| 1. |
- Campeau, A., et al.
(författare)
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Stable Carbon Isotopes Reveal Soil-Stream DIC Linkages in Contrasting Headwater Catchments
- 2018
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Ingår i: Journal of Geophysical Research-Biogeosciences. - : American Geophysical Union (AGU). - 2169-8953 .- 2169-8961. ; 123:1, s. 149-167
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Tidskriftsartikel (refereegranskat)abstract
- Large CO2 evasion to the atmosphere occurs as dissolved inorganic carbon (DIC) is transported from soils to streams. While this physical process has been the focus of multiple studies, less is known about the underlying biogeochemical transformations that accompany this transfer of C from soils to streams. Here we used patterns in stream water and groundwater C-13-DIC values within three headwater catchments with contrasting land cover to identify the sources and processes regulating DIC during its transport. We found that although considerable CO2 evasion occurs as DIC is transported from soils to streams, there were also other processes affecting the DIC pool. Methane production and mixing of C sources, associated with different types and spatial distribution of peat-rich areas within each catchment, had a significant influence on the C-13-DIC values in both soils and streams. These processes represent an additional control on C-13-DIC values and the catchment-scale cycling of DIC across different northern landscape types. The results from this study demonstrate that the transport of DIC from soils to streams results in more than just rapid CO2 evasion to the atmosphere but also represents a channel of C transformation, which questions some of our current conceptualizations of C cycling at the landscape scale. Plain Language Summary Large carbon dioxide emission to the atmosphere occurs as rainwater percolates through soils and into streams. This physical process is important for the global carbon cycle and has been the focus of multiple studies. However, less is known about the underlying processes that accompanies this transfer of carbon dioxide from soils to streams. Here we analyze the stable isotope composition of soil and stream carbon dioxide and demonstrate that methane production and mixing of carbon sources also occur in soils and streams. These processes were linked to different types and configurations of peat-rich areas, for example, bogs, fens, and riparian zones, found within each of the three studied catchments. Our results therefore demonstrate that the export of carbon dioxide from soils to streams not only results in emissions to the atmosphere but also represents a channel of transformation. This questions some of our current conceptualization of the catchment-scale cycling of carbon dioxide.
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| 2. |
- Christensen, Torben, et al.
(författare)
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Biotic controls on CO2 and CH4 exchange in wetlands - a closed environment study
- 2003
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Ingår i: Biogeochemistry. - 0168-2563 .- 1573-515X. ; 64:3, s. 337-354
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Tidskriftsartikel (refereegranskat)abstract
- Wetlands are significant sources of the important greenhouse gas CH4. Here we explore the use of an experimental system developed for the determination of continuous fluxes of CO2 and CH4 in closed ecosystem monoliths including the capture of (CO2)-C-14 and (CH4)-C-14 following pulse labelling with (CO2)-C-14. We show that, in the ecosystem studied, ebullition (bubble emission) may account for 18 to 50% of the total CH4 emission, representing fluxes that have been difficult to estimate accurately in the past. Furthermore, using plant removal and C-14 labelling techniques, we use the system to detail the direct influence of vascular plants on CH4 emission. This influence is observed to be dependent on the amount of vascular plants present. The results that may be produced using the presented experimental set-up have implications for an improved understanding of wetland ecosystem/atmosphere interactions, including possible feedback effects on climate change. In recent years much attention has been devoted to ascertaining and subsequently using the relationship between net ecosystem productivity and CH4 emission as a basis for extrapolation of fluxes across large areas. The experimental system presented may be used to study the complex relationship between vascular plants and CH4 emission and here we show examples of how this may vary considerably in nature between and even within ecosystems.
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| 3. |
- HUNER, NPA, et al.
(författare)
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PHOTOSYNTHESIS, PHOTOINHIBITION AND LOW-TEMPERATURE ACCLIMATION IN COLD TOLERANT PLANTS
- 1993
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Ingår i: Photosynthesis Research. - 0166-8595 .- 1573-5079. ; 37:1, s. 19-39
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Tidskriftsartikel (refereegranskat)abstract
- Cold acclimation requires adjustment to a combination of light and low temperature, conditions which are potentially photoinhibitory. The photosynthetic response of plants to low temperature is dependent upon time of exposure and the developmental history of the leaves. Exposure of fully expanded leaves of winter cereals to short-term, low temperature shifts inhibits whereas low temperature growth stimulates electron transport capacity and carbon assimilation. However, the photosynthetic response to low temperature is clearly species and cultivar dependent. Winter annuals and algae which actively grow and develop at low temperature and moderate irradiance acquire a resistance to irradiance 5- to 6-fold higher than their growth irradiance. Resistance to short-term photoinhibition (hours) in winter cereals is a reflection of the increased capacity to keep Q(A) oxidized under high light conditions and low temperature. This is due to an increased capacity for photosynthesis. These characteristics reflect photosynthetic acclimation to low growth temperature and can be used to predict the freezing tolerance of cereals. It is proposed that the enhanced photosynthetic capacity reflects an increased flux of fixed carbon through to sucrose in source tissue as a consequence of the combined effects of increased storage of carbohydrate as fructans in the vacuole of leaf mesophyll cells and an enhanced export to the crown due to its increased sink activity. Long-term exposure (months) of cereals to low temperature photoinhibition indicates that this reduction of photochemical efficiency of PS II represents a stable, long-term down regulation of PS II to match the energy requirements for CO2 fixation. Thus, photoinhibition in vivo should be viewed as the capacity of plants to adjust photosynthetically to the prevailing environmental conditions rather than a process which necessarily results in damage or injury to plants. Not all cold tolerant, herbaceous annuals use the same mechanism to acquire resistance to photoinhibition. In contrast to annuals and algae, overwintering evergreens become dormant during the cold hardening period and generally remain susceptible to photoinhibition. It is concluded that the photosynthetic response to low temperatures and susceptibility to photoinhibition are consequences of the overwintering strategy of the plant species.
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| 4. |
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| 5. |
- Oquist, M. G., et al.
(författare)
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Nitrification controls N2O production rates in a frozen boreal forest soil
- 2007
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Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 39:7, s. 1809-1811
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Tidskriftsartikel (refereegranskat)abstract
- The winter season has been identified as a significant contributor to N2O emissions from boreal soils, but our understanding of the processes regulating these emissions is fragmentary. We investigated potential N-sources and pathways involved in N2O formation in a frozen boreal forest soil by labeling soil samples with N-15-containing substrates, and measured rates of (N2O)-N-15/N-15(2) formation under both oxic and anoxic conditions. Our results showed that all N2O produced in the frozen samples originate from denitrification, but the rate-limiting factor is NO3- availability, which is largely governed by nitrification. This suggests that N2O formation in frozen boreal soils may be sustained for a prolonged period of time, but is governed by a delicate balance of the O-2 regime. (c) 2007 Elsevier Ltd. All rights reserved.
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| 6. |
- Oquist, M. G., et al.
(författare)
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Nitrous oxide production in a forest soil at low temperatures - processes and environmental controls
- 2004
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Ingår i: Fems Microbiology Ecology. - : Oxford University Press (OUP). - 0168-6496 .- 1574-6941. ; 49:3, s. 371-378
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Tidskriftsartikel (refereegranskat)abstract
- Recent investigations have highlighted the relative importance of the winter season for emissions of N2O from boreal soils. However, our understanding of the processes and environmental controls regulating these emissions is fragmentary. Therefore, we investigated the potential for, and relative importance of, N2O formation at temperatures below 0 degreesC in laboratory experiments involving incubations of a Swedish boreal forest soil. Our results show that frozen soils have a high potential for N2O formation and subsequent emission. Net N2O production rates at -4 degreesC equaled those observed at +10 to +15 degreesC at moisture contents >60% of the soil's water-holding capacity. The source of this N2O was found to be denitrification occurring in anoxic microsites in the frozen soil and temperature per se did not control the denitrification rates at temperatures around 0 degreesC. Furthermore, both net nitrogen-mineralisation and nitrification were observed in the frozen soil samples. Based on these findings we propose a conceptual model for the temperature response of N2O formation in soils at low temperatures. (C) 2004 Federation of European Microbiological Societies. Published by Elsevier B.V. All rights reserved.
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| 7. |
- Sparrman, Tobias, et al.
(författare)
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Quantifying unfrozen water in frozen soil by high-field H-2 NMR
- 2004
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Ingår i: Environmental Science & Technology. - 0013-936X. ; 38:20, s. 5420-5425
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Tidskriftsartikel (refereegranskat)abstract
- To understand wintertime controls of biogeochemical processes in high latitude soils it is essential to distinguish between direct temperature effects and the effects of changes in water availability mediated by freezing. Efforts to separate these controls are hampered by a lack of adequate methods to determine the proportion of unfrozen water. In this study we present a high-field (H2O)-H-2 NMR method for quantifying unfrozen water content in frozen soil. The experimental material consisted of the humic layer of a boreal spruce forest soil mixed with varying proportions of quartz sand and humidified with deuterium-enriched water. The relative standard deviation of unfrozen water content (measured as NMR signal integral) was less than 2% for repeated measurements on a given sample and 3.5% among all samples, based on a total of 16 measurements. As compared to H-1 NMR, this H-2 NMR method was found to be superior for several reasons: it is less sensitive to field inhomogeneity and paramagnetic impurities, it gives a bigger line shape difference between the ice and liquid signal, it shows a sharper response to water fusion, and it excludes the possibility of hydrogen in the organic material interfering with the measurement.
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| 8. |
- Borodich, A, et al.
(författare)
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Segregation of the photosystems in higher plant thylakoids and short- and long-term regulation by a mesoscopic approach
- 2003
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Ingår i: Journal of Theoretical Biology. - 0022-5193 .- 1095-8541. ; 225:4, s. 431-441
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we consider the relationship between the lateral segregation of photosystems I and II in the grana and characteristics of the short- and long-term regulation in thylakoids following the mesoscopic approach. Our study is thermodynamic; it is based on the Flory-Huggins theory for binary mixtures and the McMillan-Mayer theory of heterogeneous solutions. We demonstrate that state transitions promote rearrangement of photosystems by either favoring their mixing after LHCII phosphorylation or enhancing their segregation after LHCII dephosphorylation. This regulation influences the entire system properties locally. We also demonstrate that the variations of the photosystem ratio promote rearrangement of the photosystems preserving their segregation. This regulation influences the entire system properties globally. The studies presented are another indication of the importance of the segregation of the photosystems in the grana thylakoids of higher plants. Segregation of PSIs and PSIIs is a signature of the spinodal decomposition, which is a fine regulatory mechanism, related to both the short- and long-term adaptations of the photosynthetic apparatus in higher plant thylakoids. (C) 2003 Elsevier Ltd. All rights reserved.
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| 9. |
- Borodich, A, et al.
(författare)
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Segregation of the photosystems in thylakoids depends on their size
- 2003
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Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - 0005-2728 .- 1879-2650. ; 1606:1-3, s. 73-82
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Tidskriftsartikel (refereegranskat)abstract
- Lateral segregation of two types of photosystems in thylakoid membranes of green plants is one of the key factors that provide the stability and fine-tuning of the light quanta supply by pigment proteins and non-cyclic electron transport. Due to this specific feature of the membrane structural organization, the photosynthetic units function in the green plants with optimal performance. In this report a mesoscopic theory is outlined to address the physical aspects of segregation phenomenon. Results of theoretical studies and computer simulations suggest that charge mismatch and the size difference between two photosystems in grana are most responsible for their lateral segregation, which is driven by the screened electrostatic and lipid-induced interactions. Comparative simulations of photosystems of different sizes show the crucial dependence of their ordering on a geometrical parameter. It seems that the size effect alone may prevent photosystems from segregated arrangement in cyanobacterial thylakoids. (C) 2003 Elsevier B.V. All rights reserved.
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| 10. |
- HURRY, VM, 1960-, et al.
(författare)
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EFFECT OF LONG-TERM PHOTOINHIBITION ON GROWTH AND PHOTOSYNTHESIS OF COLD-HARDENED SPRING AND WINTER-WHEAT
- 1992
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Ingår i: Planta. - 0032-0935 .- 1432-2048. ; 188:3, s. 369-375
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Tidskriftsartikel (refereegranskat)abstract
- The effect of repeated exposure to high light (1200 mumol . m-2 . s-1 photosynthetic photon flux density, PPFD) at 5-degrees-C was examined in attached leaves of cold-grown spring (cv. Katepwa) and winter (cv. Kharkov) wheat (Triticum aestivum L.) over an eight-week period. Under these conditions, Kharkov winter wheat exhibited a daily reduction of 24% in F(V)/F(M) (the ratio of variable to maximal fluorescence in the dark-adapted state), in contrast to 41% for cold-grown Katepwa spring wheat. Both cultivars were able to recover from this daily suppression of F(V)/F(M) such that the leaves exhibited an average morning F(V)/F(M) of 0.651 +/- 0.004. Fluorescence measurements made under steady-state conditions as a function of irradiance from 60 to 2000 mumol . m-2 . s-1 indicated that the yield of photosystem II (PSII) electron transport under light-saturating conditions was the same for photoinhibited and control cold-grown plants, regardless of cultivar. Repeated daily exposure to high light at low temperature did not increase resistance to short-term photoinhibition, although zeaxanthin levels increased by three- to fourfold. In addition, both cultivars increased the rate of dry-matter accumulation, relative to control plants maintained at 5-degrees-C and 250 mumol . m-2 . s-1 PPFD (10% and 28% for Katepwa and Kharkov, respectively), despite exhibiting suppressed F(V)/F(M) and reduced photon yields for O2 evolution following daily high-light treatments. Thus, although photosynthetic efficiency is suppressed by a long-term, photoinhibitory treatment, light-saturated rates of photosynthesis are sufficiently high during the high-light treatment to offset any reduction in photochemical efficiency of PSII. We suggest that in these cold-tolerant plants, photoinhibition of PSII may represent a long-term, stable, down-regulation of photochemistry to match the overall photosynthetic demand for ATP and reducing equivalents.
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| 11. |
- Ivanov, A G, et al.
(författare)
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Low-temperature modulation of the redox properties of the acceptor side of photosystem II : photoprotection through reaction centre quenching of excess energy
- 2003
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Ingår i: Physiologia Plantarum. - 0031-9317 .- 1399-3054. ; 119:3, s. 376-383
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Tidskriftsartikel (refereegranskat)abstract
- Although it has been well established that acclimation to low growth temperatures is strongly correlated with an increased proportion of reduced Q(A) in all photosynthetic groups, the precise mechanism controlling the redox state of Q(A) and its physiological significance in developing cold tolerance in photoautotrophs has not been fully elucidated. Our recent thermoluminescence (TL) measurements of the acceptor site of PSII have revealed that short-term exposure of the cyanobacterium Synechococcus sp. PCC 7942 to cold stress, overwintering of Scots pine (Pinus sylvestris L.), and acclimation of Arabidopsis plants to low growth temperatures, all caused a substantial shift in the characteristic T-M of S(2)Q(B)(-) recombination to lower temperatures. These changes were accompanied by much lower overall TL emission, restricted electron transfer between Q(A) and Q(B), and in Arabidopsis by a shift of the S(2)Q(A)(-)-related peak to higher temperatures. The shifts in recombination temperatures are indicative of a lower activation energy for the S(2)Q(B)(-) redox pair and a higher activation energy for the S(2)Q(A)(-) redox pair. This results in an increase in the free-energy gap between P680(+)Q(A)(-) and P680(+)Pheo(-) and a narrowing of the free energy gap between Q(A) and Q(B) electron acceptors. We propose that these effects result in an increased population of reduced Q(A) (Q(A)(-)), facilitating non-radiative P680(+)Q(A)(-) radical pair recombination within the PSII reaction centre. The proposed reaction centre quenching could be an important protective mechanism in cyanobacteria in which antenna and zeaxanthin cycle-dependent quenching are not present. In herbaceous plants, the enhanced capacity for dissipation of excess light energy via PSII reaction centre quenching following cold acclimation may complement their capacity for increased utilization of absorbed light through CO2 assimilation and carbon metabolism. During overwintering of evergreens, when photosynthesis is inhibited, PSII reaction centre quenching may complement non-photochemical quenching within the light-harvesting antenna when zeaxanthin cycle-dependent energy quenching is thermodynamically restricted by low temperatures. We suggest that PSII reaction centre quenching is a significant mechanism enabling cold-acclimated organisms to acquire increased resistance to high light.
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| 12. |
- KROL, M, et al.
(författare)
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CHLOROPHYLL A/B-BINDING PROTEINS, PIGMENT CONVERSIONS, AND EARLY LIGHT-INDUCED PROTEINS IN A CHLOROPHYLL B-LESS BARLEY MUTANT
- 1995
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Ingår i: Plant Physiology. - 0032-0889 .- 1532-2548. ; 107:3, s. 873-883
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Tidskriftsartikel (refereegranskat)abstract
- Monospecific polyclonal antibodies have been raised against synthetic peptides derived from the primary sequences from different plant light-harvesting Chl a/b-binding (LHC) proteins. Together with other monospecific antibodies, these were used to quantify the levels of the 10 different LHC proteins in wild-type and chlorina 12 barley (Hordeum vulgare L.), grown under normal and intermittent light (ImL). Chlorina 12, grown under normal light, lacked Lhcb1 (type I LHC II) and Lhcb6 (CP24) and had reduced amounts of Lhcb2, Lhcb3 (types II and III LHC II), and Lhcb4 (CP 29). Chlorina f2 grown under ImL lacked all LHC proteins, whereas wild-type ImL plants contained Lhcb5 (CP 26) and a small amount of Lhcb2. The chlorina f2 ImL thylakoids were organized in large parallel arrays, but wild-type ImL thylakoids had appressed regions, indicating a possible role for Lhcb5 in grana stacking. Chlorina f2 grown under ImL contained considerable amounts of violaxanthin (2-3/reaction center), representing a pool of phototransformable xanthophyll cycle pigments not associated with LHC proteins. Chlorina f2 and the plants grown under ImL also contained early light-induced proteins (ELIPs) as monitored by western blotting. The levels of both ELIPs and xanthophyll cycle pigments increased during a 1 h of high light treatment, without accumulation of LHC proteins. These data are consistent with the hypothesis that ELIPs are pigment-binding proteins, and we suggest that ELIPs bind photoconvertible xanthophylls and replace ''normal'' LHC proteins under conditions of light stress.
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| 13. |
- KROL, M, et al.
(författare)
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LOW-TEMPERATURE STRESS AND PHOTOPERIOD AFFECT AN INCREASED TOLERANCE TO PHOTOINHIBITION IN PINUS-BANKSIANA SEEDLINGS
- 1995
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Ingår i: Canadian Journal of Botany. - 0008-4026 .- 1480-3305. ; 73:8, s. 1119-1127
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Tidskriftsartikel (refereegranskat)abstract
- The capacity to develop tolerance to photoinhibition of photosynthesis was assessed in jack pine seedlings (Pinus banksiana Lamb.). Photoinhibition induced at 5 degrees C in control jack pine seedlings grown at 20 degrees C was saturated above an irradiance of 1000 mu mol . m(-2). s(-1) but was detectable at an irradiance as low as 25 mu mol . m(-2). s(-1). However, 20 degrees C seedlings shifted to 5 degrees C were 2-fold more tolerant to photoinhibition than 20 degrees C unshifted control seedlings, as detected by either the light-dependent decrease in photochemical efficiency or the apparent quantum yield of O-2 evolution. The extent of this tolerance of photoinhibition was dependent upon time, photoperiod, and irradiance during exposure to the low-temperature shift. Furthermore, the tolerance of photoinhibition was correlated with anthocyanin accumulation in 20 degrees C grown seedlings shifted to 5 degrees C. In addition, seedlings shifted to 5 degrees C and an 8-h photoperiod exhibited a 2-fold higher yield of photosystem II electron transport, which was associated with an increased capacity to keep Q(A), the first stable quinone electron acceptor of photosystem II, oxidized at high irradiance. This was consistent with a 2-fold higher rate of photosynthesis on a chlorophyll basis. We propose that the combination of light attenuation by anthocyanin in the epidermis and enhanced rates of photosynthesis may, in part, account for the reduced sensitivity of jack pine to photoinhibition at low temperature.
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| 14. |
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| 15. |
- Rojdestvenski, I, et al.
(författare)
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A two-dimensional many-body system with competing interactions as a model for segregation of photosystems in thylakoids of green plants
- 2000
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Ingår i: European Biophysics Journal. - 0175-7571 .- 1432-1017. ; 29:3, s. 214-220
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Tidskriftsartikel (refereegranskat)abstract
- We address the segregation of photosystems I (PSI) and II (PSII) in thylakoid membranes by means of a molecular dynamics method. We assume a two-dimensional (in-plane) problem with PSI and PSII being represented by particles with different values of negative charge. The pair interactions between particles include a screened Coulomb repulsive part and am exponentially decaying attractive part. Our modeling results suggest that the system may have a complicated phase behavior, including a quasi-crystalline phase at low ionic screenmg, a disordered phase and: in addition, a possible "clotting" agglomerate phase at high screening where the photosystems tend to clot together. The relevance of the observed phenomena to the stacking of thylakoid membranes is discussed.
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| 16. |
- Rojdestvenski, I, et al.
(författare)
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Robustness and time-scale hierarchy in biological systems
- 1999
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Ingår i: Biosystems (Amsterdam. Print). - 0303-2647 .- 1872-8324. ; 50:1, s. 71-82
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Tidskriftsartikel (refereegranskat)abstract
- This study addresses the issue of robustness of biological systems with respect to microscopic parameters, especially the emergence of robustness as a consequence of lime-scale hierarchy, applying naive thermodynamic and dynamic assumptions. Theoretical considerations of how the time-scale hierarchy can decouple physiological regulatory mechanisms are illustrated by two model systems involving the photosynthetic apparatus of green plants. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.
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| 17. |
- Rojdestvenski, I, et al.
(författare)
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Segregation of photosystems in thylakoid membranes as a critical phenomenon
- 2002
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Ingår i: Biophysical Journal. - 0006-3495 .- 1542-0086. ; 82:4, s. 1719-1730
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Tidskriftsartikel (refereegranskat)abstract
- The distribution of the two photosystems, PSI and PSII, in grana and stroma lamellae of the chloroplast membranes is not uniform. PSII are mainly concentrated in grana and PSI in stroma thylakoids. The dynamics and factors controlling the spatial segregation of PSI and PSII are generally not well understood, and here we address the segregation of photosystems in thylakoid membranes by means of a molecular dynamics method. The lateral segregation of photosystems was studied assuming a model comprising a two-dimensional (in-plane), two-component, many-body system with periodic boundary conditions and competing interactions between the photosystems in the thylakoid membrane. PSI and PSII are represented by particles with different values of negative charge. The pair interactions between particles include a screened Coulomb repulsive part and an exponentially decaying attractive part. The modeling results suggest a complicated phase behavior of the system, including quasi-crystalline phase of randomly distributed complexes of PSII and PSI at low ionic screening, well defined clustered state of segregated complexes at high screening, and in addition, an intermediate agglomerate phase where the photosystems tend to aggregate together without segregation. The calculations demonstrated that the ordering of photosystems within the membrane was the result of interplay between electrostatic and lipid-mediated interactions. At some values of the model parameters the segregation can be represented visually as well as by analyzing the correlation functions of the configuration.
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| 18. |
- Rojdestvenski, I, et al.
(författare)
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Thermodynamics of complexity
- 2003
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Ingår i: Physica A. - 0378-4371 .- 1873-2119. ; 320, s. 318-328
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Tidskriftsartikel (refereegranskat)abstract
- The definition of complexity, simultaneously introduced by Kolmogorov and Chaitin, has given a numerical measure to what was previously defined only at an intuitive level. This measure, useful as it is, becomes hard to utilise when one deals with the complexity of most real systems, and biological objects in particular. We try to overcome this difficulty by discussing a possible thermodynamic definition of complexity based on energy balance. The Kolmogorov-Chaitin definition of complexity thus relates to our thermodynamic definition in a similar way as the probabilistic definition of entropy relates to the thermodynamic one. In the framework of this intuitive treatment it is discussed how the complexity of a biological system may depend on the variability of the environmental conditions. A specific illustration of this approach is given using some numerical modeling examples. (C) 2002 Elsevier Science B.V. All rights reserved.
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| 19. |
- Savitch, L V, et al.
(författare)
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Two different strategies for light utilization in photosynthesis in relation to growth and cold acclimation
- 2002
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Ingår i: Plant, Cell and Environment. - 0140-7791 .- 1365-3040. ; 25:6, s. 761-771
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Tidskriftsartikel (refereegranskat)abstract
- Seedlings of Lodgepole pine (Pinus contorta L.) and winter wheat (Triticum aestivum L. cv. Monopol) were cold acclimated under controlled conditions to induce frost hardiness. Lodgepole pine responded to cold acclimation by partial inhibition of photosynthesis with an associated partial loss of photosystem II reaction centres, and a reduction in needle chlorophyll content. This was accompanied by a low daily carbon gain, and the development of a high and sustained capacity for non-photochemical quenching of absorbed light. This sustained dissipation of absorbed light as heat correlated with an increased de-epoxidation of the xanthophyll cycle pigments forming the quenching forms antheraxanthin and zeaxanthin. In addition, the PsbS protein known to bind chlorophyll and the xanthophyll cycle pigments increased strongly during cold acclimation of pine. In contrast, winter wheat maintained high photosynthetic rates, showed no loss of chlorophyll content per leaf area, and exhibited a high daily carbon gain and a minimal non-photochemical quenching after cold acclimation. In accordance, cold acclimation of wheat neither increased the de-epoxidation of the xanthophylls nor the content of the PsbS protein. These different responses of photosynthesis to cold acclimation are correlated with pine, reducing its need for assimilates when entering dormancy associated with termination of primary growth, whereas winter wheat maintains a high need for assimilates as it continues to grow and develop throughout the cold-acclimation period. It appears that without evolving a sustained ability for controlled dissipation of absorbed light as heat throughout the winter, winter green conifers would not have managed to adapt and establish themselves so successfully in the cold climatic zones of the northern hemisphere.
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| 20. |
- Soitamo, A J, et al.
(författare)
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Over-production of the D1:2 protein makes Synechococcus cells more tolerant to photoinhibition of Photosystem II
- 1996
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Ingår i: Plant Molecular Biology. - 0167-4412 .- 1573-5028. ; 30:3, s. 467-478
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Tidskriftsartikel (refereegranskat)abstract
- Over-expression of the psbAIII gene encoding for the D1 protein (form II; D1:2) of the photosystem II reaction centre in the Synechococcus sp. PCC 7942 was studied using a inc promoter and the lacI(Q) system. Over-expression was induced with 40 mu g/ml IPTG in the growth medium for either 6 or 12 h at growth irradiance (50 mu mol photons m(-2) s(-1)). This treatment doubled the amount of psbAII/III mRNA and the D1:2 protein in membranes but decreased the amount of psbAI messages and the D1:1 protein. The total amount of both heterodimeric reaction centre proteins, D1 and D2, remained constant under growth light conditions, indicating that the number of PSII centres in the membranes was not affected, only the form of the D1 protein was changed from D1:1 to D1:2 in most centres, When the cells were photoinhibited either at 500 or 1000 mu mol photons m(-2) s(-1), in the presence or absence of the protein synthesis inhibitor lincomycin, the D1:2 protein remained at a higher level in cells in which over-expression had been induced by IPTG. These cells were also less prone to photoinhibition of PSII. It is suggested that the tolerance of cells to photoinhibition increases when most PSII reaction centres contain the D1:2 protein at the beginning of high irradiance. This tolerance is further strengthened by maintaining psbAIII gene over-expression during the photoinhibitory treatment.
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| 21. |
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| 22. |
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| 23. |
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| 24. |
- SUNDBLAD, LG, et al.
(författare)
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PREDICTION OF FROST HARDINESS IN SEEDLINGS OF SCOTS PINE (PINUS-SYLVESTRIS) USING MULTIVARIATE-ANALYSIS OF CHLOROPHYLL-A FLUORESCENCE AND LUMINESCENCE KINETICS
- 1990
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Ingår i: Canadian Journal of Forest Research. - : Canadian Science Publishing. - 0045-5067 .- 1208-6037. ; 20:5, s. 592-597
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Tidskriftsartikel (refereegranskat)abstract
- Seedlings of Scots pine (Pinussylvestris L.) were artificially frost hardened under controlled conditions. To follow the development of hardiness, the frost killing temperature was determined. Four levels of hardiness were defined during the course of frost hardening. After adaptation of the seedlings to dark conditions at room temperature, fluorescence induction and far red induced luminescence decay kinetics were recorded for seedlings of the four defined levels of hardiness. The induction curve of fluorescence and the decay curve of luminescence were digitized for 110 time intervals, and the values were used in a multivariate partial least squares analysis to evaluate the potential of luminescence and fluorescence as predictive probes for cold hardiness. The results showed that both fluorescence induction and luminescence decay kinetics contain information allowing the prediction of frost hardiness of artificially cold-hardened seedlings of Scots pine.
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