NEWS FROM
PHYSIOLOGIA PLANTARUM
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Published monthly on behalf of SPPS by Wiley-Blackwell.
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Climate change causes greenhouse gas emission by plants
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Global warming seems to be self-sustaining by making plants emit the potent greenhouse gas, methane (CH4), while simultaneously reducing their assimilation of CO2. This conclusion was obtained by Mirwais M. Qaderi and David M. Reid from University of Calgary, Canada, who tested methane emission and several growth parameters from six crop species grown under various environmental conditions. An increase in temperature from 24/20 °C (day/night) to 30/26 °C led to a 15% increase in methane emission, while the effect of water stress, which will accompany global warming in many regions, increased emission of the greenhouse gas by 22%. The figures are average measurements from faba bean, sunflower, pea, canola, barley and wheat. Under ambient conditions the six crops emitted between 85 (barley) and 170 (pea) ng methane per g dry weight per hour. At the same time, the higher temperature caused CO2 assimilation to decrease 27%, while water stress reduced CO2 assimilation by 31%. The researchers will now investigate how elevated CO2 levels affect methane emission in order to get a better picture of how global warming can turn plants into greenhouse gas contributors.
Read full article free: Qaderi & Reid (October 2009) Physiologia Plantarum 137: 139-147
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NEWS IN BRIEF
FROM OTHER JOURNALS
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Amber Predates Conifers
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Source: Bray & Anderson (2 October 2009) Science 326: 132-134
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Shedding light on protein-protein interactions
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Source: Yazawa et al (4 October 2009) Nature Biotechnology doi:10.1038/nbt.1569
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Scandinavian research institute:
Department of Photochemistry and Molecular Science, Uppsala University, Sweden
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Mimicking and manipulation of natural photosynthesis can be a new source of energy. From www.fotomol.uu.se
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Photosynthesis and other photochemical reactions are key to most activities at the Department of Photochemistry and Molecular Science at Uppsala University in Sweden. Artificial photosynthesis is the common theme that connects the approximately 50 scientists - 15 senior scientists, 10 postdocs and 20 PhD students - who are engaged in a number of highly interdisciplinary project groups looking at the chemical processes that will ultimately be required to harvest solar energy in a form that can be readily used by mankind.
The overall objective is to produce molecular hydrogen and to this end two different approaches are taken. One is to utilize the cyanobacteria Nostoc punctiforme, that are naturally able to synthesize hydrogen under nitrogen starving conditions, and grow genetically manipulated and more efficient versions of this microorganism in bioreactors. The other approach is to mimic the biological processes and utilize them in light-driven artificial systems where synthetic catalysts will produce hydrogen.
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The heterocyst, a specialized bacterial cell, produces hydrogen as a waste product. From www.fotomol.uu.se
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Like green algae and other cyanobacteria, Nostoc punctiforme is able to produce free hydrogen, H2, from solar energy and water. This is achieved through a proces called nitrogen fixation, where atmospheric nitrogen is reduced by H+ to ammonia, NH4+, under the formation of H2 as a natural by-product. Under normal circumstances, little or no net production of hydrogen occurs, however, as the gas is rapidly oxidized by the enzyme uptake hydrogenase in order to recover the reducing equivalent, H+.
In a longer perspective, the Peter Lindblad and his colleagues from the Microbial Chemistry group hope to engineer cyanobacteria that do not recycle the produced hydrogen but liberate the valuable gas. An obvious way to achieve this is to block the uptake hydrogenase, and already in 2004, Peter Lindblad studied hydrogen production in a mutant strain of Nostoc punctiforme that lacks the uptake hydrogenase. This strain, NHM5, produced up to 6 molecules of H2 per molecule of fixed N2 and liberated up to 8.9 µmol (mg of chlorophyll a)-1h-1 of hydrogen compared to virtually no released hydrogen in the wild type strain. Furthermore, since hydrogen release was strongly dependent upon the light, photosynthetic energy may be directed towards hydrogen production rather than nitrogen fixation under the right high-light conditions.
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The free living cells of Synechocystis are in contrast to Nostoc, which is filamentous. From protist.i.hosei.ac.jp
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Certain cyanobacteria, however, contain another bidirectional hydrogenase that can produce hydrogen directly by oxidizing H+ and might have involved in order to get rid of excess reducing equivalents. Peter Lindblad has studied this enzyme in the cyanobacteria Synechocystis and found that hydrogen production is apparently tightly regulated by eg autofeedback, O2 and ATP levels. The enzyme is also regulated at the genetic level and by hydrogenase-specific proteinases, and consequently it will be a major accomplishment to design novel strains of cyanobacteria that can produce large amounts of free hydrogen.
A somewhat different approach to solar fuel generation is taken by Stenbjörn Styring form the Molecular Biomimetics and Photosynthesis Group. He envisions synthetic versions of the cyanobacterial enzymes assembled into a solar fuel generating device - an approach called biomimetics. Such artificial photosynthetic systems have been an inspiration for scientists for many years, but recent developments seem to indicate that integrated light-to-fuels systems are indeed possible.
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A theoretical solar-fuel apparatus combines two synthetic reaction centers that split waters and produce hydrogen, respectively. From www.fotomol.uu.se
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In cooperation with Magnus Anderlund, Olof Johansson and Sascha Ott from the Organic/Organo-metallic Chemistry Group, Stenbjörn Styring is trying to construct synthetic ruthenium-manganese complexes that can mimick the light driven and water splitting reactions known from photosystem II. For light absorption, the scientist use synthetic complexes containing the metal ruthenium in place of chlorophyll. These complexes are less sensitive to damage from excess light and from a chemical point of view they are easy to work with.
Upon light absorption, the ruthenium complex liberates an electron which is taken from its attached manganese complex in a water splitting reaction similar to natural photosynthesis. Back in 2005, Stenbjörn Styring - together with Magnus Borgström and Leif Hammarström from Department of Physical Chemistry at Uppsala University - published such a new 'supermolecule' that were able to extract electrons from water and pass them on to an electron acceptor using light as the energy source. The next step is now to design a biomimetic catalyst that can accept the electrons and - upon light absorption - put them together with protons under formation of free hydrogen gas.
You can find more information about Department of Photochemistry and Molecular Science at the official homepage or in this recent review from the group.
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