Stomata

M Rob G Roelfsema, University of Würzburg, Würzburg, Germany
Rainer Hedrich, University of Würzburg, Würzburg, Germany

Published online: March 2009

DOI: 10.1002/9780470015902.a0002075.pub2

Stomata are small adjustable pores on the surface of aerial plant tissues. The pores open to facilitate uptake of carbon dioxide and close to limit the loss of water. Consistent with this function, stomata open in the light to enable photosynthesis and close during drought. Stomatal movements are forced by changes in the volume of two guard cells that are positioned on either side of the pore. During stomatal opening, guard cells accumulate potassium salts, causing an osmotically driven uptake of water. Owing to the influx of water the guard cells swell and bend, thereby pushing each other apart and creating an open pore in the middle. Various environmental signals, such as light, carbon dioxide and humidity, influence the ion-transport machinery within the guard cell and thus alter stomatal movement. Because of their role in regulating carbon dioxide uptake and transpiration of water, stomata are likely to play a key role in the adaption of plants to the anticipated global warming.

Key concepts

  • Stomata are small adjustable pores in the leave surface that enable gas exchange.
  • Open stomata enable the uptake of carbon dioxide for photosynthesis, while closure prevents excessive loss of water during drought.
  • During evolution, stomata enabled plants to survive in dry environments.
  • Cell-to-cell signalling controls the development of stomata in the leaf surface.
  • Stomatal movements are forced by two guard cells, surrounding the pore.
  • Guard cells cause stomata opening through osmotically driven swelling, based on the uptake of K+ salts.
  • Environmental signals regulate ion transport in guard cells.
  • Guard cells sense light with blue light-sensitive phototropins as well as through changes in the intercellular carbon dioxide concentration.
  • Drought acts on guard cells via release of the stress hormone abscisic acid.
  • Stomata are likely to play an important role in the adaption of plants to predicted global changes.

Keywords: stomata; guard cells; ion transport; light and drought sensing; global change; agriculture

Figure 1. Images of stomata obtained by scanning electron microscopy (a) or transmitted light microscopy (b and c). (a) Leaf surface of Nicotiana alamata consisting of jigsaw-like epidermal pavement cells (marked #1) surrounding stomatal pores (#2) and leaf hairs (trichomes, #3). Image used with permission of L Howard, Dartmouth College NH USA, available at http://remf.dartmouth.edu/images/botanicalLeafSEM/index.html from (b) Stoma of tobacco (N. tabacum cv. Samsun). The pore (marked #1) is surrounded by two kidney-shaped guard cells (#2). Note the round structure in the middle of the cells which contains the nucleus and green chloroplasts at the periphery of the cells. (c) Stomatal complex of corn (Zea mais), the pore (marked #1) is surrounded by two dumbbell-shaped guard cells (#2) that are in turn flanked by two companion cells (#3). Image obtained from P Mumm, University of Würzburg, Germany.
Figure 2. Development of guard cells from precursor cells in stomatal cell lineage in Arabidopsis. The first precursor, the meristemoid mother cell produces a smaller cell, the meristemoid via an asymmetrical division. The meristemoid develops into a guard mother cell, whereas its sister cell can form additional meristemoids through further asymmetrical divisions. The guard mother cell undergoes a single symmetrical division to form two guard cells. Redrawn with permission, after Geisler MJ, deppong DO, Nadeau JA and Sack FD (2003) Stomatal neighbor cell polarity and division in Arabidopsis. Planta 216: 571–579, Figure 1a.
Figure 3. Three-dimensional representation of guard cells in closed (left picture) and open (right picture) stomata. Guard cells force stomatal opening by an osmotically driven increase of their cell volume. The increase in volume causes the guard cells to bend and change the shape of their cross section from a flat oval, to a circle. From Roelfsema and Hedrich (2005).
Figure 4. Schematic representation of ion transport across the plasma membrane and vacuolar membrane leading to stomatal movement. The plasma membrane is mainly energized by a proton (H+) pumping ATPase causing a H+ gradient as well as an electrical charge difference (membrane potential) across the plasma membrane (marked #1). The membrane potential can drive an influx of potassium (K+) through K+-uptake ion channels (#2). Anions are taken up into the cytosol through co-transport with H+ (#3). In addition, malate2– is synthesized (#4) from carbon dioxide and phosphoenolpyruvate (PEP) by the PEP carboxilase. The ions are further transported into the vacuole, in which the V-type H+-ATPase (#5) generates an H+ gradient and vacuolar membrane potential. Anion transport into the vacuole, through anion channels, is supported by the electrical potential (#6), whereas K+ uptake requires H+ cotransport (#7). Stomatal closure is associated with the efflux of K+ from the vacuole (#8), which also degrades the membrane potential. Owing to the depolarized membrane potential anions are released into the cytosol (#9). At the plasma membrane, the activation of anion channels leads to an efflux of anions (#10) into the guard cell wall and depolarization. Owing to the depolarized plasma membrane, K+ is extruded trough K+-efflux channels (#11). From Roelfsema and Hedrich (2005).
Figure 5. Light-induced electrical responses of guard cells. (a) Membrane potential (electrical charge difference) recording of the guard cell plasma membrane with a micro electrode. The measurement was started in darkness; switching on light caused a reversible change of the membrane potential from –55 to –110 mV. This change in membrane potential alters the direction of K+ transport across the plasma membrane, since the equilibrium potential for K+ approximates –80 mV. In the dark the membrane potential of –55 mV allows the efflux of K+, whereas the value of –110 mV enables K+ uptake through ion channels. Data from Roelfsema MRG, Steinmeyer R, Staal M and Hedrich R (2001). Single guard cell recordings in intact plants: light-induced hyperpolarization of the plasma membrane. Plant Journal 26:1–13. (b) Electrical current changes at the plasma membrane triggered by blue light. A Vicia faba guard cell was clamped with a double barrelled electrode to –100 mV. Switching on blue light caused a transient outward current, which was reversed after switching off blue light. Note that the current trace is interrupted by periods at which the membrane potential was altered, as indicated by diamonds. Data from Marten et al. (2007a). (c) Schematic representation of the regulation of ion transport by phototropins in guard cells. Two types of phototropins (PHOT1 and PHOT2) are activated by blue light and in turn stimulate plasma membrane H+-ATPases and inhibit S-type anion channels. Both changes in the activity of these transporters cause an increase in outward current as shown in (b).
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 Further Reading
    Hetherington AM and Woodward FI (2003) The role of stomata in sensing and driving environmental change. Nature 424: 901–908.
    Roelfsema MRG and Hedrich R (2005) In the light of stomtal opening: new insights into “the Watergate”. New Phytologist 167: 665–691.
    Schroeder JI, Allen GJ, Hugouvieux V, Kwak JM and Waren D (2001) Guard cell signal transduction. Annual Review of Plant Physiology and Plant Molecular Biology 52: 627–658.
    Shimazaki KI, Doi M, Assmann SM and Kinoshita T (2007) Light regulation of stomatal movement. Annual Review of Plant Biology 58: 219–247.
    book Zeiger E, Farquhar GD and Cowan IR (eds) (1987) Stomatal Function. Stanford, CA: Stanford University Press.

Related Sub-Topics:

Plant Development | Plant Responses to the Environment | Plant Evolution | Leaves
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Article Title: Stomata
 
How to Cite close
Roelfsema, M Rob G, and Hedrich, Rainer(Mar 2009) Stomata. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0002075.pub2]