| 1. |
- Amirjani, M. R., et al.
(författare)
-
Protochlorophyllide and POR development in dark-grown plants with different proportions of short-wave length and long-wavelength protochlorophyllide spectral forms
- 2006
-
Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 128:4, s. 751-762
-
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.
|
|
| 2. |
- Abdelkader, Amal F., 1969, et al.
(författare)
-
Chlorophyll accumulation, protochlorophyllide formation and prolamellar body conversion are held back in wheat leaves exposed to high salt stress
- 2008
-
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
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
|
|
| 3. |
- Abdelkader, Amal F., 1969, et al.
(författare)
-
High salt stress in wheat leaves causes retardation of chlorophyll accumulation due to a limited rate of protochlorophyllide formation
- 2007
-
Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 130:1, s. 157-166
-
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.
|
|
| 4. |
- Abdelkader, Amal F., 1969, et al.
(författare)
-
High salt stress induces swollen prothylakoids in dark-grown wheat and alters both prolamellar body transformation and reformation after irradiation
- 2007
-
Ingår i: Journal of Experimental Botany. - : Oxford University Press (OUP). - 0022-0957 .- 1460-2431. ; 58:10, s. 2553-2564
-
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.
|
|
| 5. |
- Abdelkader, Amal F., 1969, et al.
(författare)
-
Prolonged salt stress alters the ratios of protochlorophyllide spectral forms in dark-grown wheat (Triticum aestivum) and influences chlorophyll a accumulation following irradiation
- 2010
-
Ingår i: ACTA PHYSIOLOGIAE PLANTARUM. - : Springer Science and Business Media LLC. - 0137-5881 .- 1861-1664. ; 32:5, s. 971-978
-
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.
|
|
| 6. |
- Amirjani, M.R., et al.
(författare)
-
Red region excitation spectra of protochlorophyllide in dark-grown leaves from plant species with different proportions of its spectral forms
- 2005
-
Ingår i: Photosynthetica. - : Institute of Experimental Botany. - 0300-3604 .- 1573-9058. ; 44:1, s. 83-92
-
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.
|
|
| 7. |
- Amirjani, M. R., et al.
(författare)
-
Regeneration of protochlorophyllide in green and greening leaves of plants with varying proportions of protochlorophyllide forms in darkness
- 2004
-
Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 121:3, s. 377-390
-
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.
|
|
| 8. |
- Aronsson, Henrik, et al.
(författare)
-
Characterisation of the assembly pathway of the pea NADPH:protochlorophyllide (Pchlide) oxidoreductase (POR), with emphasis on the role of its substrate, Pchlide
- 2001
-
Ingår i: Physiologia Plantarum. - Hoboken, NJ : Wiley-Blackwell Publishing Inc.. - 0031-9317 .- 1399-3054. ; 111:2, s. 239-244
-
Tidskriftsartikel (refereegranskat)abstract
- The homologous import and membrane association of a key enzyme for chlorophyll biosynthesis, the NADPH:protochlorophyllide (Pchlide) oxidoreductase (PAR, EC 1.6.99.1) into pea chloroplasts was investigated in vitro. The co-factor, NADPH, decreased binding of the precursor protein (pPOR) to the envelope membranes in the presence of ATP. The decrease of the binding reaction with NADPH was not observed with the precursor of the small subunit of Rubisco (pSS). To investigate possible substrate-dependency for the import reaction, internal Pchlide concentrations in the plastids were raised by either an addition of ÎŽ-aminolevulinic acid to isolated plastids or etiolation of the seedlings prior to plastid isolation. Increased amounts of plastid-bound Pchlide gave no observable differences in POR import. The capacity of POR and 11 different POR mutants, carrying charged-to-alanine scanning substitutions, to form a catalytically active POR-Pchlide-NADPH complex and to associate with the thylakoid membranes in a protease-resistant way were tested. Wild-type POR, as well as the mutants with charge substitutions in the N-terminal region of the protein, exhibited higher catalytic activity than the POR mutants carrying substitutions in the C-terminal region. Formation of a catalytically active complex did not, however, increase the association efficiency onto the thylakoids. We can, therefore, postulate that the import of pea POR into pea chloroplasts was not substrate-dependent, nor did formation of catalytically active complexes stimulate or inhibit the membrane association reaction of POR.
|
|
| 9. |
- Aronsson, Henrik, 1971, et al.
(författare)
-
Monogalactosyldiacylglycerol deficiency in Arabidopsis affects pigment composition in the prolamellar body and impairs thylakoid membrane energization and photoprotection in leaves
- 2008
-
Ingår i: Plant Physiology. - : Oxford University Press (OUP). - 0032-0889 .- 1532-2548. ; 148:1, s. 580-592
-
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.
|
|
| 10. |
- Aronsson, Henrik, et al.
(författare)
-
POR hits the road : import and assembly of a plastid protein
- 2003
-
Ingår i: Plant Molecular Biology. - Berlin : Springer-Verlag. - 0167-4412 .- 1573-5028. ; 51:1, s. 1-7
-
Tidskriftsartikel (refereegranskat)abstract
- The biosynthesis of chlorophyll is a strictly light-dependent multistep process in higher plants. The light-dependent step is catalysed by NADPH:protochlorophyllide oxidoreductase (POR, EC.1.6.99.1), which reduces protochlorophyllide (Pchlide) to chlorophyllide (Chlide). POR is nucleus-encoded and post-translationally imported into plastids. It has been proposed that the import of a POR protein isozyme (PORA) is totally dependent on Pchlide and uses a novel import pathway. This proposal is based on findings that PORA import only occurs in the presence of Pchlide and that the presence of overexpressed precursor of Rubisco small subunit (pSS), a protein which is known to use the general import pathway, does not outcompete PORA import. Another study demonstrated that POR precursor protein (pPOR) can be cross-linked to one of the components in the translocation machinery, Toc75, in the absence of Pchlide, and that its import can be outcompeted by the addition of the pSS. This indicates that pSS and pPOR may use the same translocation mechanism. Thus, POR does not necessarily need Pchlide for import – which is in contrast to earlier observations – and the exact POR import mechanism remains unresolved. Once in the stroma, the POR transit peptide is cleaved off and the mature POR protein is associated to the plastid inner membranes. Formation of the correct membrane–associated, thermolysin-protected assembly is strictly dependent of NADPH. As a final step, the formation of the NADPH-Pchlide-POR complex occurs. When POR accumulates in the membranes of proplastids, an attraction of monogalactosyl diacylglycerol (MGDG) can occur, leading to the formation of prolamellar bodies (PLBs) and the development of etioplasts in darkness.
|
|
