| 1. |
- Shutova, Tatiana, 1964-, et al.
(författare)
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The photosystem II-associated Cah3 in Chlamydomonas enhances the O-2 evolution rate by proton removal
- 2008
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Ingår i: EMBO Journal. - : Wiley. - 0261-4189 .- 1460-2075. ; 27:5, s. 782-791
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Tidskriftsartikel (refereegranskat)abstract
- Water oxidation in photosystem II ( PSII) is still insufficiently understood and is assumed to involve HCO3-. A Chlamydomonas mutant lacking a carbonic anhydrase associated with the PSII donor side shows impaired O-2 evolution in the absence of HCO3-. The O-2 evolution for saturating, continuous illumination (R-O2) was slower than in the wild type, but was elevated by HCO3- and increased further by Cah3. The R-O2 limitation in the absence of Cah3/HCO3- was amplified by H2O/D2O exchange, but relieved by an amphiphilic proton carrier, suggesting a role of Cah3/HCO3- in proton translocation. Chlorophyll fluorescence indicates a Cah3/HCO3- effect at the donor side of PSII. Time-resolved delayed fluorescence and O-2-release measurements suggest specific effects on proton-release steps but not on electron transfer. We propose that Cah3 promotes proton removal from the Mn complex by locally providing HCO3-, which may function as proton carrier. Without Cah3, proton removal could become rate limiting during O-2 formation and thus, limit water oxidation under high light. Our results underlie the general importance of proton release at the donor side of PSII during water oxidation.
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| 2. |
- Zabelina, Svetlana A., et al.
(författare)
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Carbon emission from thermokarst lakes in NE European tundra
- 2021
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Ingår i: Limnology and Oceanography. - : John Wiley & Sons. - 0024-3590 .- 1939-5590. ; 66:S1, s. S216-S230
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Tidskriftsartikel (refereegranskat)abstract
- Emission of greenhouse gases (GHGs) from inland waters is recognized as highly important and an understudied part of the terrestrial carbon (C) biogeochemical cycle. These emissions are still poorly quantified in subarctic regions that contain vast amounts of surface C in permafrost peatlands. This is especially true in NE European peatlands, located within sporadic to discontinuous permafrost zones which are highly vulnerable to thaw. Initial measurements of C emissions from lentic waters of the Bolshezemelskaya Tundra (BZT; 200,000 km2) demonstrated sizable CO2 and CH4 concentrations and fluxes to the atmosphere in 98 depressions, thaw ponds, and thermokarst lakes ranging from 0.5 × 106 to 5 × 106 m2 in size. CO2 fluxes decreased by an order of magnitude as waterbody size increased by > 3 orders of magnitude while CH4 fluxes showed large variability unrelated to lake size. By using a combination of Landsat‐8 and GeoEye‐1 images, we determined lakes cover 4% of BZT and thus calculated overall C emissions from lentic waters to be 3.8 ± 0.65 Tg C yr−1 (99% C‐CO2, 1% C‐CH4), which is two times higher than the lateral riverine export. Large lakes dominated GHG emissions whereas small thaw ponds had a minor contribution to overall water surface area and GHG emissions. These data suggest that, if permafrost thaw in NE Europe results in disappearance of large thermokarst lakes and formation of new small thaw ponds and depressions, GHG emissions from lentic waters in this region may decrease.
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