| 1. |
- Bailey, S, et al.
(författare)
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Acclimation of Arabidopsis thaliana to the light environment : the existence of separate low light and high light responses
- 2001
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Ingår i: Planta. - 0032-0935 .- 1432-2048. ; 213:5, s. 794-801
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Tidskriftsartikel (refereegranskat)abstract
- The capacity for photosynthetic acclimation in Arabidopsis thaliana (L.) Heynh. cv. Landsberg erecta was assessed during growth over a broad range of irradiance. Discontinuities in the response to growth irradiance were revealed for the light- and CO2-saturated rate of photosynthesis (P-max) and the ratio of chlorophyll a to chlorophyll b (Chl a/b). Three separate phases in the response of P-max and Chl a/b to growth light were evident, with increases at low and high irradiance ranges and a plateau at intermediate irradiance. By measuring all chlorophyll-containing components of the thylakoid membrane that contribute to Chl alb we reveal that distinct strategies for growth at low and high irradiance underlie the discontinuous response. These strategies include, in addition to changes in the major light-harvesting complexes of photosystem II (LHCII) , large shifts in the amounts of both reaction centres as well as significant changes in the levels of minor LHCII and LHCI components.
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| 2. |
- Dahlman, Lena, et al.
(författare)
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Organic and inorganic nitrogen uptake in lichens
- 2004
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Ingår i: Planta. - : Springer. - 0032-0935 .- 1432-2048. ; 219, s. 459-467
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Tidskriftsartikel (refereegranskat)abstract
- In order to learn more about nitrogen (N) acquisition in lichens, and to see whether different lichens differ in their affinity to various N sources, N uptake was measured in 14 various lichen associations (“species”). These species represented various morphologies (fruticose or foliose), contrasting microhabitat preferences (epiphytic or terricolous), and had green algal, cyanobacterial or both forms of photobionts. N was supplied under non-limiting conditions as an amino acid mixture, ammonium, or nitrate, using 15N to quantify uptake. Carbonyl cyanide m-chlorophenylhydrazone (CCCP) was used to separate active and passive uptake. Thallus N, amino acids, soluble polyol concentrations, and the biont-specific markers chlorophyll a and ergosterol were quantified, aiming to test if these metabolites or markers were correlated with N uptake capacity. Ammonium uptake was significantly greater and to a higher extent passive, relative to the other two N sources. Nitrate uptake differed among lichen photobiont groups, cyanobacterial lichens having a lower uptake rate. All lichens had the capacity to assimilate amino acids, in many species at rates equal to nitrate uptake or even higher, suggesting that organic N compounds could potentially have an important role in the N nutrition of these organisms. There were no clear correlations between N uptake rates and any of the measured metabolites or markers. The relative uptake rates of ammonium, nitrate and amino acids were not related to morphology or microhabitat.
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| 3. |
- Heineke, D, et al.
(författare)
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Metabolic response of potato plants to an antisense reduction of the P-protein of glycine decarboxylase
- 2001
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Ingår i: Planta. - 0032-0935 .- 1432-2048. ; 212:5-6, s. 880-887
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Tidskriftsartikel (refereegranskat)abstract
- Potato (Solanum tuberosum L. cv. Desire) plants with reduced amounts of P-protein, one of the subunits of glycine decarboxylase (GDC), have been generated by introduction of an antisense transgene. Two transgenic lines, containing about 60-70% less P-protein in the leaves compared to wild-type potato, were analysed in more detail. The reduction in P-protein amount led to a decrease in the ability of leaf mitochondria to decarboxylate glycine. Photosynthetic and growth rates were reduced but the plants were viable under ambient air and produced tubers. Glycine concentrations within the leaves were elevated up to about 100-fold during illumination. Effects: on other amino acids and on sucrose and hexoses were minor. Nearly all of the glycine accumulated during the day was metabolised during the following night. The data suggest that the GDC operates far below substrate saturation under normal conditions thus allowing a flexible and fast response to changes in the environment.
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| 4. |
- Ivanov, A G, et al.
(författare)
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Photosynthetic electron transport adjustments in overwintering Scots pine (Pinus sylvestris L.)
- 2001
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Ingår i: Planta. - 0032-0935 .- 1432-2048. ; 213:4, s. 575-585
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Tidskriftsartikel (refereegranskat)abstract
- As shown before [C. Ottander et al. (1995) Planta 197:176-183], there is a severe inhibition of the photosystem (PS) II photochemical efficiency of Scots pine (Pinus sylvestris L.) during the winter. In contrast, the in vivo PSI photochemistry is less inhibited during winter as shown by in vivo measurements of DeltaA(820)/Delta (820) (P700(+)). There was also an enhanced cyclic electron transfer around PSI in winter-stressed needles as indicated by 4-fold faster reduction kinetics of P700(+). The differential functional stability of PSII and PSI was accompanied by a 3.7-fold higher intersystem electron pool size, and a 5-fold increase in the stromal electron pool available for P700(+) reduction. There was also a strong reduction of the QB band in the thermoluminescence glow curve and markedly slower Q-A re-oxidation in needles of winter pine, indicating an inhibition of electron transfer between QA and QB. The data presented indicate that the plastoquinone pool is largely reduced in winter pine, and that this reduced state is likely to be of metabolic rather than photochemical origin. The retention of PSI photochemistry, and the suggested metabolic reduction of the plastoquinone pool in winter stressed needles of Scots pine are discussed in terms of the need for enhanced photoprotection of the needles during the winter and the role of metabolically supplied energy for the recovery of photosynthesis from winter stress in evergreens.
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| 5. |
- Ivanov, A G, et al.
(författare)
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Seasonal responses of photosynthetic electron transport in Scots pine (Pinus sylvestris L.) studied by thermoluminescence
- 2002
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Ingår i: Planta. - : Springer Science and Business Media LLC. - 0032-0935 .- 1432-2048. ; 215:3, s. 457-465
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Tidskriftsartikel (refereegranskat)abstract
- The potential of photosynthesis to recover from winter stress was studied by following the thermoluminescence (TL) and chlorophyll fluorescence changes of winter pine needles during the exposure to room temperature (20 degreesC) and an irradiance of 100 mumol m(-2) s(-1). TL measurements of photosystem 11 (PSII) revealed that the S(2)Q(B)(-) charge recombinations (the B-band) were shifted to lower temperatures in winter pine needles, while the S(2)Q(A)(-) recombinations (the Q-band) remained close to 0 degreesC. This was accompanied by a drastically reduced (65%) PSII photochemical efficiency measured as F-v/F-m and a 20-fold faster rate of the fluorescence transient from F-o to F, as compared to summer pine. A strong positive correlation between the increase in the photochemical efficiency of PSII and the increase in the relative contribution of the B-band was found during the time course of the recovery process. The seasonal dynamics of TL in Scots pine needles studied under field conditions revealed that between November and April, the contribution of the Q- and B-bands to the overall TL emission was very low (less than 5%). During spring, the relative contribution of the Q- and B-bands, corresponding to charge recombination events between the acceptor and donor sides of PSII, rapidly increased, reaching maximal values in late July. A sharp decline of the B-band was observed in late summer, followed by a gradual decrease, reaching minimal values in November. Possible mechanisms of the seasonally induced changes in the redox properties Of S-2/S(3)Q(B)(-) recombinations are discussed. It is proposed that the lowered redox potential Of Q(B) in winter needles increases the population Of Q(A)(-). thus enhancing the probability for non-radiative P680(+) Q(A)(-) recombination. This is suggested to enhance the radiationless dissipation of excess light within the PSII reaction center during cold acclimation and during cold winter periods.
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| 6. |
- Lundberg, Peter, et al.
(författare)
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Primary metabolism in N-2-fixing Alnus incana-Frankia symbiotic root nodules studied with N-15 and P-31 nuclear magnetic resonance spectroscopy
- 2004
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Ingår i: Planta. - : Springer Science and Business Media LLC. - 0032-0935 .- 1432-2048. ; 219:4, s. 661-672
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Tidskriftsartikel (refereegranskat)abstract
- The primary nitrogen metabolism of the N-2-fixing root nodule symbiosis Alnus incana (L.)-Frankia was investigated by P-31 and N-15 nuclear magnetic resonance (NMR) spectroscopy. Perfusion of root nodules in a pulse-chase approach with N-15- or N-14-labeled NH4+ revealed the presence of the amino acids alanine (Ala), gamma-amino butyric acid, glutamine (Gln), glutamic acid (Glu), citrulline (Cit) and arginine (Arg). Labeling kinetics of the Gln amide-N and alpha-amino acids suggested that the glutamine synthetase (GS, EC 6.3.1.2)-glutamate synthase (GOGAT, EC 1.4.1.13) pathway was active. Inhibition of the GS-catalyzed reaction by methionine sulphoximine abolished incorporation of N-15. Cit was labeled in all three N positions but most rapidly in the omega position, consistent with carbamoyl phosphate as the precursor to which Gln could be the amino donor catalyzed by carbamoyl phosphate synthase (CPS, EC 6.3.5.5). Ala biosynthesis occurred consistent with a flux of N in the sequence Gln-Glu-Ala. P-31 NMR spectroscopy in vivo and of extracts revealed several metabolites and was used in connection with the N-15 pulse-chase experiment to assess general metabolic status. Stable concentrations of ATP and UDP-glucose during extended perfusions showed that the overall root nodule metabolism appeared undisturbed throughout the experiments. The metabolic pathways suggested by the NMR results were confirmed by high activities of the enzymes GS, NADH-GOGAT and ornithine carbamoyltransferase (OCT, EC 2.1.3.3). We conclude that the primary pathway of NH4+ assimilation in A. incana root nodules occurs through the GS-GOGAT pathway. Biosynthesis of Cit through GS-CPS-OCT is important and is a link between the first amino acid Gln and this final transport and storage form of nitrogen.
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| 7. |
- Savitch, L V, et al.
(författare)
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Cold acclimation of Arabidopsis thaliana results in incomplete recovery of photosynthetic capacity, associated with an increased reduction of the chloroplast stroma
- 2001
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Ingår i: Planta. - 0032-0935 .- 1432-2048. ; 214:2, s. 295-303
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Tidskriftsartikel (refereegranskat)abstract
- The effects of short-term cold stress and long-term cold acclimation on the light reactions of photosynthesis were examined in vivo to assess their contributions to photosynthetic acclimation to low temperature in Arabidopsis thaliana (L.) Heynh.. All photosynthetic measurements were made at the temperature of exposure: 23 degreesC for non-acclimated plants and 5 degreesC for cold-stressed and cold-acclimated plants. Three-day cold-stress treatments at 5 degreesC inhibited light-saturated rates of CO2 assimilation and O-2 evolution by approximately 75%. The 3-day exposure to 5 degreesC also increased the proportion of reduced QA by 50%, decreased the yield of PSII electron transport by 65% and decreased PSI activity by 31%. In contrast, long-term cold acclimation resulted in a strong but incomplete recovery of light-saturated photosynthesis at 5 degreesC. The rates of light-saturated CO2 and O-2 gas exchange and the in vivo yield of PSII activity under light-saturating conditions were only 35-40% lower, and the relative redox state of QA only 20% lower, at 5 degreesC after cold acclimation than in controls at 23 degreesC. PSI activity showed full recovery during long-term cold acclimation. Neither short-term cold stress nor long-term cold acclimation of Arabidopsis was associated with a limitation in ATP, and both treatments resulted in an increase in the ATP/NADPH ratio. This increase in ATP/NADPH was associated with an inhibition of PSI cyclic electron transport but there was no apparent change in the Mehler reaction activity in either cold-stressed or cold-acclimated leaves. Cold acclimation also resulted in an increase in the reduction state of the stroma, as indicated by an increased total activity and activation state of NADP-dependent malate dehydrogenase, and increased light-dependent activities of the major regulatory enzymes of the oxidative pentose-phosphate pathway. We suggest that the photosynthetic capacity during cold stress as well as cold acclimation is altered by limitations at the level of consumption of reducing power in carbon metabolism.
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| 8. |
- Siedlecka, A, et al.
(författare)
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The small subunit ADP-glucose pyrophosphorylase (ApS) promoter mediates okadaic acid-sensitive uidA expression in starch-synthesizing tissues and cells in Arabidopsis
- 2003
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Ingår i: Planta. - : Springer Science and Business Media LLC. - 0032-0935 .- 1432-2048. ; 217:2, s. 184-192
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Tidskriftsartikel (refereegranskat)abstract
- Transgenic plants of Arabidopsis thaliana Heynh., transformed with a bacterial beta-glucuronidase (GUS) gene under the control of the promoter of the small subunit (ApS) of ADP-glucose pyrophosphorylase (AGPase), exhibited GUS staining in leaves (including stomata), stems, roots and flowers. Cross-sections of stems revealed GUS staining in protoxylem parenchyma, primary phloem and cortex. In young roots, the staining was found in the root tips, including the root cap, and in vascular tissue, while the older root-hypocotyl axis showed prominent staining in the secondary phloem and paratracheary parenchyma of secondary xylem. The GUS staining co-localized with ApS protein, as found by tissue printing using antibodies against ApS. Starch was found only in cell and tissue types exhibiting GUS staining and ApS labelling, but not in all of them. For example, starch was lacking in the xylem parenchyma and secondary phloem of the root-hypocotyl axis. Sucrose potently activated ApS gene expression in leaves of wild-type (wt) plants, and in transgenic seedlings grown on sucrose medium where GUS activity was quantified with 4-methylumbelliferyl-beta-glucuronide as substrate. Okadaic acid, an inhibitor of protein phosphatases 1 and 2A, completely blocked expression of ApS in mature leaves of wt plants and prevented GUS staining in root tips and flowers of the transgenic plants, suggesting a similar signal transduction mechanism for ApS expression in various tissues. The data support the key role of AGPase in starch synthesis, but they also underlie the ubiquitous importance of the ApS gene for AGPase function in all organs/tissues of Arabidopsis.
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