Salaam & Wow!
This is amazing thanx for posting very important find. Did you know that the 2 proteins that absorb Red Green & Blue in our retina are the same proteins found in the bacteria found at the bottom of the ocean, I believe converting light to energy? These are important topics to think about. --DARA --- In [email protected], rahardjo mustadjab <[EMAIL PROTECTED]> wrote: > > > > January 20, 2005 news releases | receive our news > releases by email | science beat > > > Key Molecule in Plant Photo-Protection Identified > Contact: Lynn Yarris (510) 486-5375, [EMAIL PROTECTED] > > BERKELEY, CA � Another important piece to the > photosynthesis puzzle is now in place. Researchers > with the U.S. Department of Energy's Lawrence Berkeley > National Laboratory (Berkeley Lab) and the University > of California at Berkeley have identified one of the > key molecules that help protect plants from oxidation > damage as the result of absorbing too much light. > > The researchers determined that when chlorophyll > molecules in green plants take in more solar energy > than they are able to immediately use, molecules of > zeaxanthin, a member of the carotenoid family of > pigment molecules, carry away the excess energy. > > > > (teks foto) > From left, Graham Fleming, Nancy Holt and Kris Niyogi, > of Berkeley Lab's Physical Biosciences Division, have > identified a key molecule in the photo-protection > mechanism of green plants. > > This study was led by Graham Fleming, director of > Berkeley Lab's Physical Biosciences Division and a > chemistry professor with UC Berkeley, and Kris Niyogi, > who also holds joint appointments with Berkeley Lab > and UC Berkeley. Its results are reported in the > January 21, 2005 issue of the journal Science. > Co-authoring the paper with Fleming and Niyogi were > Nancy Holt, plus Donatas Zigmantas, Leonas Valkunas > and Xiao-Ping Li. > > Through photosynthesis, green plants are able to > harvest energy from sunlight and convert it to > chemical energy at an energy transfer efficiency rate > of approximately 97 percent. If scientists can create > artificial versions of photosynthesis, the dream of > solar power as a clean, efficient and sustainable > source of energy for humanity could be realized. > > A potential pitfall for any sunlight-harvesting system > is that if the system becomes overloaded with absorbed > energy, it will likely suffer some form of damage. > Plants solve this problem on a daily basis with a > photo-protective mechanism called feedback > de-excitation quenching. Excess energy, detected by > changes in pH levels (the feedback mechanism), is > safely dissipated from one molecular system to > another, where it can then be routed down relatively > harmless chemical reaction pathways. > > Said Fleming, "This defense mechanism is so sensitive > to changing light conditions, it will even respond to > the passing of clouds overhead. It is one of Nature's > supreme examples of nanoscale engineering." > > The light harvesting system of plants consists of two > protein complexes, Photosystem I and Photosystem II. > Each complex features antennae made up of chlorophyll > and carotenoid molecules that gain extra "excitation" > energy when they capture photons. This excitation > energy is funneled through a series of molecules into > a reaction center where it is converted to chemical > energy. Scientists have long suspected that the > photo-protective mechanism involved carotenoids in > Photosystem II, but, until now, the details were > unknown. > > Said Holt, "While it takes from 10 to 15 minutes for a > plant's feedback de-excitation quenching mechanism to > maximize, the individual steps in the quenching > process occur on picosecond and even femtosecond > time-scales (a femtosecond is one millionth of a > billionth of a second). To identify these steps, we > needed the ultrafast spectroscopic capabilities that > have only recently become available." > > The Berkeley researchers used femtosecond > spectroscopic techniques to follow the movement of > absorbed excitation energy in the thylakoid membranes > of spinach leaves, which are large and proficient at > quenching excess solar energy. They found that intense > exposure to light triggers the formation of zeaxanthin > molecules which are able to interact with the excited > chlorophyll molecules. During this interaction, energy > is dissipated via a charge exchange mechanism in which > the zeaxanthin gives up an electron to the > chlorophyll. The charge exchange brings the > chlorophyll's energy back down to its ground state and > turns the zeaxanthin into a radical cation which, > unlike an excited chlorophyll molecule, is a > non-oxidizing agent. > > > > > Green plants use photosynthesis to convert sunlight > to chemical energy, but too much sunlight can result > in oxidation damage. > > To confirm that zeaxanthin was indeed the key player > in the energy quenching, and not some other > intermediate, the Berkeley researchers conducted > similar tests on special mutant strains of Arabidopsis > thaliana, a weed that serves as a model organism for > plant studies. These mutant strains were genetically > engineered to either over express or not express at > all the gene, psbS, which codes for an eponymous > protein that is essential for the quenching process > (most likely by binding zeaxanthin to chlorophyll). > > "Our work with the mutant strains of Arabidopsis > thaliana clearly showed that formation of zeaxanthin > and its charge exchange with chlorophyll were > responsible for the energy quenching we measured," > said Niyogi. "We were surprised to find that the > mechanism behind this energy quenching was a charge > exchange, as earlier studies had indicated the > mechanism was an energy transfer." > > Fleming credits calculations performed on the > supercomputers at the National Energy Research > Scientific Computing Center (NERSC), under the > leadership of Martin Head-Gordon, as an important > factor in his group's determination that the mechanism > behind energy quenching was an electron charge > exchange. NERSC is a U.S. Department of Energy > national user facility hosted by Berkeley Lab. > Head-Gordon is a UC Berkeley faculty chemist with > Berkeley Lab's Chemical Sciences Division. > > "The success of this project depended on several > different areas of science, from the greenhouse to the > supercomputer," Fleming said. "It demonstrates that to > understand extremely complex chemical systems, like > photosynthesis, it is essential to combine > state-of-the-art expertise in multiple scientific > disciplines." > > There are still many pieces of the photosynthesis > puzzle that have yet to be placed for scientists to > have a clear picture of the process. Fleming likens > the on-going research effort to the popular board > game, Clue. > > "You have to figure out something like it was Colonel > Mustard in the library with the lead pipe," he says. > "When we began this project, we didn't know who did > it, how they did it, or where they did it. Now we know > who did it and how, but we don't know where. That's > next!" > > Berkeley Lab is a U.S. Department of Energy national > laboratory located in Berkeley, California. It > conducts unclassified scientific research and is > managed by the University of California. Visit our > Website at www.lbl.gov. > > Additional Information > For additional information visit the Website at > http://www.lbl.gov/pbd/photosynthesis/default.htm ------------------------ Yahoo! Groups Sponsor --------------------~--> Give underprivileged students the materials they need to learn. Bring education to life by funding a specific classroom project. http://us.click.yahoo.com/4F6XtA/_WnJAA/E2hLAA/BRUplB/TM --------------------------------------------------------------------~-> *************************************************************************** Berdikusi dg Santun & Elegan, dg Semangat Persahabatan. 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