Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Seeing the light in the egg of a clawed frog

13.04.2010
When plants protect themselves against drying out, processes take place in which calcium plays an important role, just as it does in muscle contraction in humans. Now for the first time, Dietmar Geiger and Rainer Hedrich from the Department of Molecular Plant Physiology and Biophysics at the University of Würzburg have shed light on exactly what happens.

Plants produce sugar during photosynthesis. Water is released into the environment in the form of water vapor. This is the responsibility of tiny "valves" on the surface of the leaf, which consist of guard cells arranged in pairs. Depending on whether these guard cells are bulging or comparatively empty, they change their shape - in the same way as a swim ring, which is circular when inflated but can be folded tightly when all the air is released from it.


Plants can absorb carbon dioxide and release water vapor through microscopically small, controllable pores in their outer skin. The pores consist of two guard cells: when these expand, the pore opens. Photo: Department of Molecular Plant Physiology and Biophysics, University of Würzburgt

Guard cells regulate the water exchange

In plant terms, this means as follows: two bulging guard cells form a circle, enabling the release of water vapor into the environment. If they go limp, the valve closes, the plant retains the water internally, and in so doing protects itself against drying out. How this process works at molecular level has been examined by Dr. Dietmar Geiger. Geiger works as an assistant to Professor Rainer Hedrich in the Department of Molecular Plant Physiology and Biophysics.

The findings of his work are reported in the current issue of the journal Proceedings of the National Academy of Sciences (PNAS, USA).

"During times of drought, plants create what is known as a drought stress hormone, which causes the pairs of guard cells to go limp through a chain of reactions in which calcium is also involved," explains Dietmar Geiger. The "valve" closes, thereby reducing the release of water from the leaf. As the biophysicists discovered in earlier experiments, this process involves certain ion channels and enzymes that fine-tune the process. The scientists were able to clarify which ones exactly using a clever technique that Rainer Hedrich established a good ten years ago that allows ion channels to be examined outside plant cells. The key components are: eggs from a clawed frog and a yellow fluorescent protein.

Complicated search for the enzyme responsible

"The earlier work by Dietmar Geiger, which was also published in PNAS, led us to assume that a very specific anion channel is involved in this process," explains Rainer Hedrich. What was, however, a mystery was which enzyme is responsible for opening this channel to calcium ions. There were, after all, 34 enzymes to choose from.

It was a molecular biology trick that helped them see the light, quite literally: "We coupled the gene for the guard cell anion channel to one half of the gene for the yellow fluorescent protein. We then bonded the other half to each of the 34 possible enzyme genes in turn," explains Dietmar Geiger.

Traces of light in the egg of a clawed frog

The idea behind this: in this scenario, the yellow fluorescent protein will only illuminate when the proteins of the enzyme and of the anion channel that have been fused to the two halves are moved to within close proximity to one another. And the eggs of the clawed frog came into play because, firstly, they are sufficiently transparent and, secondly, they work perfectly as a "test tube for loading with foreign genes and translating into active proteins," says Rainer Hedrich.

The two scientists did indeed succeed in identifying the corresponding calcium-dependent enzyme, a so-called kinase, using this elegant, experimental approach, with the ion channel as bait. The Würzburg "channel workers" then applied the same approach to determine the enzyme that disables the channel again - a protein phosphatase.

Support from Munich

The following questions remained: how do these two switch elements sense the drought stress hormone, and what sensor regulates the activity of the kinase/phosphatase pair? To find this out, the Würzburg researchers collaborated with Professor Erwin Grill's team from the Technical University Munich. The people from Munich had identified a protein that deactivates the phosphatase when it has bonded with the water stress hormone.

This knowledge gave them the final link in the signal chain: "In the presence of the stress hormone, a receptor is stimulated that inhibits the phosphatase. The kinase transfers energy-rich phosphate to the anion channel, thereby activating it. The release of anions triggers a flow of potassium and water, the guard cells release their pressure, and the plant survives the drought with its stomata tightly closed", explains Dietmar Geiger.

However, not every question has been answered. There is just "one small, but not insignificant detail" remaining, says Rainer Hedrich: "How does the calcium ion get into the cell?" But for this too the Würzburg plant physiologists have already come up with an idea.

The researchers

Dr. Dietmar Geiger received his doctorate at the Department of Molecular Plant Physiology and Biophysics. He then became a post-doctoral student at the Max Planck Institute of Biophysics in Frankfurt. As an assistant to Professor Rainer Hedrich, he applies molecular and biophysical methods in order to understand the structures of ion channels and metabolite carriers that account for the special function of membrane proteins.

Professor Rainer Hedrich was a pioneer in the discovery and deciphering of the special function of ion channels in plants. So far, he has deciphered all the major ion channels of the guard cell - starting with his discovery of the first ion channel in plants, the potassium channel of the guard cell, back in 1984 while working toward his doctorate.

"Guard cell anion channel SLAC1 is regulated by CDPK protein kinases with distinct Ca2+ affinities"; Dietmar Geiger, Sönke Scherzer, Patrick Mumm, Irene Marten, Peter Ache, Susanne Matschi, Anja Liese, Christian Wellmann, Khaled A.S. AL-Rasheid, Erwin Grill, Tina Romeis and Rainer Hedrich. Proc Natl Acad Sci USA. doi/10.1073/pnas.0912030107

Contact:
Prof. Dr. Rainer Hedrich, T: +49 (0)931 31-86100,
e-mail: hedrich@botanik.uni-wuerzburg.de
Dr. Dietmar Geiger, T: +49 (0)931 31-86105,
e-mail: geiger@botanik.uni-wuerzburg.de

Gunnar Bartsch | Uni Würzburg
Further information:
http://www.botanik.uni-wuerzburg.de

More articles from Life Sciences:

nachricht Multi-institutional collaboration uncovers how molecular machines assemble
02.12.2016 | Salk Institute

nachricht Fertilized egg cells trigger and monitor loss of sperm’s epigenetic memory
02.12.2016 | IMBA - Institut für Molekulare Biotechnologie der Österreichischen Akademie der Wissenschaften GmbH

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

Im Focus: Molecules change shape when wet

Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water

In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...

Im Focus: Fraunhofer ISE Develops Highly Compact, High Frequency DC/DC Converter for Aviation

The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.

Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

UTSA study describes new minimally invasive device to treat cancer and other illnesses

02.12.2016 | Medical Engineering

Plasma-zapping process could yield trans fat-free soybean oil product

02.12.2016 | Agricultural and Forestry Science

What do Netflix, Google and planetary systems have in common?

02.12.2016 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>