A complex signalling web that monitors water status in the environment and initiates responses in stomatal movements


Signalling drought in guard cells.

by Luan S. (2002)

in Plant Cell and Environment 25: 229-237. – DOI: 10.1046/j.1365-3040.2002.00758.x – 



A number of environmental conditions including drought, low humidity, cold and salinity subject plants to osmotic stress. A rapid plant response to such stress conditions is stomatal closure to reduce water loss from plants. From an external stress signal to stomatal closure, many molecular components constitute a signal transduction network that couples the stimulus to the response.

Numerous studies have been directed to resolving the framework and molecular details of stress signalling pathways in plants. In guard cells, studies focus on the regulation of ion channels by abscisic acid (ABA), a chemical messenger for osmotic stress. Calcium, protein kinases and phosphatases, and membrane trafficking components have been shown to play a role in ABA signalling process in guard cells.

Studies also implicate ABA-independent regulation of ion channels by osmotic stress. In particular, a direct osmosensing pathway for ion channel regulation in guard cells has been identified. These pathways form a complex signalling web that monitors water status in the environment and initiates responses in stomatal movements.


Stomata in Rhododendron (Ericaceae)

Photo credit: Google

Rhododendron-Park Bremen, Germany

Leaf epidermal features of Rhododendron (Ericaceae) from China and their systematic significance.

by Wang Y. G., Li G. Z., Zhang W. J., You J. C., Chen J.-K. (2007)

in Acta Phytotaxon. Sin. 45: 1-20. –


Rhododendron is the largest genus within the subfamily Rhododendroideae, which has about 1000 known species in the world and more than 500 species in China. Since the genus was established by Linnaeus, its infrageneric relationships have been well studied by many taxonomists on the basis of morphological characters and molecular data.
In 1996, Chamberlain et al. proposed a new system of Rhododendron with eight subgenera, i.e., Azaleastrum, Candidastrum, Hymenanthes, Mumeazalea, Pentanthera, Rhododendron, Therorhodion, and Tsutsusi. In this paper, micromorphological characters of leaf epidermis in 4 varieties, 48 species, 6 subgenera of Rhododendron from China were examined using light microscopy (LM) and scanning electron microscopy (SEM).
Leaf epidermal features are described and micromorphological types are distinguished here according to morphological characters such as scale, gland, foliar trichome and stomatal apparatus of leaf epidermis. It is shown that the leaf epidermal cells are usually irregular or polygonal in shape. The patterns of anticlinal walls are straight, arched or undulate.
The stomatal apparatuses are anomocytic and are usually found on abaxial, not adaxial, epidermis. The results also show that:
(1) the lepidote Rhododendron (i.e., subgen. Rhododendron), which has both scales and papillae on leaf epidermis, differs distinctly from the elepidote Rhododendron;
(2) three types of leaf epidermis are identified in subgen. Hymenanthes (i.e., R. fortunei-type, R. chihsinianum-type and R. simiarum-type), whereas four in subgen. Tsutsusi (i.e., R. mariesii-type, R. simsii-type, R. mariae-type and R. flosculum-type);
(3) except for R. westlandii and R. henryi, the species of subgen. Azaleastrum show similar morphological characters, i.e., dense stomatal apparatuses surrounded by ringed or discontinuous striates;
(4) R. molle of subgen. Pentanthera differs from the species of other subgenera on morphological characters such as foliar trichomes, dense stomatal apparatuses with asymmetrical outer stomatal rims surrounded by undulate-striates, and no gland;
(5) only R. redowskianum is found with distinct T-pieces at the polar region of guard cells in Rhododendron. The results support the conclusion inferred from molecular systematic studies that subgen. Therorhodion is the basal clade of Rhododendron. Finally, the relationships between the closely related species are also discussed on the basis of leaf epidermal features.

Identification of open stomata1-interacting proteins


Identification of open stomata1-interacting proteins reveals interactions with sucrose non-fermenting1-related protein Kinases2 and with Type 2A protein phosphatases that function in abscisic acid responses.

by Waadt R., Manalansan B., Rauniyar N., Munemasa S., Booker M. A., Brandt B., Waadt C., Nusinow D. A., Kay S. A., Kunz H. H., Schumacher K., DeLong A., Yates J. R., Schroeder J. I(2015)

in Plant Physiol. 169, 760–779. doi: 10.1104/pp.15.00575 –

PubMed Abstract | CrossRef Full Text | Google Scholar



The plant hormone abscisic acid (ABA) controls growth and development and regulates plant water status through an established signaling pathway. In the presence of ABA, pyrabactin resistance/regulatory component of ABA receptor proteins inhibit type 2C protein phosphatases (PP2Cs). This, in turn, enables the activation of Sucrose Nonfermenting1-Related Protein Kinases2 (SnRK2).

Open Stomata1 (OST1)/SnRK2.6/SRK2E is a major SnRK2-type protein kinase responsible for mediating ABA responses. Arabidopsis (Arabidopsis thaliana) expressing an epitope-tagged OST1 in the recessive ost1-3 mutant background was used for the copurification and identification of OST1-interacting proteins after osmotic stress and ABA treatments.

These analyses, which were confirmed using bimolecular fluorescence complementation and coimmunoprecipitation, unexpectedly revealed homo- and heteromerization of OST1 with SnRK2.2, SnRK2.3, OST1, and SnRK2.8.

Furthermore, several OST1-complexed proteins were identified as type 2A protein phosphatase (PP2A) subunits and as proteins involved in lipid and galactolipid metabolism.

More detailed analyses suggested an interaction network between ABA-activated SnRK2-type protein kinases and several PP2A-type protein phosphatase regulatory subunits. pp2a double mutants exhibited a reduced sensitivity to ABA during seed germination and stomatal closure and an enhanced ABA sensitivity in root growth regulation.

These analyses add PP2A-type protein phosphatases as another class of protein phosphatases to the interaction network of SnRK2-type protein kinases.

The main plant hormone that regulates the development of stomata

Arabidopsis thaliana © VIB 2012

Stomata development in plants unraveled – a valuable discovery for environmental research

by VIB (Ghent, Belgium) – (2012)




Gent researchers at VIB have unraveled the action mechanism of the main plant hormone that regulates the development of stomata. This breakthrough has important implications for environmental research and for the protection of plants against disease and stress. The study has been published in the prestigious science journal Nature Cell Biology.

Plants breathe through stomata 
Plant leaves are protected from drying out by an airtight wax layer. They breathe and release water through microscopic pores called stomata. Every year 40% of atmospheric CO2 and twice the volume of water found in our atmosphere pass through these pores. This means that stomata are not only important for plant development but also for our climate!
It’s no surprise then that these pores appear to be strictly regulated by plants. Stomata react extremely fast to internal plant signals and changes in the environment. When rain is scarce, for example, the pores will close to prevent the plant from wasting water while an automatic drought protection mechanism is triggered into action. Brassinosteroids, a class of plant hormones, play an important role in determining the number of leaf stomata, but the underlying mechanism was until now not well understood.

Brassinosteroids are crucial plant hormones
Controlling multiple aspects of plant growth and development, brassinosteroids are omnipresent in the plant kingdom. The hormones have a positive effect on the quality and productivity of crops and increase their resistance to stress and disease.
Scientist Jenny Russinova and her team, who are associated with both VIB and Ghent University, study the action mechanisms of brassinosteroids. A recent breakthrough led them to conclude that the latter also affect the number of stomata. Plants without the hormone develop many fewer stomata. The opposite is also true: more brassinosteroids dramatically increase the number of pores.

Scientific breakthrough: action mechanism deciphered!
The VIB scientists are the first to unravel the action mechanism. They were able to determine how the various agents work together to form new stomata. Their experiments showed that brassinosteroids exert direct action on speechless, the transcription factor that initiates the development of stomata. Their action allows for a multitude of different interactions. This exemplifies the strictly orchestrated regulation of stomata development, which is able to react very quickly to environmental changes or internal plant signals The study has been published in the prestigious science journal Nature Cell Biology.


Stomatal frequency and size in Morus


Studies on Micromorphology and Karyotype Analysis of Three Mulberry Genotypes (Morus spp.) 

by Venkatesh K. H. (2015)

in American Journal of Phytomedicine and Clinical Therapeutics; Vol 3, No 2 (2015) –



The study of karyotype is of great value in modern taxonomy for evolving progeny of different ploidy levels of hybridization.
Stomatal frequencies are important parameters while selecting drought resistant genotypes as being correlated with drought and disease resistant.
Micro-morphology, chromosome numbers and characters of three indigenous mulberry cultivars were studied. S13 and V1 are diploid with 2n=28 and Tr-8 is triploid with 2n=42 somatic chromosomes numbers respectively. Somatic chromosome length ranges from 1.29µm to 2.59µm where as an arm ratio ranges from 0.49 to 0.97µm. Their karyotypes were commonly bi-modal, decreasing in length from the longest to the shortest chromosomes. Experimental results have confirmed that, out of three varieties studied two are diploids with 2n=28 and one variety showed 2n=42 chromosomes. Lesser frequency of stomata in triploid than diploid varieties.
Stomatal frequency and size decrease with increase in ploidy level. It can be suggested that triploid with lesser stomatal frequency are suitable for breeding triploids resistant to drought conditions.

Stomata in Corylaceae (dicots)

Photo credit: Google

Baum Hasel, Corylus colurna 3.JPG (Tree Hazelnut)

A comparative study of leaf epidermis in European Corylaceae.

SEM, LM. Corylus, Carpinus, Ostrya. Cell sizes of cells above veins, epidermal cells, stomata, frequency & types of stomata & trichomes.

by Uzunova K. (1999)

in Feddes Rep. 110. 209-218. –DOI: 10.1002/fedr.19991100307 – 

http://onlinelibrary.wiley.com/doi/10.1002/fedr.19991100307/abstract – (On our blog) – 


A study of the epidermis of European Corylaceae is presented. All three genera can be distinguished by the leaf epidermis structure. Corylus avellana L. and  C. colurna L. differ only in numerical quantitative characters such as trichome frequency and combinations of the trichomes.

Carpinus betulus L. and C. orientalis MILL. are very distinct in the structure of the stomatal apparatus, epidermal surface and appearence of anticlinal and periclinal walls. As a rule such large differences are more characteristic of the generic level. Ostrya carpinifoliaSCOP. possesses prominently dense cuticular striations on the lower epidermis and acicular trichomes on the upper epidermis.

Paracyclic, cyclocytic and laterocytic stomatal types were reported for the first time for the family. Those stomatal types corroborate the hamamelidian relationships of the family.

Despite the differences in epidermal structures e.g. a combination of various stomatal types and cuticle ornamentation the investigated species as a whole form a natural evolutionary unit.


Stomata in Phyllanthus (Euphorbiaceae)

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Phyllanthus amarus

Taxonomic Significance of Foliar Epidermis of some Phyllanthus species in South Eastern Nigeria.

by Uka C. J., Okeke C.U., Awomukwu D. A., Aziagba B., Muoka R. (2014)

1Uka, C. J., 2Okeke, C. U, 3Awomukwu, D. A., 4Aziagba, B. and 5Muoka, R.

1,2,4 Department of Botany, Nnamdi Azikiwe Univerisity, Awka, Anambra State

3Department of Biology/ Microbiology, Abia State Polytechnic, P.M.B 7166, Aba, Abia State

5Department of Botany, Federal Poltechnic, Oko, Anambra State

in IOSR Journal of Pharmacy and Biological Sciences:Vol. 9, 4, 01-06 –



Leaf epidermal studies were carried out on six species of Phyllanthus L., Family Euphorbiaceae occurring in South Eastern Nigeria. The species investigated include

P. amarus Schum and Thonn, P. urinaria Linn., P. odontadenius Mull-Arg., P. niruroides Mull-Arg., P. mullerianus (O. Ktze) Excel and P. discoideus (Baill) Mull-Arg.

The study was done in order to investigate their taxonomic relationship and to identify epidermal features that can be recognized and employed as useful taxonomic characters.

Qualitative features of the epidermal morphology showed variations in shapes of the epidermal cells and types of stomata, which varied from wavy, polygonal to sinuous and anisocystic, tetracytic to paracytic respectively in the different species.

Differences were found in the distribution of the stomata as well as the variation in the cell wall contours and thickness. Also, a quantitative trait such as the stomatal index (SI) was described in details in the present study.

A key for identification of the species is provided.