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 A Map of the Cell’s Power Station
18.08.2017 | Albert-Ludwigs-Universität Freiburg im Breisgau

nachricht On the way to developing a new active ingredient against chronic infections
21.08.2017 | Deutsches Zentrum für Infektionsforschung

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Fizzy soda water could be key to clean manufacture of flat wonder material: Graphene

Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.

As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...

Im Focus: Exotic quantum states made from light: Physicists create optical “wells” for a super-photon

Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.

Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...

Im Focus: Circular RNA linked to brain function

For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.

While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...

Im Focus: RAVAN CubeSat measures Earth's outgoing energy

An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...

Im Focus: Scientists shine new light on the “other high temperature superconductor”

A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.

Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Call for Papers – ICNFT 2018, 5th International Conference on New Forming Technology

16.08.2017 | Event News

Sustainability is the business model of tomorrow

04.08.2017 | Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

 
Latest News

On the way to developing a new active ingredient against chronic infections

21.08.2017 | Life Sciences

Smart Computers

21.08.2017 | Information Technology

A Map of the Cell’s Power Station

18.08.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>