Stomatal closure was found to be accompanied by an initial hyperpolarization and cytosolic acidification of subsidiary cells

Cell type-specific regulation of ion channels within the maize stomatal complex

Mumm P., Wolf T., Fromm J., Roelfsema M. R. G., Marten I. (2011)

Patrick Mumm, Thomas Wolf, Jörg Fromm, M Rob G Roelfsema, Irene Marten,

Plant Cell Physiol 52: 1365–1375 – doi: 10.1093/pcp/pcr082 – Epub 2011 Jun 20 –

https://pubmed.ncbi.nlm.nih.gov/21690176/

Abstract

The stomatal complex of Zea mays is composed of two pore-forming guard cells and two adjacent subsidiary cells. For stomatal movement, potassium ions and anions are thought to shuttle between these two cell types. As potential cation transport pathways, K(+)-selective channels have already been identified and characterized in subsidiary cells and guard cells. However, so far the nature and regulation of anion channels in these cell types have remained unclear. In order to bridge this gap, we performed patch-clamp experiments with subsidiary cell and guard cell protoplasts. Voltage-independent anion channels were identified in both cell types which, surprisingly, exhibited different, cell-type specific dependencies on cytosolic Ca(2+) and pH. After impaling subsidiary cells of intact maize plants with microelectrodes and loading with BCECF [(2′,7′-bis-(2-carboxyethyl)-5(and6)carboxyflurescein] as a fluorescent pH indicator, the regulation of ion channels by the cytosolic pH and the membrane voltage was further examined. Stomatal closure was found to be accompanied by an initial hyperpolarization and cytosolic acidification of subsidiary cells, while opposite responses were observed during stomatal opening. Our findings suggest that specific changes in membrane potential and cytosolic pH are likely to play a role in determining the direction and capacity of ion transport in subsidiary cells.

AtALMT12 represents an R-type anion channel required for stomatal movement

 

 

AtALMT12 represents an R-type anion channel required for stomatal movement in Arabidopsis guard cells

by Meyer S., Mumm P., Imes D., Endler A., Weder B., Al-Rasheid K. A. S., Geiger D, Marten I, Martinoia E, Hedrich R. (2010)

Stefan Meyer, Blood Donation Center Zurich, Switserland

Patrick Mumm, University of Wuerzburg, Germany

Dennis Imes, Anne Endler, Barbara Weder,

Khaled A S AL-Rasheid, King Saud University, Riyadh, Saudi Arabia

Dietmar Geiger, University of Wuerzburg, Germany

Irene Marten, University of Wuerzburg, Germany

Enrico Martinoia, University of Zurich, Switserland

Rainer Hedrich, University of Wuerzburg, Germany

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in Plant J. 63: 1054–1062. – doi: 10.1111/j.1365-313X.2010.04302.x –

https://www.ncbi.nlm.nih.gov/pubmed/20626656

Abstract

Stomatal pores formed by a pair of guard cells in the leaf epidermis control gas exchange and transpirational water loss. Stomatal closure is mediated by the release of potassium and anions from guard cells.

Anion efflux from guard cells involves slow (S-type) and rapid (R-type) anion channels. Recently the SLAC1 gene has been shown to encode the slow, voltage-independent anion channel component in guard cells. In contrast, the R-type channel still awaits identification.

Here, we show that AtALMT12, a member of the aluminum activated malate transporter family in Arabidopsis, represents a guard cell R-type anion channel. AtALMT12 is highly expressed in guard cells and is targeted to the plasma membrane.

Plants lacking AtALMT12 are impaired in dark- and CO₂ -induced stomatal closure, as well as in response to the drought-stress hormone abscisic acid. Patch-clamp studies on guard cell protoplasts isolated from atalmt12 mutants revealed reduced R-type currents compared with wild-type plants when malate is present in the bath media. Following expression of AtALMT12 in Xenopus oocytes, voltage-dependent anion currents reminiscent to R-type channels could be activated.

In line with the features of the R-type channel, the activity of heterologously expressed AtALMT12 depends on extracellular malate. Thereby this key metabolite and osmolite of guard cells shifts the threshold for voltage activation of AtALMT12 towards more hyperpolarized potentials.

R-Type channels, like voltage-dependent cation channels in nerve cells, are capable of transiently depolarizing guard cells, and thus could trigger membrane potential oscillations, action potentials and initiate long-term anion and K(+) efflux via SLAC1 and GORK, respectively.

Ion channels within the maize stomata

 

Cell type-specific regulation of ion channels within the maize stomatal complex.

by Mumm P., Wolf T., Fromm J., Roelfsema M. R. G., Marten I. (2011)

1. Patrick Mumm
2. Thomas Wolf
3. Jörg Fromm
4. M. Rob G. Roelfsema
5. Irene Marten

in Plant and Cell Physiology 52 : 1365–1375. – doi: 10.1093/pcp/pcr082 –

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text | Google Scholar

http://pcp.oxfordjournals.org/content/52/8/1365

Abstract

The stomatal complex of Zea mays is composed of two pore-forming guard cells and two adjacent subsidiary cells.

For stomatal movement, potassium ions and anions are thought to shuttle between these two cell types. As potential cation transport pathways, K⁺-selective channels have already been identified and characterized in subsidiary cells and guard cells. However, so far the nature and regulation of anion channels in these cell types have remained unclear.

In order to bridge this gap, we performed patch–clamp experiments with subsidiary cell and guard cell protoplasts. Voltage-independent anion channels were identified in both cell types which, surprisingly, exhibited different, cell-type specific dependencies on cytosolic Ca²⁺ and pH. After impaling subsidiary cells of intact maize plants with microelectrodes and loading with

BCECF [(2′,7′-bis-(2-carboxyethyl)-5(and6)carboxyflurescein] as a fluorescent pH indicator, the regulation of ion channels by the cytosolic pH and the membrane voltage was further examined.

Stomatal closure was found to be accompanied by an initial hyperpolarization and cytosolic acidification of subsidiary cells, while opposite responses were observed during stomatal opening.

Our findings suggest that specific changes in membrane potential and cytosolic pH are likely to play a role in determining the direction and capacity of ion transport in subsidiary cells.