| 1. |
- Kalbin, Georgi, et al.
(author)
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UV-B-induced DNA damage and expression of defence genes under UV-B stress : tissue-specific molecular marker analysis in leaves
- 2001
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In: Plant, Cell and Environment. - : Wiley. - 0140-7791 .- 1365-3040. ; 24:9, s. 983-990
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Journal article (peer-reviewed)abstract
- The aim of this study was to investigate the regulatory effect of ultraviolet-B (UV-B) radiation on a number of key stress response genes found in the epidermis and mesophyll of Pisum sativum L., Argenteum mutant. This mutant was chosen for the ease with which the entire epidermis can be removed from the mesophyll tissue. An additional goal was to explore the potential modifying effect of pre-acclimation of plants to UV-B radiation prior to exposure by UV-B during treatment. Results showed that mRNA accumulation was similar during acute short-term UV-B exposure for chalcone synthase (Chs) and short-chain alcohol dehydrogenase (SadA) in both epidermis and mesophyll. In contrast, the mRNA levels differed considerably between tissues for phenylalanine ammonia lyase, chalcone isomerase and lipid transfer protein. After 24 h incubation in visible light after cessation of UV-B exposure, the regulation of mRNA levels also differed between Chs and SadA, the former showing no expression in the epidermis and the latter none in the mesophyll. Acclimation to low UV-B levels before acute exposures resulted in delayed induction of Chs and SadA. Measurements of UV-B-induced cyclobutane pyrimidine dimers (CPDs) showed a greater formation in epidermis than in mesophyll. In addition, acclimation at low UV-B levels resulted in significantly higher basal levels of CPDs than in non-acclimated plants in both mesophyll and epidermis and also in increased damage in concomitant acute exposures. The lack of correlation between the number of CPDs and levels of transcripts for defence genes, indicates that DNA damage does not control transcription of these genes.
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| 2. |
- Noren, H., et al.
(author)
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Expression of the early light-induced protein but not the PsbS protein is influenced by low temperature and depends on the developmental stage of the plant in field-grown pea cultivars
- 2003
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In: Plant, Cell and Environment. - : Wiley. - 0140-7791 .- 1365-3040. ; 26:2, s. 245-253
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Journal article (peer-reviewed)abstract
- Plant cells exposed to photo-inhibitory conditions respond by accumulation of the early light-induced proteins (Elips) with a potential photoprotective function. Here we studied the expression of Elip in various pea cultivars grown under agricultural or climate-chamber conditions. We demonstrated that the expression of Elip in all cultivars was developmentally regulated and its level decreased during flowering and post-flowering periods. Surprisingly, significant amounts of Elip transcripts, but not proteins, accumulated in senescing leaves already under low light conditions and the exposure to light stress resulted in a 10-times higher induction of Elip transcripts. Furthermore, the expression pattern of Elip transcript and protein significantly differed under field and growth-chamber conditions. First, the expression level of Elip was much higher in field-grown than in chamber-grown cultivars. Second, substantial amounts of Elip transcripts and protein were detected during the night in field-grown plants in contrast to chamber-grown cultivars due to a synergistic effect of light stress occurring during the day and low temperature present during the following night. The expression of the PsbS protein related to Elips and involved in the photoprotection of the photosystem II was relatively constant under all conditions tested.
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| 3. |
- Moroney, J V, et al.
(author)
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Carbonic anhydrases in plants and algae
- 2001
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In: Plant, Cell and Environment. - 0140-7791 .- 1365-3040. ; 24:2, s. 141-153
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Research review (peer-reviewed)abstract
- Carbonic anhydrases catalyse the reversible hydration of CO2, increasing the interconversion between CO2 and HCO3- + H+ in living organisms. The three evolutionarily unrelated families of carbonic anhydrases are designated alpha-, beta -and gamma -CA. Animals have only the alpha -carbonic anhydrase type of carbonic anhydrase, but they contain multiple isoforms of this carbonic anhydrase. In contrast, higher plants, algae and cyanobacteria may contain members of all three CA families. Analysis of the Arabidopsis database reveals at least 14 genes potentially encoding carbonic anhydrases. The database also contains expressed sequence tags (ESTs) with homology to most of these genes. Clearly the number of carbonic anhydrases in plants is much greater than previously thought. Chlamydomonas, a unicellular green alga, is not far behind with five carbonic anhydrases already identified and another in the EST database. In algae, carbonic anhydrases have been found in the mitochondria, the chloroplast thylakoid, the cytoplasm and the periplasmic space. In C-3 dicots, only two carbonic anhydrases have been localized, one to the chloroplast stroma and one to the cytoplasm. A challenge for plant scientists is to identify the number, location and physiological roles of the carbonic anhydrases.
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| 4. |
- Savitch, L V, et al.
(author)
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Two different strategies for light utilization in photosynthesis in relation to growth and cold acclimation
- 2002
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In: Plant, Cell and Environment. - 0140-7791 .- 1365-3040. ; 25:6, s. 761-771
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Journal article (peer-reviewed)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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| 5. |
- Strand, Åsa, 1977-, et al.
(author)
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Altering flux through the sucrose biosynthesis pathway in transgenic Arabidopsis thaliana modifies photosynthetic acclimation at low temperatures and the development of freezing tolerance
- 2003
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In: Plant, Cell and Environment. - 0140-7791 .- 1365-3040. ; 26:4, s. 523-535
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Journal article (peer-reviewed)abstract
- To test the hypothesis that the up-regulation of sucrose biosynthesis during cold acclimation is essential for the development of freezing tolerance, the acclimation responses of wild-type (WT) Arabidopsis thaliana (Heynh.) were compared with transgenic plants over-expressing sucrose phosphate synthase (over-sps) or with antisense repression of either cytosolic fructose-1,6-bisphosphatase (antifbp) or sucrose phosphate synthase (antisps). Plants were grown at 23 degreesC and then shifted to 5 degreesC. The leaves shifted to 5 degreesC for 10 d and the new leaves that developed at 5 degreesC were compared with control leaves on plants at 23 degreesC. Plants over-expressing sucrose phosphate synthase showed improved photosynthesis and increased flux of fixed carbon into sucrose when shifted to 5 degreesC, whereas both antisense lines showed reduced flux into soluble sugars relative to WT. The improved photosynthetic performance by the over-sps plants shifted to 5 degreesC was associated with an increase in freezing tolerance relative to WT (-9.1 and -7.2 degreesC, respectively). In contrast, both antisense lines showed impaired development of freezing tolerance (- 5.2 and -5.8 degreesC for antifbp and antisps, respectively) when shifted to 5 degreesC. In the new leaves developed at 5 degreesC the recovery of photosynthesis as typically seen in WT was strongly inhibited in both antisense lines and this inhibition was associated with a further failure of both antisense lines to cold acclimate. Thus, functional sucrose biosynthesis at low temperature in the over-sps plants reduced the inhibition of photosynthesis, maintained the mobilization of carbohydrates from source leaves to sinks and increased the rate at which freezing tolerance developed. Modification of sucrose metabolism therefore represents an additional approach that will have benefits both for the development of freezing tolerance and over-wintering, and for the supply of exportable carbohydrate to support growth at low temperatures.
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| 6. |
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| 7. |
- Nordgren, A, et al.
(author)
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Tree root and soil heterotrophic respiration as revealed by girdling of boreal Scots pine forest: : extending observations beyond the first year
- 2003
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In: Plant, Cell and Environment. - : Wiley. - 0140-7791. ; 26:8, s. 1287-1296
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Journal article (peer-reviewed)abstract
- Limitations in available techniques to separate autotrophic (root) and soil heterotrophic respiration have hampered the understanding of forest C cycling. The former is here defined as respiration by roots, their associated mycorrhizal fungi and other micro-organisms in the rhizosphere directly dependent on labile C compounds leaked from roots. In order to separate the autotrophic and heterotrophic components of soil respiration, all Scots pine trees in 900 m2 plots were girdled to instantaneously terminate the supply of current photosynthates from the tree canopy to roots. Högberg et al. (Nature 411, 789-792, 2001) reported that autotrophic activity contributed up to 56% of total soil respiration during the first summer of this experiment. They also found that mobilization of stored starch (and likely also sugars) in roots after girdling caused an increased apparent heterotrophic respiration on girdled plots. Herein a transient increase in the δ13C of soil CO2 efflux after girdling, thought to be due to decomposition of 13C-enriched ectomycorrhizal mycelium and root starch and sugar reserves, is reported. In the second year after girdling, when starch reserves of girdled tree roots were exhausted, calculated root respiration increased up to 65% of total soil CO2 efflux. It is suggested that this estimate of its contribution to soil respiration is more precise than the previous based on one year of observation. Heterotrophic respiration declined in response to a 20-day-long 6 °C decline in soil temperature during the second summer, whereas root respiration did not decline. This did not support the idea that root respiration should be more sensitive to variations in soil temperature. It is suggested that above-ground photosynthetic activity and allocation patterns of recent photosynthates to roots should be considered in models of responses of forest C balances to global climate change
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| 8. |
- Takeuchi, A., et al.
(author)
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Changes in synthesis and degradation of Rubisco and LHCII with leaf age in rice (Oryza sativa L.) growing under supplementary UV-B radiation
- 2002
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In: Plant, Cell & Environment. - : Wiley. - 0140-7791. ; 25:6, s. 695-706
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Journal article (peer-reviewed)abstract
- The effects of supplementary ultraviolet-B (UV-B) radiation on the changes in synthesis and degradation of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and light-harvesting chlorophyll a/b binding protein of PSII (LHCII) were examined, as well as mRNA levels for small and large subunits of Rubisco (rbcS and rbcL, respectively) and LHCII (cab) with leaf age in UVsensitive rice (Norin 1) and UV-resistant rice (Sasanishiki). Both Rubisco and LHCII were actively synthesized until the leaf had fully expanded, and then decreased with increasing leaf age. Synthesis of Rubisco, but not LHCII, was significantly suppressed by UV-B in Norin 1. The degradation of Rubisco was enhanced by UV-B around the time of leaf maturation in the two cultivars. The levels of rbcS and rbcL were reduced by UV-B at the early stages after leaf emergence in both cultivars. Cab transcripts were first present at high levels in the two cultivars, but drastically decreased due to UV-B treatment immediately after leaf emergence in Norin 1. It was shown that synthesis and degradation of Rubisco and LHCII greatly changed with leaf age: Rubisco synthesis was significantly suppressed by supplementary UV-B radiation at the transcription step during the early leaf stages. It was also suggested that the difference in UV-B sensitivity in Rubisco synthesis between the two rice cultivars might be due to specific suppression both transcriptionally and post-transcriptionally.
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