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How plants utilize even the smallest amount of light effectively

20.10.2005 - (idw) Friedrich-Schiller-Universität Jena

Biologists of the Jena University involved in publication in "Nature" on two regulator enzymes of photosynthesis Jena (20.10.2005) When the sun beats down on us too much we search for a shady spot. Plants do not have this option. They are confined to their habitat, where they grew roots. Nevertheless, they are not at the mercy of their environment. During evolution, plants developed ingenious mechanisms enabling them to adjust to changing light conditions by altering their inner structures. It is well known that plants rely on light in order to survive. They take the energy neccessary to build polysaccharides out of air and water from the sun. This process, during which plants produce the oxygen vital for us humans, is called photosynthesis. It has been known for some time now, that light-harvesting proteins within a plant contribute to a plants ability to react to changes in light conditions.

A German team of scientists now identified two important enzymes, so called kinases, which are essential for short- as well as long term adjustment reactions in plants. They allow plants to utilize even the smallest amount of light effectively. The results of this research have been published on october, 20th 2005 in the renown, professional journal "Nature". Aside from scientists of the Cologne Max-Planck Institute for Plant Breeding Research, of the Ludwig-Maximilians-University of Munich, as well as of the University of Düsseldorf, plant physiologists of Jena's Friedrich Schiller University were involved in this discovery.

"Photosynthesis takes place in a highly specialized and from the rest of the cell separated mini factory, the green chloroplasts", explains co-author PD Dr. Thomas Pfannschmidt of the Jena University. "The sun's energy is, with the help of the photosystems I and II, in two steps converted into chemically usable energy." Important for that is an even excitation of both systems. The discovered kinases named STN7 and STN8 play a decisive role in this process. During fast changes of light conditions they regulate the distribution of the absorbed solar energy between the two systems by redistributing the light-harvesting proteins between them. In cases where light conditions have been different for longer periods of time, the entire photosynthetic apparatus gets remodeled. "We were able to find out, that in this case the two photosystems I and II occur in altered proportions", Pfannschmidt explains. These changes in the stoichiometry occur after 12 to 24 hours, while the short-term response happens within 5 to 10 minutes. "The point of these adaptation reactions is to most efficiently utilize the available solar energy", according to the biologist from Jena.

The light experiments administered by Pfannschmidt and his team to mutant plants showed, that those who lacked the kinase STN7 were not able to adapt to long-term changes in light conditions. It seems that the signal to built additional photosystems does not reach the central control. "The mutant plants, which don't show the long-term adaptations because they lack STN 7 are especially interesting to us, because we want to find out, exactly how the message of changed light conditions gets to the plant's DNA, where the blueprints for the photosystems I and II are stored". Obviously, STN7 is an important messenger in the signal chain, which leads to the activation of photosystem genes. "At least we now know where the photosynthesis signal originates, and that short- and long-term responses are coupled", concludes the scientist the published research results. "Now we want to try to find out how the signals are passed on. With these two kinases we have a starting point to search for further reactiion partners", Pfannschmidt sketches out the future research.

Original publication:

V. Bonardi, P. Pesaresi, T. Becker, E. Schleiff, R. Wagner, T. Pfannschmidt, P.Jahns & D. Leister: " Photosystem II core phosphorylation and photosynthetic acclimation require two different protein kinases".

Contact:
PD Dr. Thomas Pfannschmidt
Institut für Botanik und Pflanzenphysiologie der Universität Jena
Nachwuchsgruppe "Pflanzliche Anpassungen an Umweltveränderungen: Proteinanalyse mittels Massenspektrometrie"
Dornburger Straße 159, D-07743 Jena
Tel.: 0049 / 3641 / 949236
Fax: 0049 / 3641 / 949232
E-Mail: Thomas.Pfannschmidt@uni-jena.de

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