Abstract
The effect of ABA on the membrane potential of barley (Hordeum vulgare cv. Himalaya) aleurone protoplasts was studied by measuring the distribution of the lipophilic cation tetraphenylphosphonium (TPP+). The resting membrane potential (Em) according to our measurements with TPP+ is about −53 mV and is in agreement with membrane potential values as measured with intracellular microelectrodes (about −55 mV). The TPP+-measurements could demonstrate a clear dependence of the resting Em on the external pH (pHe). Stimulation of the protoplasts with ABA induced a transient hyperpolarization of the membrane to −62 mV as measured with TPP+. The hyperpolarization was ABA-concentration dependent. Inhibition of the H+-ATPases with the specific proton pump inhibitors diethylstilbestrol (DES) or Micanozole effectively prevented hyperpolarization. This indicates that the hyperpolarization is consistent with the activation of plasma membrane H+-ATPases. The K+-inward rectifier inhibitor BaCl2 was able to prolong the hyperpolarization. This result suggests that the hyperpolarization causes the opening of K+-channels. The ABA-induced proton-pump activation may be involved in ABA-induced gene-expression, as DES was able to inhibit this gene expression. BaCl2 did only show a slight inhibitory effect on ABA-induced gene-expression.
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Claims 11
Claim · model-written summary
Resting membrane potential was about −53 mV, agreeing with microelectrode measurements of about −55 mV.
Not reportedTaxon
Verbatim
e0“The resting membrane potential (Em) according to our measurements with TPP+ is about −53 mV and is in agreement with membrane potential values as measured with intracellular microelectrodes (about −55 mV).”
Claim · model-written summary
Resting membrane potential depended on external pH.
Not reportedTaxonDirection
Verbatim
e0“The TPP+-measurements could demonstrate a clear dependence of the resting Em on the external pH (pHe).”
Claim · model-written summary
ABA transiently hyperpolarized the membrane to −62 mV.
Not reportedTaxonComparator
Verbatim
e0“Stimulation of the protoplasts with ABA induced a transient hyperpolarization of the membrane to −62 mV as measured with TPP+.”
Claim · model-written summary
Hyperpolarization depended on ABA concentration.
Not reportedTaxonDirection
Verbatim
e0“The hyperpolarization was ABA-concentration dependent.”
Claim · model-written summary
DES prevented hyperpolarization.
Not reportedTaxonComparator
Verbatim
e0“Inhibition of the H+-ATPases with the specific proton pump inhibitors diethylstilbestrol (DES) or Micanozole effectively prevented hyperpolarization.”
Claim · model-written summary
Micanozole prevented hyperpolarization.
Not reportedTaxonComparator
Verbatim
e0“Inhibition of the H+-ATPases with the specific proton pump inhibitors diethylstilbestrol (DES) or Micanozole effectively prevented hyperpolarization.”
Claim · model-written summary
Hyperpolarization was interpreted as consistent with H+-ATPase activation.
Not reportedTaxon
Verbatim
e0“This indicates that the hyperpolarization is consistent with the activation of plasma membrane H+-ATPases.”
Claim · model-written summary
BaCl2 prolonged hyperpolarization.
Not reportedTaxonComparator
Verbatim
e0“The K+-inward rectifier inhibitor BaCl2 was able to prolong the hyperpolarization.”
Claim · model-written summary
Hyperpolarization was suggested to open K+ channels.
Not reportedTaxon
Verbatim
e0“This result suggests that the hyperpolarization causes the opening of K+-channels.”
Claim · model-written summary
DES inhibited ABA-induced gene expression.
Not reportedTaxonComparator
Verbatim
e0“The ABA-induced proton-pump activation may be involved in ABA-induced gene-expression, as DES was able to inhibit this gene expression.”
Claim · model-written summary
BaCl2 had a slight inhibitory effect on ABA-induced gene expression.
Not reportedTaxonComparator
Verbatim
e0“BaCl2 did only show a slight inhibitory effect on ABA-induced gene-expression.”