Cuticular waxes and stomatal development.

 

A role for the cuticular waxes in the environmental control of stomatal development.

by Holroyd G. H.,

Hetherington A. M.,

Gray J. E.

(2002)

in New Phytologist 153: 433–439. – DOI: 10.1046/j.0028-646X.2001.NPH326.doc.x

CrossRef |CAS |

http://onlinelibrary.wiley.com/doi/10.1046/j.0028-646X.2001.NPH326.doc.x/abstract

Summary

The mechanism of guard cell development is currently attracting much interest. The recent use of Arabidopsis mutant plants has shed new light on the pathways that regulate the development and patterning of specialized cells such as guard cells, trichomes and roots hairs within the plant epidermis.

Here, we review this literature focusing on the insights provided into guard cell development. We also discuss our current knowledge of how environmental variables may impact on guard cell development and, in particular, consider whether the composition of the epidermal waxes may be involved in this process.

 

Stomata and response of grafted plants to soil drying.

 

Stomatal control in tomato with ABA-deficient roots: response of grafted plants to soil drying.

by Holbrook N. M.,

Shashidhar V. R., James R. A.,

Munns R.

(2002)

in J Exp Bot. 2002 Jun;53(373):1503-14. – doi:10.1093/jexbot/53.373.1503

CAS, PubMed, Article

http://www.ncbi.nlm.nih.gov/pubmed/12021298?dopt=Abstract&holding=npg

http://jxb.oxfordjournals.org/content/53/373/1503

Abstract

The hypothesis that ABA produced by roots in drying soil is responsible for stomatal closure was tested with grafted plants constructed from the ABA‐deficient tomato mutants, sitiens and flacca and their near‐isogenic wild‐type parent.

Three types of experiments were conducted. In the first type, reciprocal grafts were made between the wild type and sitiens orflacca. Stomatal conductance accorded with the genotype of the shoot, not the root. Stomates closed in all of the grafted plants in response to soil drying, regardless of the root genotype, i.e. regardless of the ability of the roots to produce ABA.

In the second type of experiment, wild‐type shoots were grafted onto a split‐root system consisting of one wild‐type root grafted to one mutant (flacca or sitiens) root. Water was withheld from one root system, while the other was watered well so that the shoots did not experience any decline in water potential or loss of turgor. Stomates closed to a similar extent when water was withheld from the mutant roots or the wild‐type roots.

In the third type of experiment, grafted plants with wild‐type shoots and either wild‐type or sitiens roots were established in pots that could be placed inside a pressure chamber, and the pressure increased as the soil dried so that the shoots remained fully turgid throughout. Stomates closed as the soil dried, regardless of whether the roots were wild type or sitiens.

These experiments demonstrate that stomatal closure in response to soil drying can occur in the absence of leaf water deficit, and does not require ABA production by roots. A chemical signal from roots leading to a change in apoplastic ABA levels in leaves may be responsible for the stomatal closure.

ICE1/SCRM2 and stomatal development

 

They All Scream for ICE1/SCRM2: Core Regulatory Units in Stomatal Development

by Hofmann N. R.

(2008)

in The Plant Cell, July 2008 vol. 20 no. 7 1732 – 

http://www.plantcell.org/content/20/7/1732.full 

• American Society of Plant Biologists

The developmental program of stomata includes a series of both symmetrical and asymmetrical divisions and provides an excellent, technically accessible model for the study of patterning, cell fate specification, and regulation of cell division (reviewed in Bergmann and Sack, 2007). Three basic-helix-loop-helix (bHLH) transcription factors, SPEECHLESS (SPCH), MUTE, and FAMA, have been shown to mediate this process at different steps. Kanaoka et al. (pages 1775–1785) further elucidate the regulation of stomatal development by characterizing an Arabidopsismutant, scrm-D, that forms ectopic stomata.

The homozygous scrm-D mutant has an epidermis made entirely of stomata (see figure ). Because the scrm-D phenotype is identical to that caused by ectopic expression of MUTE, the authors examined the genetic interactions between scrm-D and the known regulators of stomatal development. They found that SCRM likely acts upstream of MUTE and FAMA and that there are dose-dependent effects of SPCH on SCRM, suggesting that they might interact at the molecular level.

The scrm-D mutation causes ectopic stomata. In the wild-type epidermis (left), stomata are separated from each other by at least one pavement cell. Thescrm-D homozygous mutant epidermis (right) is made up entirely of stomata. Bar = 20 μm.

Map-based cloning revealed that SCRM is INDUCER of CBF EXPRESSION1 (ICE1), a bHLH transcription factor that positively regulates the cold-induced transcriptome and freezing tolerance. GUS and GFP fusions showed that ICE1 is nuclear localized and is broadly expressed in stomatal lineage cells. In addition, the same R-to-H substitution found in scrm-D is able to cause ectopic stomata when introduced into SCRM2, an ICE1 paralog identified in this study. An examination of the phenotypes of ice1 and scrm2 null mutants indicated that the two proteins are redundant and act to promote sequential steps of stomatal cell development program: entry, proliferation, and terminal differentiation.

Since bHLH transcription factors form dimers, the authors tested whether these proteins heterodimerize and found that the ICE1 proteins each interact with MUTE, FAMA, and SPCH. These data suggest that ICE1 and SCRM2, which are both expressed throughout stomatal development, form dimers with MUTE, FAMA, and SPCH, which are expressed in specific cells, to regulate the formation of stomata in the epidermis.

This work demonstrates that the regulation of cell division and pattern formation in plants can be strikingly similar to that in other systems. For instance, the broadly expressed myocyte enhancer binding factor 2 family MADS box proteins interact with more restricted bHLH proteins to regulate muscle formation (reviewed in Molkentin and Olson, 1996). In addition, it has long been known that environmental factors contribute to stomatal patterning (reviewed in Casson and Gray, 2008). The finding that ICE1, a regulator of freezing tolerance, is also involved in stomatal development might provide a needed entry point into understanding the link between environmental responses and the formation of stomata.

Nancy R. Hofmann

The multifaceted functions of NaMPK4 in

 

Silencing MPK4 in Nicotiana attenuata enhances photosynthesis and seed production but compromises abscisic acid-induced stomatal closure and guard cell-mediated resistance to Pseudomonas syringae pv tomato DC3000.

by Hettenhausen C.,

Baldwin I. T.,

Wu J.

(2012)

in Plant Physiol. 158, 759–776. doi: 10.1104/pp.111.190074 –

PubMed Abstract | CrossRef Full Text | Google Scholar

http://www.plantphysiol.org/content/158/2/759

Abstract

Mitogen-activated protein kinases (MAPKs) play pivotal roles in development and environmental interactions in eukaryotes.

Here, we studied the function of a MAPK, NaMPK4, in the wild tobacco species Nicotiana attenuata. The NaMPK4-silenced N. attenuata (irNaMPK4) attained somewhat smaller stature, delayed senescence, and greatly enhanced stomatal conductance and photosynthetic rate, especially during late developmental stages. All these changes were associated with highly increased seed production.

Using leaf epidermal peels, we demonstrate that guard cell closure in irNaMPK4 was strongly impaired in response to abscisic acid and hydrogen peroxide, and consistently, irNaMPK4 plants transpired more water and wilted sooner than did wild-type plants when they were deprived of water.

We show that NaMPK4 plays an important role in the guard cell-mediated defense against a surface-deposited bacterial pathogen, Pseudomonas syringae pv tomato (Pst) DC3000; in contrast, when bacteria directly entered leaves by pressure infiltration, NaMPK4 was found to be less important in the resistance to apoplast-located Pst DC3000.

Moreover, we show that salicylic acid was not involved in the defense against PstDC3000 in wild-type and irNaMPK4 plants once it had entered leaf tissue.

Finally, we provide evidence that NaMPK4 functions differently from AtMPK4 and AtMPK11 in Arabidopsis (Arabidopsis thaliana), despite their sequence similarities, suggesting a complex functional divergence of MAPKs in different plant lineages.

This work highlights the multifaceted functions of NaMPK4 in guard cells and underscores its role in mediating various ecologically important traits.

Ca2+ signals and stomata

 

The generation of Ca²⁺ signals in plants. 

Hetherington  A. M., Brownlee C. (2004)

in Annu. Rev. Plant Biol. 55, 401–427. –

CrossRef | PubMed | CAS |

http://www.ncbi.nlm.nih.gov/pubmed/15377226

Abstract

The calcium ion is firmly established as a ubiquitous intracellular second messenger in plants. At their simplest, Ca(2+)-based signaling systems are composed of a receptor, a system for generating the increase in [Ca(2+)]cyt, downstream components that are capable of reacting to the increase in [Ca(2+)]cyt, and other cellular systems responsible for returning [Ca(2+)]cyt to its prestimulus level.

Here we review the various mechanisms responsible for generating the stimulus-induced increases in [Ca(2+)]cyt known as Ca(2+) signals. We focus particularly on the mechanisms responsible for generating [Ca(2+)]cyt oscillations and transients and use Nod Factor signaling in legume root hairs and stimulus-response coupling in guard cells to assess the physiological significance of these classes of Ca(2+) signals.

ABA signaling in stomata

 

Guard cell signaling.

Hetherington A. M. (2001) 

in Cell 107: 711–714 – 

CAS, ISI, PubMed, Article, CrossRef, Medline, Web of Science, Google Scholar

http://www.ncbi.nlm.nih.gov/pubmed/11747807?dopt=Abstract&holding=npg

Abstract

The plant hormone abscisic acid (ABA) regulates the aperture of the stomatal pore. The recent identification of new intermediates involved in ABA signaling suggests that this complex pathway is organized as a module-based network.

Photosynthesis and stomatal conductance

 

Optimal stomatal conductance in relation to photosynthesis in climatically contrasting Eucalyptus species under drought.

by Héroult A.,

Lin Y.-S.,

Bourne A.,

Medlyn B. E.,

Ellsworth D. S.

 (2013)

in Plant Cell Environ. 36, 262–274 (2013). – doi: 10.1111/j.1365-3040.2012.02570.x.

CAS, ISI, PubMed, Article

http://www.ncbi.nlm.nih.gov/pubmed/22762345?dopt=Abstract&holding=npg

Abstract

Models of stomatal conductance (g(s)) are based on coupling between g(s) and CO(2) assimilation (A(net)), and it is often assumed that the slope of this relationship (‘g(1) ‘) is constant across species. However, if different plant species have adapted to different access costs of water, then there will be differences in g(1) among species.

We hypothesized that g(1) should vary among species adapted to different climates, and tested the theory and its linkage to plant hydraulics using four Eucalyptus species from different climatic origins in a common garden.

Optimal stomatal theory predicts that species from sub-humid zones have a lower marginal water cost of C gain, hence lower g(1) than humid-zone species. In agreement with the theory that g(1) is related to tissue carbon costs for water supply, we found a relationship between wood density and g(1) across Eucalyptus species of contrasting climatic origins.

There were significant reductions in the parameter g(1) during drought in humid but not sub-humid species, with the latter group maintaining g(1) in drought. There are strong differences in stomatal behaviour among related tree species in agreement with optimal stomatal theory, and these differences are consistent with the economics involved in water uptake and transport for carbon gain.

Stomatal density, drought tolerance and nutrient uptake

 

Manipulating stomatal density enhances drought tolerance without deleterious effect on nutrient uptake.

by Hepworth C.,

Doheny-Adams T.,

Hunt L.,

Cameron D.D.,

 Gray J.E.

(2015)

in New Phytologist, 208 (2). pp. 336-341. ISSN 0028-646X – DOI: 10.1111/nph.13598

http://eprints.whiterose.ac.uk/90224/ – http://dx.doi.org/10.1111/nph.13598

Summary

• Manipulation of stomatal density was investigated as a potential tool for enhancing drought tolerance or nutrient uptake.
• Drought tolerance and soil water retention were assessed using Arabidopsis epidermal patterning factor mutants manipulated to have increased or decreased stomatal density. Root nutrient uptake via mass flow was monitored under differing plant watering regimes using nitrogen-15 (¹⁵N) isotope and mass spectrometry.
• Plants with less than half of their normal complement of stomata, and correspondingly reduced levels of transpiration, conserve soil moisture and are highly drought tolerant but show little or no reduction in shoot nitrogen concentrations especially when water availability is restricted. By contrast, plants with over twice the normal density of stomata have a greater capacity for nitrogen uptake, except when water availability is restricted.
• We demonstrate the possibility of producing plants with reduced transpiration which have increased drought tolerance, with little or no loss of nutrient uptake. We demonstrate that increasing transpiration can enhance nutrient uptake when water is plentiful.

Physiological aspects of stomatal function

 

Changes in apoplastic pH and membrane potential in leaves in relation to stomatal responses to CO₂, malate, abscisic acid or interruption of water supply.

by Hedrich R., Neimanis S., Savchenko G., Felle H. H., Kaiser W. M., Heber U. (2001)

in Planta 213: 594–601 –

[PubMed]

Abstract

Low CO2 concentrations open CO2-sensitive stomata whereas elevated CO2 levels close them. This CO2 response is maintained in the dark. To elucidate mechanisms underlying the dark CO2 response we introduced pH- and potential-sensitive dyes into the apoplast of leaves. After mounting excised leaves in a gas-exchange chamber, changes in extracellular proton concentration and transmembrane potential differences as well as transpiration and respiration were simultaneously monitored.

Upon an increase in CO2 concentration transient changes in apoplastic pH (occasionally brief acidification, but always followed by alkalinization) and in membrane potential (brief hyperpolarization followed by depolarization) accompanied stomatal closure.

Alkalinization and depolarization were also observed when leaves were challenged with abscisic acid or when water flow was interrupted. During stomatal opening in response to CO2-free air the apoplastic pH increased while the membrane potential initially depolarized before it transiently hyperpolarized.

To examine whether changes in apoplastic malate concentrations represent a closing signal for stomata, malate was fed into the transpiration stream. Although malate caused apoplastic alkalinization and membrane depolarization reminiscent of the effects observed with CO2 and abscisic acid, this dicarboxylate closed the stomata only partially and less effectively than CO2.

Apoplastic alkalinization was also observed and stomata closed partially when KCl was fed to the leaves. Respiration increased on feeding of malate or KCl, or while abscisic acid closed the stomata.

From these results we conclude that CO2 signals modulate the activity of plasma-membrane ion channels and of plasmalemma H+-ATPases during changes in stomatal aperture. Responses to potassium malate and KCl are not restricted to guard cells and neighbouring cells.

 

Malate-sensitive anion channels, CO2 and stomata

 

Malate-sensitive anion channels enable guard cells to sense changes in the ambient CO2 concentration.

by Hedrich R., Marten I., Lohse G., Dietrich P., Winter H., Lohaus G., Heldt H.-W. (1994)

in Plant J. 6:741–748. – DOI: 10.1046/j.1365-313X.1994.6050741.x

CrossRefWeb of ScienceGoogle Scholar 

Summary

Malate is a characteristic metabolite in the photosynthesis of C4 and CAM plants. Furthermore, changes in the intracellular concentration of this organic acid provide part of the osmotic motor for guard cells. Since alterations in the malate concentration influence the photosynthetic capacity on one side and stomatal action on the other, it was studied whether the extracellular malate level represents an indicator of changes in the ambient CO₂ concentration and a key regulator of ion transport in guard cells.

Here it is demonstrated that alterations in the ambient CO₂ level modify the extracellular malate concentration of Vicia faba leaves. Elevated external malate caused stomatal closure in a concentration-dependent manner (K_m^mal = 0.3 mM).

Slight variations in the external malate concentration strongly regulate the voltage-dependent properties of GCAC1, an anion-release channel in the plasma membrane of guard cells. Superfusion of guard cell protoplasts with malate levels in the physiological range (K_m^mal = 0.4 mM) caused the voltage gate to shift towards the resting potential of the cell-activating GCAC1.

Single-channel conductance was dependent on the extracellular chloride concentration (K_m^Cl = 3 mM). In the absence of extracellular chloride the plasma membrane lacked anion conductance until the addition of malate induced channel opening.

Isophthalate was a powerful agonist in both malate-induced processes, channel regulation and stomatal closure, indicating that modulation of GCAC1 is a key step in stomatal action.

It was thus concluded that feedback regulation of volume and turgor with respect to the ambient CO₂ concentration via malate-sensitive anion channels may provide a CO₂ sensor to guard cells.