| 1. |
- Andersson, Anders, et al.
(författare)
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A transcriptional timetable of autumn senescence
- 2004
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Ingår i: Genome Biology. - : Springer Science and Business Media LLC. - 1465-6906 .- 1474-760X. ; 5:4, s. R24-
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Tidskriftsartikel (refereegranskat)abstract
- Background We have developed genomic tools to allow the genus Populus (aspens and cottonwoods) to be exploited as a full-featured model for investigating fundamental aspects of tree biology. We have undertaken large-scale expressed sequence tag (EST) sequencing programs and created Populus microarrays with significant gene coverage. One of the important aspects of plant biology that cannot be studied in annual plants is the gene activity involved in the induction of autumn leaf senescence. Results On the basis of 36,354 Populus ESTs, obtained from seven cDNA libraries, we have created a DNA microarray consisting of 13,490 clones, spotted in duplicate. Of these clones, 12,376 (92%) were confirmed by resequencing and all sequences were annotated and functionally classified. Here we have used the microarray to study transcript abundance in leaves of a free-growing aspen tree (Populus tremula) in northern Sweden during natural autumn senescence. Of the 13,490 spotted clones, 3,792 represented genes with significant expression in all leaf samples from the seven studied dates. Conclusions We observed a major shift in gene expression, coinciding with massive chlorophyll degradation, that reflected a shift from photosynthetic competence to energy generation by mitochondrial respiration, oxidation of fatty acids and nutrient mobilization. Autumn senescence had much in common with senescence in annual plants; for example many proteases were induced. We also found evidence for increased transcriptional activity before the appearance of visible signs of senescence, presumably preparing the leaf for degradation of its components.
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| 2. |
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| 3. |
- Andersson, Martin E, et al.
(författare)
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Structural and mutational studies of the carboxylate cluster in iron-free ribonucleotide reductase R2.
- 2004
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Ingår i: Biochemistry. - 0006-2960. ; 43:24, s. 7966-72
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Tidskriftsartikel (refereegranskat)abstract
- The R2 protein of ribonucleotide reductase features a di-iron site deeply buried in the protein interior. The apo form of the R2 protein has an unusual clustering of carboxylate side chains at the empty metal-binding site. In a previous study, it was found that the loss of the four positive charge equivalents of the diferrous site in the apo protein appeared to be compensated for by the protonation of two histidine and two carboxylate side chains. We have studied the consequences of removing and introducing charged residues on the local hydrogen-bonding pattern in the region of the carboxylate cluster of Corynebacterium ammoniagenes and Escherichia coli protein R2 using site-directed mutagenesis and X-ray crystallography. The structures of the metal-free forms of wild-type C. ammoniagenes R2 and the mutant E. coli proteins D84N, S114D, E115A, H118A, and E238A have been determined and their hydrogen bonding and protonation states have been structurally assigned as far as possible. Significant alterations to the hydrogen-bonding patterns, protonation states, and hydration is observed for all mutant E. coli apo proteins as compared to wild-type apo R2. Further structural variations are revealed by the wild-type apo C. ammoniagenes R2 structure. The protonation and hydration effects seen in the carboxylate cluster appear to be due to two major factors: conservation of the overall charge of the site and the requirement of electrostatic shielding of clustered carboxylate residues. Very short hydrogen-bonding distances between some protonated carboxylate pairs are indicative of low-barrier hydrogen bonding.
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| 4. |
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| 5. |
- Andersson, Ove, et al.
(författare)
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An ice phase of lowest thermal conductivity
- 2004
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 120:20, s. 9612-9617
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Tidskriftsartikel (refereegranskat)abstract
- On pressurizing at temperatures near 130 K, hexagonal and cubic ices transform implosively at 0.8–1 GPa. The phase produced on transformation has the lowest thermal conductivity among the known crystalline ices and its value decreases on increase in temperature. An ice phase of similar thermal conductivity is produced also when high-density amorphous ice kept at 1 GPa transforms on slow heating when the temperature reaches ∼155 K. These unusual formation conditions, the density and its distinguished thermal conductivity, all indicate that a distinct crystal phase of ice has been produced.
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| 6. |
- Andersson, Ove, et al.
(författare)
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Spontaneous transformation of water's high-density amorph and a two-stage crystallization to ice VI at 1 GPa : a dielectric study
- 2004
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 120:24, s. 11662-11671
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Tidskriftsartikel (refereegranskat)abstract
- Dielectric relaxation spectra of a metastable crystal phase formed on implosive and exothermic transformation of pressure-amorphized hexagonal ice have been measured in situ at 0.97 GPa pressure over a range of temperature. The metastable phase showed no relaxation peak at 130 K and 0.97 GPa. When heated at a fixed pressure of 0.97 GPa, it began to transform at ∼ 145 K exothermally to a phase whose relaxation rate and equilibrium dielectric permittivity increased. A second, but slower exothermic transformation also occurred at ∼ 175 K. After keeping at 213 K, the relaxation rate and equilibrium permittivity reached the known values of these two quantities for ice VI. Thus the metastable phase transformed to ice VI in two stages. It is conjectured that the intermediate phase in this transformation could be ice XII. The rate of transformation is not determined by the reorientational relaxation rate of water molecules in the ices
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| 7. |
- Andersson, Ove, et al.
(författare)
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Time-dependent amorphization of ice at 0.8-0.9 GPa
- 2004
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Ingår i: Journal of Chemical Physics. - : AIP. - 0021-9606 .- 1089-7690. ; 121:8, s. 3936-3938
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Tidskriftsartikel (refereegranskat)abstract
- Thermal conductivity measurements show that ice continues to amorphize for several days when kept at a fixed pressure p in the 0.79–0.88 GPa range, and fixed temperature T in the 127–130 K range. Thermal conductivity k decreases according to a stretched exponential in time, and its limiting long time value k() varies with p and T. At 0.8 GPa and 128 K, k() remains 2.5 times the value observed for high-density amorph. Consequences of these findings for our understanding of amorphization are discussed.
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| 9. |
- Broström, Markus, et al.
(författare)
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IACM - In situ alkali chloride monitor
- 2004
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Ingår i: 2nd World Conference for Energy, Industry and Climate Protection, Rome, Italy.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 10. |
- Eriksson, Lars-Ove, et al.
(författare)
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Myter och sanningar om svensk fiskodling
- 2003
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Ingår i: Torskar torsken? Forskare och fiskare om fisk och fiske. - Stockholm : Formas. ; , s. 103-111
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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