 |
|
Berkeley Researchers Identify Photosynthetic Dimmer Switch
May 09, 2008BERKELEY, CA - In a study of the molecular mechanisms by which plants protect themselves from oxidation damage should they absorb too much sunlight during photosynthesis, a team of researchers has discovered a molecular "dimmer switch" that helps control the flow of solar energy moving through the system of light harvesting proteins. This discovery holds important implications for the future design of artificial photosynthesis systems that could provide the world with a sustainable and secure source of energy.
The pigment-binding protein CP29, one of the "minor" light-harvesting proteins in green plants, has been identified as a valve that permits or blocks the critical release of excess solar energy during photosynthesis. Furthermore, it has been proposed that the opening and closing of this valve can be controlled by raising or lowering ambient pH levels.
Graham Fleming, a physical chemist who holds joint appointments with the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC) at Berkeley, was one the leaders of this study, along with Krishna Niyogi, who also holds a joint appointment with Berkeley Lab and UC Berkeley, and Roberto Bassi, of the University of Verona, Italy.
"This is really the first detailed picture ever obtained of the molecular mechanism behind the regulation of light harvesting energy," Fleming said. "We believe we will soon be in position to build a complete model of the flow of energy through the photosynthetic light harvesting system that will include how the flow is controlled. This model could then be applied to the engineering of artificial versions of photosynthesis."
The results of this study are reported in the journal Science (May 9, 2008) in a paper entitled: "Architecture of a Charge-Transfer State Regulating Light Harvesting in a Plant Antenna Protein." Co-authoring the paper with Fleming, Niyogi and Bassi were Tae Kyu Ahn, Thomas Avenson, Matteo Ballottari and Yuan-Chung Cheng.
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 the ultimate green and renewable source of electrical energy could be realized. However, a potential pitfall for any sunlight-harvesting system is that if the system becomes overloaded with absorbed solar energy, it most likely will suffer some form of damage. Plants solve this problem on a daily basis with a photo-protective mechanism called energy-quenching. Excess energy, detected by changes in pH levels, is safely dissipated from one molecular system to another, where it can then be routed down relatively harmless chemical reaction pathways.
As Fleming once explained, "This defense mechanism is so sensitive to changing light conditions, it will even respond to the passing of clouds overhead."
In 2005, Fleming and his research group identified zeaxanthin, a member of the carotenoid family of pigment molecules, as the safety outlet in the photo-protection of green plants. A plant's light harvesting system 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. Fleming and his group found that intense exposure to light triggers the formation of zeaxanthin molecules in Photosystem II. These zeaxanthin molecules interact with excited chlorophyll molecules and dissipate the excess energy via a charge-transfer mechanism - zeaxanthin gives up an electron to the chlorophyll, bringing the chlorophyll's energy back down to its ground state and turning the zeaxanthin into a radical cation which, unlike an excited chlorophyll molecule, is a non-oxidizing agent. However, until now a critical piece to the puzzle was missing - they did not know how the chlorophyll and zeaxanthin interaction was being regulated.
"If this were the murder mystery board game Clue, you could say that we had found the weapon (zeaxanthin) but didn't know how and precisely where the crime took place," Fleming said.
Fleming and his colleagues knew where to look, however. Recently they'd used near-infrared absorption spectroscopy to demonstrate that the generation of the zeaxanthin radical cation occurs exclusively in the three minor light-harvesting proteins, C29, CP26 and CP24. To determine whether one or all of the minor complexes were responsible for production of the energy-quenching cation, they expressed CP29, CP26 and CP24 in bacteria and reconstituted them in vitro with chlorophyll, zeaxanthin and other Photosystem II proteins. They then used ultrafast pump-probe spectroscopy to follow the energy trail on the femtosecond timescale (a femtosecond is one millionth of a billionth of a second) of the energy-quenching process.
"Our findings showed that energy-quenching occurs within all three minor complexes, which is consistent with the results of previous genetic and spectroscopic analyses that indicated no single antenna protein is specifically required for quenching to take place," said Fleming.
To learn more about how the energy quenching process works, Fleming and his colleagues focused their efforts on C29 because the genetics and molecular architecture of this protein have been well characterized and the supply of known mutations is ample. Their findings suggest that the change in pH as a result of excess solar energy results in CP29 undergoing a conformational change which alters the reduction potential of excitonically-coupled chlorophyll molecules. This then promotes the charge-transfer with zeaxanthin that produces radical cations. Furthermore, it appears that this conformational change is reversible, which opens the possibility of being able to "tune" the electronic coupling between the chlorophylls and thereby modulate the energy of the chlorophylls-zeaxanthin charge-transfer state. In other words, they should be able to switch the energy-quenching process on or off.
"The next step is to examine the energy quenching mechanism in the rest of the Photosystem II complex to see how it is used to regulate the flow of energy throughout the light harvesting system," said Fleming.
Support for this research came from the U.S. Department of Energy's Office of Basic Energy Sciences through its Chemical Sciences, Geosciences, and Biosciences Division.
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 more information on the research of Graham Fleming,
visit his Website at http://www.cchem.berkeley.edu/grfgrp/
* For more information on the research of Krishna Niyogi,
visit his Website at http://mollie.berkeley.edu/~niyogi/
* For more information on the research of Roberto Bassi,
visit his Website at http://www.scienze.univr.it/fol/main?ent=persona&id=82
Lawrence Berkeley National Laboratory
"This is really the first detailed picture ever obtained of the molecular mechanism behind the regulation of light harvesting energy," Fleming said. "We believe we will soon be in position to build a complete model of the flow of energy through the photosynthetic light harvesting system that will include how the flow is controlled. This model could then be applied to the engineering of artificial versions of photosynthesis."
The results of this study are reported in the journal Science (May 9, 2008) in a paper entitled: "Architecture of a Charge-Transfer State Regulating Light Harvesting in a Plant Antenna Protein." Co-authoring the paper with Fleming, Niyogi and Bassi were Tae Kyu Ahn, Thomas Avenson, Matteo Ballottari and Yuan-Chung Cheng.
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 the ultimate green and renewable source of electrical energy could be realized. However, a potential pitfall for any sunlight-harvesting system is that if the system becomes overloaded with absorbed solar energy, it most likely will suffer some form of damage. Plants solve this problem on a daily basis with a photo-protective mechanism called energy-quenching. Excess energy, detected by changes in pH levels, is safely dissipated from one molecular system to another, where it can then be routed down relatively harmless chemical reaction pathways.
As Fleming once explained, "This defense mechanism is so sensitive to changing light conditions, it will even respond to the passing of clouds overhead."
In 2005, Fleming and his research group identified zeaxanthin, a member of the carotenoid family of pigment molecules, as the safety outlet in the photo-protection of green plants. A plant's light harvesting system 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. Fleming and his group found that intense exposure to light triggers the formation of zeaxanthin molecules in Photosystem II. These zeaxanthin molecules interact with excited chlorophyll molecules and dissipate the excess energy via a charge-transfer mechanism - zeaxanthin gives up an electron to the chlorophyll, bringing the chlorophyll's energy back down to its ground state and turning the zeaxanthin into a radical cation which, unlike an excited chlorophyll molecule, is a non-oxidizing agent. However, until now a critical piece to the puzzle was missing - they did not know how the chlorophyll and zeaxanthin interaction was being regulated.
"If this were the murder mystery board game Clue, you could say that we had found the weapon (zeaxanthin) but didn't know how and precisely where the crime took place," Fleming said.
Fleming and his colleagues knew where to look, however. Recently they'd used near-infrared absorption spectroscopy to demonstrate that the generation of the zeaxanthin radical cation occurs exclusively in the three minor light-harvesting proteins, C29, CP26 and CP24. To determine whether one or all of the minor complexes were responsible for production of the energy-quenching cation, they expressed CP29, CP26 and CP24 in bacteria and reconstituted them in vitro with chlorophyll, zeaxanthin and other Photosystem II proteins. They then used ultrafast pump-probe spectroscopy to follow the energy trail on the femtosecond timescale (a femtosecond is one millionth of a billionth of a second) of the energy-quenching process.
"Our findings showed that energy-quenching occurs within all three minor complexes, which is consistent with the results of previous genetic and spectroscopic analyses that indicated no single antenna protein is specifically required for quenching to take place," said Fleming.
To learn more about how the energy quenching process works, Fleming and his colleagues focused their efforts on C29 because the genetics and molecular architecture of this protein have been well characterized and the supply of known mutations is ample. Their findings suggest that the change in pH as a result of excess solar energy results in CP29 undergoing a conformational change which alters the reduction potential of excitonically-coupled chlorophyll molecules. This then promotes the charge-transfer with zeaxanthin that produces radical cations. Furthermore, it appears that this conformational change is reversible, which opens the possibility of being able to "tune" the electronic coupling between the chlorophylls and thereby modulate the energy of the chlorophylls-zeaxanthin charge-transfer state. In other words, they should be able to switch the energy-quenching process on or off.
"The next step is to examine the energy quenching mechanism in the rest of the Photosystem II complex to see how it is used to regulate the flow of energy throughout the light harvesting system," said Fleming.
Support for this research came from the U.S. Department of Energy's Office of Basic Energy Sciences through its Chemical Sciences, Geosciences, and Biosciences Division.
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 more information on the research of Graham Fleming,
visit his Website at http://www.cchem.berkeley.edu/grfgrp/
* For more information on the research of Krishna Niyogi,
visit his Website at http://mollie.berkeley.edu/~niyogi/
* For more information on the research of Roberto Bassi,
visit his Website at http://www.scienze.univr.it/fol/main?ent=persona&id=82
Lawrence Berkeley National Laboratory
Photosynthesis Current Events and Photosynthesis News RSSChemists describe solar energy progress and challenges, including the 'artificial leaf'
Scientists are making progress toward development of an "artificial leaf" that mimics a real leaf's chemical magic with photosynthesis - but instead converts sunlight and water into a liquid fuel such as methanol for cars and trucks.
Toward home-brewed electricity with 'personalized solar energy'
New scientific discoveries are moving society toward the era of "personalized solar energy," in which the focus of electricity production shifts from huge central generating stations to individuals in their own homes and communities.
Sun or shade: Pecan leaves' photosynthetic light response evaluated
Pecan, the most valuable nut tree native to North America, is native from northern Illinois and southeastern Iowa to the Gulf Coast of the United States, where it grows abundantly along the Mississippi River, the rivers of central and eastern Oklahoma, and Texas.
Reflective film can boost profits for apple growers
In a research report published in a recent issue of HortTechnology, scientists Ignasi Iglesias and Simó Alegre examined the effects of covering orchard floors with reflective films on fruit color, fruit quality, canopy light distribution, orchard temperature, and profitability.
Iron controls patterns of nitrogen fixation in the Atlantic
Scientists including researchers from the National Oceanography Centre, Southampton and the University of Essex have discovered that interactions between iron supply, transported through the atmosphere from deserts, and large-scale oceanic circulation control the availability of a crucial nutrient, nitrogen, in the Atlantic.
Heavy metals accumulate more in some mushrooms than in others
A research team from the University of Castilla-La Mancha (UCLM) has analysed the presence of heavy metals in 12 species of mushroom collected from non-contaminated natural areas, and has found that the levels vary depending on the type of mushroom.
Arctic land and seas account for up to 25 percent of world's carbon sink
In a new study in the journal Ecological Monographs, ecologists estimate that Arctic lands and oceans are responsible for up to 25 percent of the global net sink of atmospheric carbon dioxide.
Early hominid first walked on two legs in the woods
Among the many surprises associated with the discovery of the oldest known, nearly complete skeleton of a hominid is the finding that this species took its first steps toward bipedalism not on the open, grassy savanna, as generations of scientists - going back to Charles Darwin - hypothesized, but in a wooded landscape.
Light, photosynthesis help bacteria invade fresh produce
Exposure to light and possibly photosynthesis itself could be helping disease-causing bacteria to be internalized by lettuce leaves, making them impervious to washing, according to research published in the October issue of the journal Applied and Environmental Microbiology.
'Green Clean:' Researchers Determining Natural Ways To Clean Contaminated Soil
Researchers at North Carolina State University are working to demonstrate that trees can be used to degrade or capture fuels that leak into soil and ground water. Through a process called phytoremediation - literally a "green" technology - plants and trees remove pollutants from the environment or render them harmless.
More Photosynthesis Current Events and Photosynthesis News Articles
 |
Photosynthesis (Science Concepts, Second Series) by Alvin Silverstein (Author), Virginia B. Silverstein (Author), Laura Silverstein Nunn (Author) Explains photosynthesis, the process responsible for providing the material and energy for all living things, and discusses such related issues as respiration, the carbon cycle, acid rain, and the greenhouse effect. |
 |
What Is Photosynthesis? DVD Starring: Artist Not Provided Photosynthesis is a biological process that benefits all living things. The chemical reactions that occur during the process of photosynthesis are described with the help of graphics and easy-to-follow explanations. This video makes learning about plants and how they function both fun and interesting. |
 |
Phonosynthesis by DJ Irene |
 |
Molecular Mechanisms of Photosynthesis by Robert E Blankenship (Author) Molecular Mechanisms of Photosynthesis stands as an ideal introduction to this subject. Robert Blankenship, a leading authority in photosynthesis research, offers a modern approach to photosynthesis in this accessible and well-illustrated text. The book provides a concise overview of the basic principles of energy storage and the history of the field, then progresses into more advanced topics such as electron transfer pathways, kinetics, genetic manipulations, and evolution. Throughout, Blankenship includes an interdisciplinary emphasis that makes this book appealing across fields. Leading authority in Photosynthesis and the the President of the International Society of Photosynthesis Research. First authoritative text to enter the market in 10 years. Stresses an... |
 |
Photosynthesis Also With: Josh Kalis (Primary Contributor), Rob Dyrdek (Primary Contributor), Jason Dill (Primary Contributor), Danny Way (Primary Contributor), Anthony van Engelen (Primary Contributor), Anthony Pappalardo (Primary Contributor), Pat Corcoran (Primary Contributor), Kerry Getz (Primary Contributor), Fred Gall (Primary Contributor), Tim O'Connor (Primary Contributor) Skater list Anthony Pappalardo Anthony Van Engelen Danny Garcia Fred Gall Jason Dill Josh Kalis Kerry Getz Mark Appleyard Pat Corcoran Rob Dyrdek Tim O'Connor |
 |
Photosynthesis: Changing Sunlight into Food (Nature's Changes) by Bobbie Kalman (Author) This title contains a book & CD. Photosynthesis is the basis for all life on Earth! This exciting and sensitive book looks at how plants use a gas that is poisonous to people and animals to create food and oxygen for all creatures with the help of the Sun. The CD's approximate running time is 30 minutes. |
 |
Photosynthesis Rhyme, Results Rhythm (Primary Contributor) |
 |
Vintage Photosynthesis Biochemistry Science Film DVD: Classic Water, Oxygen Cycle, Plant Life, Sunlight & Carbon Video Photosynthesis is pretty much the most important biological process that takes place on this planet, because almost everything living depends on photosynthesis to survive. Gift of Green is a vintage science film dealing with the process of photosynthesis. Now, this digitized film is available on DVD for the first time ever! Table Of Contents: (1) Gift of Green (1946) - This is a vintage science class film featuring animation that shows the process of photosynthesis. Highly recommended and well-made for its era! - 16 Minutes |
 |
Photosynthesis by Dr David Lawlor (Author) Now in its third edition, this book describes photosynthesis by considering the partial processes involved throughout the various level of plant (cell, organelle and molecule), and their contributions to the complete process. It also considers the molecular and biochemical events which take place in the photosynthetic system. Finally, it explains how these determine the physiological characteristics of plant productivity. |
 |
Photosynthesis by Plants "Plants play a mystical brand of psychedelic folk whose solemn, droning beauty and stately pace recall Six Organs of Admittance and Pearls Before Swine at their most pastoral and intense."- Dave Segal, The Stranger Formed by wedded musical partners Joshua & Molly Blanchard to explore delicate acid-folk terrain, Plants has evoloved well beyond its sparse, mystical roots to sail along a rich and diverse confluence of mind-enhancing streams. 2006 bore witness to a trilogy of recordings, from the quivering folk of debut The Mind is a Bird in the Hand to music captured in yurts and bunkers along the Oregon coast(Totem CD-R) and the pillow-prog odyssey Double Infinity. Photosynthesis, the group's fourth album, is aptly named, illustrating the subtle skill with which Plants ... |
| © 2009 BrightSurf.com |