| 1. |
- Ivanov, A. G., et al.
(författare)
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Implications of alternative electron sinks in increased resistance of PSII and PSI photochemistry to high light stress in cold-acclimated Arabidopsis thaliana
- 2012
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Ingår i: Photosynthesis Research. - Dordrecht : Springer Science and Business Media LLC. - 0166-8595 .- 1573-5079. ; 113:1-3, s. 191-206
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Tidskriftsartikel (refereegranskat)abstract
- Exposure of control (non-hardened) Arabidopsis leaves to high light stress at 5 A degrees C resulted in a decrease of both photosystem II (PSII) (45 %) and Photosystem I (PSI) (35 %) photochemical efficiencies compared to non-treated plants. In contrast, cold-acclimated (CA) leaves exhibited only 35 and 22 % decrease of PSII and PSI photochemistry, respectively, under the same conditions. This was accompanied by an accelerated rate of P700(+) re-reduction, indicating an up-regulation of PSI-dependent cyclic electron transport (CET). Interestingly, the expression of the NDH-H gene and the relative abundance of the Ndh-H polypeptide, representing the NDH-complex, decreased as a result of exposure to low temperatures. This indicates that the NDH-dependent CET pathway cannot be involved and the overall stimulation of CET in CA plants is due to up-regulation of the ferredoxin-plastoquinone reductase, antimycin A-sensitive CET pathway. The lower abundance of NDH complex also implies lower activity of the chlororespiratory pathway in CA plants, although the expression level and overall abundance of the other well-characterized component involved in chlororespiration, the plastid terminal oxidase (PTOX), was up-regulated at low temperatures. This suggests increased PTOX-mediated alternative electron flow to oxygen in plants exposed to low temperatures. Indeed, the estimated proportion of O-2-dependent linear electron transport not utilized in carbon assimilation and not directed to photorespiration was twofold higher in CA Arabidopsis. The possible involvement of alternative electron transport pathways in inducing greater resistance of both PSII and PSI to high light stress in CA plants is discussed.
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| 2. |
- Leonardos, E D, et al.
(författare)
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Daily photosynthetic and C-export patterns in winter wheat leaves during cold stress and acclimation
- 2003
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Ingår i: Physiologia Plantarum. - 0031-9317 .- 1399-3054. ; 117:4, s. 521-531
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Tidskriftsartikel (refereegranskat)abstract
- Diurnal patterns of whole-plant and leaf gas exchange and (14) C-export of winter wheat acclimated at 20 and 5degreesC were determined. The 5degreesC-acclimated plants had lower relative growth rates, smaller biomass and leaf area, but larger specific leaf weight than 20degreesC plants. Photosynthetic rates in 20degreesC and 5degreesC-acclimated leaves were similar; however, daytime export from 5degreesC-acclimated leaves was 45% lower. Photosynthesis and export remained steady in 20degreesC and 5degreesC-acclimated leaves during the daytime. By comparison, photosynthesis in 5degreesC-stressed leaves (20degreesC-acclimated plants exposed to 5degreesC 12 h before and during measurements) declined from 70 to 50% of the 20degreesC-acclimated leaves during the daytime, while export remained constant at 35% of the 20degreesC-acclimated and 60% of the 5degreesC-acclimated leaves. At high light and CO2 , photosynthesis and export increased in both 20degreesC and 5degreesC-acclimated leaves, but rates in 5degreesC-stressed leaves remained unchanged. At all conditions daytime export was greater than nighttime export. Taken together, during cold acclimation photosynthesis was upregulated, whereas export was only partially increased. We suggest that this reflects a requirement of cold-acclimated plants to both sustain an increased leaf metabolic demand while concomitantly supporting translocation of photoassimilates to overwintering sinks.
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| 3. |
- Pocock, T H, et al.
(författare)
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Susceptibility to low-temperature photoinhibition and the acquisition of freezing tolerance in winter and spring wheat : The role of growth temperature and irradiance
- 2001
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Ingår i: Physiologia Plantarum. - 0031-9317 .- 1399-3054. ; 113:4, s. 499-506
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Tidskriftsartikel (refereegranskat)abstract
- Five winter and five spring wheat (Triticum aestivum L.) cultivars were grown under either control conditions (20 degreesC/250 photosynthetic photon flux density (PPFD) [mu mol m(-2) s(-1)]), high irradiance (20 degreesC/800 PPFD) or at low temperature (either 5 degreesC/250 PPFD or 5 degreesC/50 PPFD). To eliminate any potential bias, the wheat cultivars were arbitrarily chosen without any previous knowledge of their freezing tolerance or photosynthetic competence. We show that the differential susceptibilities to photoinhibition exhibited between spring and winter wheat cultivars, as assessed by chlorophyll fluorescence cannot be explained on the basis of either growth irradiance or low growth temperature per se. The role of excitation pressure is discussed. We assessed the correlation between susceptibility to low-temperature photoinhibition, maximum ribulose 1,5-bisphosphate carboxylase-oxygenase (EC 4.1.1.39) and NADP-dependent malate dehydrogenase (EC 1.1.1.82) activities, chlorophyll and protein concentrations and freezing tolerance determined by electrolyte leakage. Susceptibility to photoinhibition is the only parameter examined that is strongly and negatively correlated with freezing tolerance. We suggest that the assessment of susceptibility to photoinhibition may be a useful predictor of freezing tolerance and field survival of cereals.
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| 4. |
- 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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| 5. |
- 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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