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 The birth of a new protein
20.10.2017 | University of Arizona

nachricht Building New Moss Factories
20.10.2017 | Albert-Ludwigs-Universität Freiburg im Breisgau

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Neutron star merger directly observed for the first time

University of Maryland researchers contribute to historic detection of gravitational waves and light created by event

On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...

Im Focus: Breaking: the first light from two neutron stars merging

Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.

Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....

Im Focus: Smart sensors for efficient processes

Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).

When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...

Im Focus: Cold molecules on collision course

Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.

How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...

Im Focus: Shrinking the proton again!

Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.

It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ASEAN Member States discuss the future role of renewable energy

17.10.2017 | Event News

World Health Summit 2017: International experts set the course for the future of Global Health

10.10.2017 | Event News

Climate Engineering Conference 2017 Opens in Berlin

10.10.2017 | Event News

 
Latest News

Terahertz spectroscopy goes nano

20.10.2017 | Information Technology

Strange but true: Turning a material upside down can sometimes make it softer

20.10.2017 | Materials Sciences

NRL clarifies valley polarization for electronic and optoelectronic technologies

20.10.2017 | Interdisciplinary Research

VideoLinks
B2B-VideoLinks
More VideoLinks >>>