Hormonal control of ion channel gating
Blatt M. R., Thiel G. (1993)
Annu. Rev. Plant Physiol. Mol. Biol. 44: 543–567 – https://doi.org/10.1146/annurev.pp.44.060193.002551 –
https://www.annualreviews.org/doi/10.1146/annurev.pp.44.060193.002551
Tag: Thiel G.
Exo- and endocytosis is an essential process in stomatal guard cell functioning
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Exo-和内吞作用是气孔保卫细胞功能中的重要过程
A exo e endocitose são processos essenciais para o funcionamento das células-guarda estomáticas.
La exo y endocitosis son procesos esenciales en el funcionamiento de las células guardianas estomáticas.
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Guard cells undergo constitutive and pressure-driven membrane turnover
Meckel T., Hurst A. C., Thiel G., Homann U. (2005)
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Protoplasma. 226(1-2): 23-29 – doi: 10.1007/s00709-005-0106-6 – Epub 2005 Oct 20 -PMID: 16231098 –
https://pubmed.ncbi.nlm.nih.gov/16231098/
Abstract
During stomatal movement, guard cells undergo large and reversible changes in cell volume and consequently surface area. These alterations in surface area require addition and removal of plasma membrane material. How this is achieved is largely unknown. Here we summarize recent studies of membrane turnover in guard cells using electrophysiology and fluorescent imaging techniques. The results implicate that membrane turnover in guard cells and most likely in plant cells in general is sensitive to changes in membrane tension. We suggest that this provides a mechanism for the adaptation of surface area of guard cells to osmotically driven changes in cell volume. In addition, guard cells also exhibit constitutive membrane turnover. Constitutive and pressure-driven membrane turnover were found to be associated with addition and removal of K+ channels. This implies that some of the exo- and endocytic vesicles carry K+ channels. Together the results demonstrate that exo- and endocytosis is an essential process in guard cell functioning.
Voltage control and membrane transport in stomatal guard cells
Membrane transport in stomatal guard cells: the importance of voltage control
by Thiel G., MacRobbie E. A., Blatt M. R. (1992)
Botany School, University of Cambridge, Cambridge, England
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In Journal of Membrance Biology 126: 1-18 – https://doi.org/10.1007/BF00233456 –
https://link.springer.com/article/10.1007/BF00233456
Abstract
Potassium uptake and export in the resting conditions and in response to the phytohormone abscisic acid (ABA) were examined under voltage clamp in guard cells of Vicia faba L. In 0.1 mm external K+ (with 5 mm Ca2+-HEPES, pH 7.4) two distinct transport states could be identified based on the distribution of the free-running membrane voltage(V M ) data in conjunction with the respective I-V and G-V relations. One state was dominated by passive diffusion (mean V M = −143± 4 mV), the other (mean V M = −237± 10 mV) exhibited an appreciable background of primary H+ transport activity. In the presence of pump activity the free-running membrane voltage was negative of the respective K+equilibrium potential (EK+), in 3 and 10 mm external K+. In these cases V M was also negative of the activation voltage for the inward rectifying K+ current, thus creating a strong bias for passive K+ uptake through inward-rectifying K+ channels. In contrast, when pump activity was absent V M was situated positive of EK+ and cells revealed a bias for K+ efflux. Occasionally spontaneous voltage transitions were observed during which cells switched between the two states. Rapid depolarizations were induced in cells with significant pump activity upon adding 10 μm ABA to the medium. These depolarizations activated current through outward-rectifying K+ channels which was further amplified in ABA by a rise in the ensemble channel conductance. Current-voltage characteristics recorded before and during ABA treatments revealed concerted modulations in current passage through at least four distinct transport processes, results directly comparable to one previous study (Blatt, M.R., 1990, Planta 180:445) carried out with guard cells lacking detectable primary pump activity. Comparative analyses of guard cells in each case are consistent with depolarizations resulting from the activation of an inward-going, as yet unidentified current, rather than an ABA-induced fall in H+-ATPase output. Also observed in a number of cells was an inward-directed current which activated in ABA over a narrow range of voltages positive of -150 mV; this and additional features of the current suggest that it may reflect the ABA-dependent activation of an anion channel previously characterized in Vicia guard cell protoplasts, but rule out its function as the primary mechanism for initial depolarization. The analyses also yield indirect evidence for a rise in cytoplasmic Ca2+ activity in ABA, as well as for a K+ current distinct from the dominant inward and outward-rectifying K+ channels, but neither support nor discount a role for Ca2+influx in depolarizing the membrane. A striking similarity was found for the modulation of inward currents either in response to ABA or after spontaneous depolarizations. This renders the possibility of an agonist (i.e., ABA) activated Ca2+ current across the plasma membrane as trigger for the voltage transitions unlikely.
Endocytosis of small vesicles into the cytoplasm is the obligatory process in stomata
Osmotically evoked shrinking of guard-cell protoplasts causes vesicular retrieval of plasma membrane into the cytoplasm.
, , . (2000)
- Ulrich Kubitscheck
- Ulrike Homann
- Gerhard Thiel
in Planta 210: 423–431. –
http://link.springer.com/article/10.1007%2FPL00008151
Abstract
The dye FM1-43 was used alone or in combination with measurements of the membrane capacitance (Cm) to monitor membrane changes in protoplasts from Vicia faba L. guard cells. Confocal images of protoplasts incubated with FM1-43 (10 μM) at constant ambient osmotic pressure (πo) revealed in confocal images a slow internalisation of FM1-43-labelled membrane into the cytoplasm.
As a result of this process the relative fluorescence intensity of the cell interior (fFM,i) increased with reference to the total fluorescence (fFM,t) by 7.4 × 10−4 min−1.
This steady internalisation of dye suggests the occurrence of constitutive endocytosis under constant osmotic pressure. Steady internalisation of FM1-43 labelled membrane caused a prominent staining of a ring-like structure located beneath the plasma membrane. Abrupt elevation of πo by 200 mosmol kg−1 caused, over the first minutes of incubation, a rapid internalisation of FM1-43 fluorescence into the cytoplasm concomitant with a decrease in cell perimeter. Within the first 5 min the cell perimeter decreased by 7.9%. Over the same time fFM,i/fFM,t increased by 0.13, reflecting internalisation of fluorescent label into the cytoplasm.
Combined measurements of Cm and total fluorescence of a protoplast (fFM,p) showed that an increase in πo evoked a decrease in Cm but no change in fFM,p. This means that surface contraction of the protoplast is due to retrieval of excess membrane from the plasma membrane and internalisation into the cytoplasm.
Further inspection of confocal images revealed that protoplast shrinking was only occasionally associated with internalisation of giant vesicles (median diameter 2.7 μm) with FM1-43-labelled membrane. But, in all cases, osmotic contraction was correlated with a diffuse distribution of FM1-43 label throughout the cytoplasm.
From this, we conclude that endocytosis of small vesicles into the cytoplasm is the obligatory process by which cells accommodate an osmotically driven decrease in membrane surface area.
About guard cell protoplasts
Unitary exocytotic and endocytotic events in guard cell protoplasts during osmotically driven Volume changes
, . (1999)
in FEBS Letters 460: 495–499. –
http://www.ncbi.nlm.nih.gov/pubmed/10556524
Abstract
Osmotically driven swelling and shrinking of guard-cell protoplasts (GCPs) requires adjustment of surface area which is achieved by addition and removal of plasma membrane material.
To investigate the mechanism for adaptation of surface area we have used patch-clamp capacitance measurements. The recorded membrane capacitance (C(m)) trace of swelling and shrinking GCPs occasionally revealed discrete upward and downward deflecting capacitance steps, respectively, with a median value of about 2 fF.
The observed capacitance steps resulted from the fusion and fission of single vesicles with a diameter of around 300 nm.
We conclude that exo- and endocytosis of these vesicles accommodate for osmotically driven surface area changes in GCPs.
K+ channels of stomatal guard cells and auxin
K+ channels of stomatal guard cells: Bimodal control of the K+inward-rectifier evoked by auxin.
by Blatt M.R., Thiel G. (1994)
in Plant J. 5: 55–68
[PubMed]
http://www.ncbi.nlm.nih.gov/pubmed/8130798
Abstract
The influence of the auxins indole-3-acetic acid (IAA) and 1-napthylene acetic acid (NAA) on K+ channels and their control was examined in stomatal guard cells of Vicia faba L.
Intact guard cells were impaled with multibarrelled microelectrodes to record membrane potentials and to monitor K+ channel currents under voltage clamp during exposures to 0.1-100 microM IAA and NAA. Following impalements, challenge with either IAA or NAA in the presence of 10 mM KCl resulted in the concerted modulation of at least four different currents with distinct kinetic characteristics and concentration dependencies.
Equivalent concentrations of benzoic acid were wholly without effect. Most striking, current carried by inward-rectifying K+ channels (IK,in) exhibited a bimodal response to both IAA and NAA which was reversed on washing the auxins from the bathing medium. The steady-state current was augmented 1.3- to 2-fold at concentrations between 0.1 and 10 microM and antagonized at concentrations near 30 microM and above.
Auxin agonism of IK,in was time- and voltage-independent. By contrast, IK,in inactivation at the higher auxin concentrations was marked by a voltage-dependence and slowing of the kinetics for current activation. Inactivation of IK,in by the auxins was relieved when cytoplasmic pH (pHi) was clamped near 7.0 in the presence of 30 mM Na(+)-butyrate. In addition to the control of IK,in, current carried by a second class of (outward-rectifying) K+ channels rose in a monotonic and largely voltage-independent manner with auxin concentrations about 10 microM and above, and IAA and NAA also activated an inward-going current with a voltage dependence characteristic of guard cell anion channels.
Further changes in background current were consistent with a limited activation of the H(+)-ATPase. Over the concentration range examined, the auxins evoked membrane hyperpolarizations and depolarizations of up to +/- 12-19 mV, depending on the free-running membrane potential prevailing before auxin additions.
Prolonging exposures to 100 microM auxin beyond 3-5 min frequently elicited rapid transitions to voltages near EK as well as regenerative action potentials. However, in every case the voltage response was a predictable consequence of auxin action on the K+ channels and, at 100 microM auxin, on the anion current.(ABSTRACT TRUNCATED AT 400 WORDS).
PLANT STOMATA ENCYCLOPEDIA 