concentration, which, in turn, can modulate cellular responses promoting stomatal closure.
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Claims 10
Claim · model-written summary
Resting guard-cell cytosolic calcium was 0.19 +/- 0.09 microM.
- Taxon
- Vicia faba
Vicia fabat0 - Organ / stage
- guard cellst0
- Outcome
- resting cytosolic Ca2+ concentratione0
- Value
- 0.19 +/- 0.09 microMe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the resting cytosolic Ca2+ concentration was 0.19 +/- 0.09 microM (n = 19)”
t0“Vicia faba guard cells”
Claim · model-written summary
ABA exposure caused transient repetitive increases in cytosolic free calcium in responsive guard cells.
- Taxon
- Vicia fabaVicia fabat0
- Organ / stage
- guard cellse0
- Treatment
- external exposure to ABAe0
- Outcome
- cytosolic free Ca2+ concentratione0
- Direction
- increasese0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In responsive guard cells, external exposure to ABA produced transient repetitive increases in the cytosolic free Ca2+ concentration.”
t0“Vicia faba guard cells”
Claim · model-written summary
Calcium transients coincided with increases in inward ion current.
- Taxon
- Vicia fabaVicia fabat0
- Compound
- Ca2+e0
- Outcome
- inward-directed ion currente0
- Direction
- increasese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“These Ca2+ transients were accompanied by concomitantly occurring increases in an inward-directed ion current.”
t0“Vicia faba guard cells”
Claim · model-written summary
Membrane depolarization terminated repetitive cytosolic calcium elevations.
- Taxon
- Vicia fabaVicia fabat0
- Treatment
- Depolarization of the membranee0
- Outcome
- repetitive elevations in cytosolic Ca2+e0
- Direction
- terminatede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Depolarization of the membrane terminated both repetitive elevations in cytosolic Ca2+ and inward-directed ion currents”
t0“Vicia faba guard cells”
Claim · model-written summary
Membrane depolarization terminated inward ion currents.
- Taxon
- Vicia fabaVicia fabat0
- Treatment
- Depolarization of the membranee0
- Outcome
- inward-directed ion currentse0
- Direction
- terminatede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Depolarization of the membrane terminated both repetitive elevations in cytosolic Ca2+ and inward-directed ion currents”
t0“Vicia faba guard cells”
Claim · model-written summary
The authors infer ABA calcium transients arise from passive extracellular calcium influx through permeable channels.
- Taxon
- Vicia fabaVicia fabat0
- Outcome
- ABA-mediated Ca2+ transientse0
- Qualifier
- passive influx of Ca2+ from the extracellular space through Ca2(+)-permeable channelse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“ABA-mediated Ca2+ transients were produced by passive influx of Ca2+ from the extracellular space through Ca2(+)-permeable channels”
t0“Vicia faba guard cells”
Claim · model-written summary
ABA activated currents reversed at depolarizations above -10 mV.
- Taxon
- Vicia fabaVicia fabat0
- Treatment
- depolarizations more positive than -10 mVe0
- Outcome
- ABA-activated ion currents could be reversede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“ABA-activated ion currents could be reversed by depolarizations more positive than -10 mV”
t0“Vicia faba guard cells”
Claim · model-written summary
ABA-induced currents were not highly calcium selective and permitted calcium and potassium permeation.
- Taxon
- Vicia fabaVicia fabat0
- Outcome
- not highly Ca2(+)-selective, thereby permitting permeation of both Ca2+ and K+e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“ABA-induced currents show that these currents are not highly Ca2(+)-selective, thereby permitting permeation of both Ca2+ and K+”
t0“Vicia faba guard cells”
Claim · model-written summary
ABA activated calcium permeable channels in the guard-cell plasma membrane.
- Taxon
- Vicia fabaVicia fabat0
- Organ / stage
- guard cellse0
- Treatment
- ABAe0
- Outcome
- activation of Ca2(+)-permeable ion channelse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“ABA activation of Ca2(+)-permeable ion channels in the plasma membrane of guard cells”
t0“Vicia faba guard cells”
Claim · model-written summary
The authors infer calcium elevations can modulate responses that promote stomatal closure.
- Taxon
- Vicia fabaVicia fabat0
- Outcome
- cellular responses promoting stomatal closuree0
- Qualifier
- repetitive elevations in the cytosolic Ca2+ concentratione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“repetitive elevations in the cytosolic Ca2+ concentration, which, in turn, can modulate cellular responses promoting stomatal closure”
t0“Vicia faba guard cells”
The same questions in other papers
(+)-abscisic acid · molecular: metabolites · Vicia faba (faba bean)Results differ
4 papers in the same direction as this paper · 3 in the opposite direction
- no effect
- no effect
- positive
4 papers more in this group
See all 8 papers →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.