| 1. |
- Amirjani, M. R., et al.
(författare)
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Protochlorophyllide and POR development in dark-grown plants with different proportions of short-wave length and long-wavelength protochlorophyllide spectral forms
- 2006
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 128:4, s. 751-762
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Tidskriftsartikel (refereegranskat)abstract
- The effect of leaf developmental age on the protochlorophyllide (Pchlide) spectral forms and the expression of messenger RNA (mRNA) encoding NADPH-protochlorophyllide oxidoreductase (POR) were investigated. Four plant species, maize, wheat, pea and the lip 1 mutant of pea, known to have different composition of the spectral forms of Pchlide, were used. In very young plants short-wavelength Pchlide with a fluorescence emission at 631 nm was dominating. Long-wavelength Pchlide fluorescing mainly around 655 nm increased during development, which led to a relative decrease of the short-wavelength forms. During ageing of the leaves, the short-wavelength forms slightly increased again. The different proportions of short- and long-wavelength Pchlide spectral forms were, however, found to vary with the developmental stage in a species specific pattern. The steady-state level of POR mRNA and the amount of the POR protein were similar in species dominated by short-wavelength forms and in species dominated with long-wavelength forms. Even if POR is necessary for the formation of the long-wavelength Pchlide form it is not the only limiting factor for formation of long-wavelength Pchlide forms in mature plants.
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| 2. |
- Abdelkader, Amal F., 1969, et al.
(författare)
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Chlorophyll accumulation, protochlorophyllide formation and prolamellar body conversion are held back in wheat leaves exposed to high salt stress
- 2008
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Ingår i: In: Allen JF, Gantt E, Golbeck JH, Osmond B (eds.) Proceedings of the 14th International Congress on Photosynthesis, Glasgow, Scotland, July 22-27 2007. ; , s. 1139-1142
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 3. |
- Abdelkader, Amal F., 1969, et al.
(författare)
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High salt stress in wheat leaves causes retardation of chlorophyll accumulation due to a limited rate of protochlorophyllide formation
- 2007
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 130:1, s. 157-166
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Tidskriftsartikel (refereegranskat)abstract
- When exposed to salt stress, leaves from dark-grown wheat seedlings (Triticum aestivum, cv. Giza 168) showed reduced accumulation of chlorophyll during irradiation. To elucidate the mechanism behind salt-influenced reduction of chlorophyll biosynthesis, we have investigated the effect of salt stress on the spectral forms of Pchlide, the phototransformation of Pchlide to Chlide, the Shibata shift, the regeneration of Pchlide and the accumulation of Pchlide from 5-aminolevulinic acid (ALA). We found that the phototransformation of Pchlide to Chlide was not affected by salt stress. The blue shift (Shibata shift) of newly formed Chlide was delayed both after flash irradiation and in continuous light. The reformation of Pchlide in darkness after a flash irradiation or after a period of 3-h irradiation was retarded in the salt-treated leaves. However, after a 20-h dark period, Pchlide was reformed even in salt-treated leaves but the formation of short-wavelength Pchlide was suppressed. Compared to controls, salt treatment also reduced the amount of Pchlide accumulated in leaves floated on ALA. The increase in the low temperature fluorescence emission spectrum at 735 nm, which occurred gradually during several hours of irradiation with continuous light in control leaves, was completely suppressed in salt-treated leaves. It is concluded that salt stress inhibits chlorophyll accumulation partly by reducing the rate of porphyrin formation but, as discussed, also by a possible reduction in the formation of chlorophyll-binding proteins.
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| 4. |
- Abdelkader, Amal F., 1969, et al.
(författare)
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High salt stress induces swollen prothylakoids in dark-grown wheat and alters both prolamellar body transformation and reformation after irradiation
- 2007
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Ingår i: Journal of Experimental Botany. - : Oxford University Press (OUP). - 0022-0957 .- 1460-2431. ; 58:10, s. 2553-2564
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Tidskriftsartikel (refereegranskat)abstract
- High salinity causes ion imbalance and osmotic stress in plants. Leaf sections from 8-d-old dark-grown wheat (Triticum aestivum cv. Giza 168) were exposed to high salt stress (600 mM) and the native arrangements of plastid pigments together with the ultrastructure of the plastids were studied using low-temperature fluorescence spectroscopy and transmission electron microscopy. Although plastids from salt-treated leaves had highly swollen prothylakoids (PTs) the prolamellar bodies (PLBs) were regular. Accordingly, a slight intensity decrease of the short-wavelength protochlorophyllide (Pchlide) form was observed, but no change was found in the long-wavelength Pchlide form emitting at 656 nm. After irradiation, newly formed swollen thylakoids showed traversing stromal strands. The PLB dispersal was partly inhibited and remnants of the PLBs formed an electron-dense structure, which remained after prolonged (8 h) irradiation. The difference in fluorescence emission maximum of the main chlorophyll form in salt-stressed leaves (681 nm) and in control leaves (683 nm) indicated a restrained formation of the photosynthetic apparatus. Overall chlorophyll accumulation during prolonged irradiation was inhibited. Salt-stressed leaves returned to darkness after 3 h of irradiation had, compared with the control, a reduced amount of Pchlide and reduced reformation of regular net-like PLBs. Instead, the size of the electron-dense structures increased. This study reports, for the first time, the salt-induced swelling of PTs and reveals traversing stromal strands in newly formed thylakoids. Although the PLBs were intact and the Pchlide fluorescence emission spectra appeared normal after salt stress in darkness, plastid development to chloroplasts was highly restricted during irradiation.
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| 5. |
- Abdelkader, Amal F., 1969, et al.
(författare)
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Prolonged salt stress alters the ratios of protochlorophyllide spectral forms in dark-grown wheat (Triticum aestivum) and influences chlorophyll a accumulation following irradiation
- 2010
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Ingår i: ACTA PHYSIOLOGIAE PLANTARUM. - : Springer Science and Business Media LLC. - 0137-5881 .- 1861-1664. ; 32:5, s. 971-978
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Tidskriftsartikel (refereegranskat)abstract
- To examine the effects of salt stress on darkgrown wheat (Triticum aestivum), seedlings of the salt-tolerant cultivar Sids 1 and the susceptible cultivar Giza 168 were grown in darkness for 14 days in nutrient solution with and without 200 mM of supplementary salt (100 mM of NaCl and 100 mM of KCl). During this time, we monitored their protochlorophyllide (Pchlide) contents, ratios of photoactive to non-photoactive forms of Pchlide (from 655/633-nm emission ratios in their 77 K fluorescence emission spectra) and (following flash irradiation) ratios of newly formed chlorophyllide (Chlide) to non-photoactive Pchlide. In addition, the accumulation of chlorophyll a in leaf sections was monitored during prolonged (24 h) irradiation. The results depended on the developmental state of the seedlings. However, the salt stress treatment caused marked increases in both Pchlide contents in dark-grown leaves and in Chlide contents following irradiation of leaf sections of both cultivars. The ratio of phototransformable to non-phototransformable Pchlide and the abundance of newly formed Chlide were also increased by the salt stress. Further, leaves of salt-stressed seedlings consistently accumulated more chlorophyll a than leaves of unstressed seedlings when floating on the nutrient solution (with or without supplementary salt) in continuous white light. The findings are consistent with the hypothesis that increased levels of the long-wavelength form of Pchlide contribute to protective mechanisms against salt stress.
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| 6. |
- Amirjani, M.R., et al.
(författare)
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Red region excitation spectra of protochlorophyllide in dark-grown leaves from plant species with different proportions of its spectral forms
- 2005
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Ingår i: Photosynthetica. - : Institute of Experimental Botany. - 0300-3604 .- 1573-9058. ; 44:1, s. 83-92
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Tidskriftsartikel (refereegranskat)abstract
- Etiolated leaves of three different species, maize, wheat, and pea, as well as a pea mutant (lip1) were used to compare the excitation spectra of protochlorophyllide (Pchlide) in the red region. The species used have different composition of short-wavelength and long-wavelength Pchlide forms. The relation between different forms was furthermore changed through incubating the leaves in 5-aminolevulinic acid (ALA), which caused an accumulation of short-wavelength Pchlide forms, as shown by changes in absorption and fluorescence spectra. This is the first time a comprehensive comparison is made between excitation spectra from different species covering an emission wavelength range of 675750 nm using fluorescence equipment with electronic compensation for the variations in excitation irradiance. The different forms of Pchlide having excitations peaks at 628, 632, 637, 650, and 672 nm could be best measured at 675, 700, 710, 725, and 750 nm, respectively. Measuring emission at wavelengths between 675 710 nm gave an exaggeration of the short-wavelength forms and measuring at longer wavelengths gave for the pea leaves an exaggeration of the 672 nm peak. In general, an energy transfer from short-wavelength Pchlide forms to long-wavelength Pchlide forms occurred, but such an energy transfer sometimes seemed to be limited as a result of a discrete location of the Pchlide spectral forms. The excitation spectra resembling the absorption spectrum most were measured at an emission wavelength of 740 nm. Measuring the excitation at 710 nm gave higher intensity of the spectra but the short-wavelength forms were accentuated.
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| 7. |
- Amirjani, M. R., et al.
(författare)
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Regeneration of protochlorophyllide in green and greening leaves of plants with varying proportions of protochlorophyllide forms in darkness
- 2004
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 121:3, s. 377-390
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Tidskriftsartikel (refereegranskat)abstract
- During illumination of dark-grown plants protochlorophyllide (Pchlide) is continuously transformed to chlorophyllide (Chlide). Different dark-grown plants, maize (Zea mays cv. Sundance), wheat (Triticum aestivum cv. Kosack), pea (Pisum sativum cv. Kelwedon wonder), the lip1 mutant of pea, and the aurea mutant of tomato (Solanum lycopersicum), have various ratios of spectral Pchlide forms in darkness. When the plants were illuminated and then returned to darkness Pchlide re-accumulated. The proportions of different Pchlide forms within the pool of re-accumulated Pchlide were followed by low temperature fluorescence emission and excitation spectra in green and greening leaves. After 1 h of illumination the spectral characteristics of regenerated Pchlide forms mirrored those of Pchlide in dark-grown plants and were thus species dependent. After a prolonged illumination period (24 h) as well as in fully green leaves energy transfer to chlorophyll (Chl) masked the presence of long-wavelength Pchlide in the fluorescence emission spectra. However, excitation spectra showed Pchlide absorption around 650 nm and its flash-induced disappearance confirmed its nature of phototransformable Pchlide. In fact the excitation spectra showed that the proportions of different Pchlide forms in green leaves highly resembled the proportions of Pchlide forms in dark-grown leaves and were specific for the plant variety. Thus Chl formation in both dark-grown and light-grown leaves can occur in a similar way through the main photoactive long-wavelength form of Pchlide.
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| 8. |
- Aronsson, Henrik, 1971, et al.
(författare)
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Monogalactosyldiacylglycerol deficiency in Arabidopsis affects pigment composition in the prolamellar body and impairs thylakoid membrane energization and photoprotection in leaves
- 2008
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Ingår i: Plant Physiology. - : Oxford University Press (OUP). - 0032-0889 .- 1532-2548. ; 148:1, s. 580-592
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Tidskriftsartikel (refereegranskat)abstract
- Monogalactosyldiacylglycerol (MGDG) is the major lipid constituent of chloroplast membranes and has been proposed to act directly in several important plastidic processes, particularly during photosynthesis. In this study, the effect of MGDG deficiency, as observed in the monogalactosyldiacylglycerol synthase1-1 (mgd1-1) mutant, on chloroplast protein targeting, phototransformation of pigments, and photosynthetic light reactions was analyzed. The targeting of plastid proteins into or across the envelope, or into the thylakoid membrane, was not different from wild-type in the mgd1 mutant, suggesting that the residual amount of MGDG in mgd1 was sufficient to maintain functional targeting mechanisms. In dark-grown plants, the ratio of bound protochlorophyllide (Pchlide, F656) to free Pchlide (F631) was increased in mgd1 compared to the wild type. Increased levels of the photoconvertible pigment-protein complex (F656), which is photoprotective and suppresses photooxidative damage caused by an excess of free Pchlide, may be an adaptive response to the mgd1 mutation. Leaves of mgd1 suffered from a massively impaired capacity for thermal dissipation of excess light due to an inefficient operation of the xanthophyll cycle; the mutant contained less zeaxanthin and more violaxanthin than wild type after 60 min of high-light exposure and suffered from increased photosystem II photoinhibition. This is attributable to an increased conductivity of the thylakoid membrane at high light intensities, so that the proton motive force is reduced and the thylakoid lumen is less acidic than in wild type. Thus, the pH-dependent activation of the violaxanthin de-epoxidase and of the PsbS protein is impaired.
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| 9. |
- Blomqvist, Lisa A., 1978, et al.
(författare)
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Proteomic analysis of highly purified prolamellar bodies reveals their significance in chloroplast development
- 2008
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Ingår i: Photosynthesis Research. - : Springer Science and Business Media LLC. - 0166-8595 .- 1573-5079. ; 96:1, s. 37-50
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Tidskriftsartikel (refereegranskat)abstract
- The prolamellar body (PLB) proteome of dark-grown wheat leaves was characterized. PLBs are formed not only in etioplasts but also in chloroplasts in young developing leaves during the night, yet their function is not fully understood. Highly purified PLBs were prepared from 7-day-old dark-grown leaves and identified by their spectral properties as revealed by low-temperature fluorescence spectroscopy. The PLB preparation had no contamination of extra-plastidal proteins, and only two envelope proteins were found. The PLB proteome was analysed by a combination of 1-D SDS-PAGE and nano-LC FTICR MS. The identification of chlorophyll synthase in the PLB fraction is the first time this enzyme protein was found in extracts of dark-grown plants. This finding is in agreement with its previous localization to PLBs using activity studies. NADPH:protochlorophyllide oxidoreductase A (PORA), which catalyses the reduction of protochlorophyllide to chlorophyllide, dominates the proteome of PLBs. Besides the identification of the PORA protein, the PORB protein was identified for the first time in dark-grown wheat. Altogether 64 unique proteins, representing pigment biosynthesis, photosynthetic light reaction, Calvin cycle proteins, chaperones and protein synthesis, were identified. The in number of proteins' largest group was the one involved in photosynthetic light reactions. This fact strengthens the assumption that the PLB membranes are precursors to the thylakoids and used for the formation of the photosynthetic membranes during greening. The present work is important to enhance our understanding of the significance of PLBs in chloroplast development.
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| 10. |
- Blomqvist, Lisa A., 1978, et al.
(författare)
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Proteomic analysis of the etioplast inner membranes of wheat (Triticum aestivum) by two-dimensional electrophoresis and mass spectrometry
- 2006
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317. ; 128:2, s. 368-381
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Tidskriftsartikel (refereegranskat)abstract
- The proteome of the etioplast inner membranes (EPIM) of dark-grown wheat leaves (Triticum aestivum L.) was mapped as an essential part of studies on plastid differentiation. Proteins were separated by two-dimensional gel electrophoresis and analysed with mass spectrometry (MS). Over 200 protein spots were resolved and visualized by Coomassie blue staining. More than 100 spots were submitted for subsequent mass spectrometry analyses by matrix-assisted laser desorption ionizationtime of flight (MALDI-ToF) MS, electrospray tandem MS (ESI-MS/MS) or liquid chromatographymass spectrometry (LC-MS/MS). There were 46 identified spots, from which at least 21 different proteins were identified. Among these were FtsH proteases and the peptidyl-prolyl cistrans isomerase TLP40, as well as chloroplast coupling factor subunits and extrinsic subunits of photosystem II (PSII). Of special interest is the NADPH:protochlorophyllide oxidoreductase (POR), which is the predominant protein of prolamellar bodies, where it accumulates in a highly stable ternary complex with protochlorophyllide and NADPH. This complex is known to play an important role in the formation and dispersal of prolamellar bodies. Five different isoforms of POR, with different pI values, were identified. We discuss the possibility of these isoforms being differently phosphorylated as part of the regulation of PORpigment complexes. The proteome mapping of EPIM is a crucial step in the understanding of the light-dependent transition of etioplasts to chloroplasts, and provides a basis for functional studies on factors influencing the greening process.
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