Stomatal movements and the guard cell chloroplast


The guard cell chloroplast: a perspective for the 21st century.

by Zeiger E., Talbott L. D., Frechilla S., Srivastava A., Zhu J. (2002)

Department of Organismic Biology, Ecology and Evolution, University of California, Los Angeles, 900 Veteran Ave., Los Angeles, CA 90024-1786, USA;

Eduardo Zeiger,

Lawrence D. Talbott,

Silvia Frechilla,

Alaka Srivastava,

Jianxin Zhu

in New Phytologist 153: 415424. – DOI: 10.1046/j.0028-646X.2001.NPH328.doc.x

CrossRef |CAS | –


The guard cell chloroplast is the site of perception of blue light and of photosynthetically active radiation, and of at least one of the mechanisms sensing CO2 in the guard cell. The guard cell chloroplast has been the focus of intense controversy over its capacity for light sensing and photosynthetic carbon fixation, and the osmoregulatory mechanisms mediating stomatal movements.

It is argued here that a primary reason behind these long-lived controversies is the remarkable plasticity of the guard cell, which has resulted in responses being generalized as basic properties when opposite responses appear to be the norm under different environmental or experimental conditions.

Examples of guard cell plasticity are described, including variation of chlorophyll fluorescence transients over a daily course, acclimation of the guard cell responses to blue light and CO2, the shift from potassium to sucrose in daily courses of osmoregulation and the transduction of red light into different osmoregulatory pathways.

Recent findings on the properties of the guard cell chloroplast are also presented, including the role of the chloroplastic carotenoid, zeaxanthin, in blue light photoreception, the blue-green reversibility of stomatal movements, and the involvement of phytochrome in the stomatal response to light in the orchid, Paphiopedilum.

Vacuole fluorescence in onion stomata


Blue light-induced, intrinsic vacuole fluorescence in onion guard cells.

by Zeiger E., Hepler P. K. (1979)

Eduardo Zeiger

P. K. Hepler

in  J. Cell Sci. 37, 1–10 –

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Guard cells of onion irradiated with broad-band blue light display a green intrinsic fluorescence. The fluorescence has been found in eleven species of Allium, but it has not been observed in any other monocot or dicot examined.

The fluorescence occurs only in guard cells and is absent in neighbouring epidermal cells.

During development it is first apparent in guard mother cells soon after the asymmetric division. Microscopic observation reveals that the fluorescence is associated with the vacuole and examination of vacuoles isolated from guard cell protoplasts suggests that it may be localized on the tonoplast.

Microspectrophotometric analysis of single cells reveals an emission peak at around 520 nm.

Our results are consistent with the view that this blue light receptor is a flavin or flavoprotein and that it might be related to the blue light-enhanced stomatal opening observed in onion.

The direct interaction between SRK2E/OST1 and ABI1 through Domain II plays a critical role in the control of stomatal closure


The regulatory domain of SRK2E/OST1/SnRK2.6 interacts with ABI1 and integrates abscisic acid (ABA) and osmotic stress signals controlling stomatal closure in Arabidopsis.

by Yoshida R., Umezawa T., Mizoguchi T., Takahashi S., Takahashi F., Shinozaki K. (2006)

  1. Riichiro Yoshida§,
  2. Taishi Umezawa,
  3. Tsuyoshi Mizoguchi,
  4. Seiji Takahashi,1,
  5. Fuminori Takahashi and
  6. Kazuo Shinozaki§,2

Author Affiliations

  1. Laboratory of Plant Molecular Biology, RIKEN Tsukuba Institute, 3-1-1, Koyadai, Tsukuba, Ibaraki 305-0074, Japan,
  2. §Plant Mutation Exploration Team, Plant Functional Genomics Research Group, RIKEN Genomic Sciences Center, 1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama 230-0045, Japan,
  3. Institute of Biological Sciences, Tsukuba University, Tennodai, Tsukuba, Ibaraki, 305-8572, Japan, and
  4. Gene Discovery Research Group, RIKEN Plant Science Center, 1-7-2 Suehiro-cho, Tsurumi-ku, Yokohama 230-0045, Japan

in Journal of Biological Chemistry 2006;281:5310-5318. –doi:10.1074/jbc.M509820200pmid:16365038  –



ABI1 and ABI2 encode PP2C-type protein phosphatases and are thought to negatively regulate many aspects of abscisic acid (ABA) signaling, including stomatal closure in Arabidopsis.

In contrast, SRK2E/OST1/SnRK2.6 encodes an Arabidopsis SnRK2 protein kinase and acts as a positive regulator in the ABA-induced stomatal closure. SRK2E/OST1 is activated by osmotic stress as well as by ABA, but the independence of the two activation processes has not yet been determined.

Additionally, interaction between SRK2E/OST1 and PP2C-type phosphatases (ABI1 and ABI2) is not understood.

In the present study, we demonstrated that the abi1-1 mutation, but not the abi2-1mutation, strongly inhibited ABA-dependent SRK2E/OST1 activation. In contrast, osmotic stress activated SRK2E/OST1 even in abi1-1 and aba2-1 plants.

The C-terminal regulatory domain of SRK2E/OST1 was required for its activation by both ABA and osmotic stress in Arabidopsis.

The C-terminal domain was functionally divided into Domains I and II. Domain II was required only for the ABA-dependent activation of SRK2E/OST1, whereas Domain I was responsible for the ABA-independent activation.

Full-length SRK2E/OST1 completely complemented the wilty phenotype of the srk2emutant, but SRK2E/OST1 lacking Domain II did not. Domain II interacted with the ABI1 protein in a yeast two-hybrid assay.

Our results suggested that the direct interaction between SRK2E/OST1 and ABI1 through Domain II plays a critical role in the control of stomatal closure.