| 1. |
- Demmig-Adams, Barbara, et al.
(författare)
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Modulation of PsbS and flexible vs sustained energy dissipation by light environment in different species
- 2006
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 127, s. 670-80
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Tidskriftsartikel (refereegranskat)abstract
- Contrasting acclimation strategies of photosynthesis and photoprotection were identified for annual mesophytes (spinach, pumpkin, and Arabidopsis) vs the tropical evergreen Monstera deliciosa. The annual species utilized full sunlight for photosynthesis to a much greater extent than the evergreen species. Conversely, the evergreen species exhibited a greater capacity for photoprotective thermal energy dissipation as well as a greater expression of the PsbS protein in full sun than the annual species. In all species, the majority of thermal energy dissipation [assessed as non-photochemical fluorescence quenching (NPQ)] was the flexible, ΔpH-dependent form of NPQ over the entire range of growth light environments. However, in response to a transfer of shade-grown plants to high light, the evergreen species exhibited a high level of sustained thermal dissipation (qI), but the annual species did not. This sustained energy dissipation in the evergreen species was not ΔpH-dependent nor did the low level of PsbS in shade leaves increase upon transfer to high light for several days. Sustained ΔpH-independent NPQ was correlated (a) initially, with sustained D1 protein phosphorylation and xanthophyll cycle arrest and (b) subsequently, with an accumulation over several days of PsbS-related one-helix proteins and newly synthesized zeaxanthin and lutein.
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| 2. |
- Björn, G S, et al.
(författare)
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Action spectra for conversions of phycochrome c from Nostoc-muscorum
- 1978
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 43:3, s. 195-200
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Tidskriftsartikel (refereegranskat)abstract
- The reversibly photochromic pigment, phycochrome c, was extracted from the blue-green alga Nostoc muscorum strain A. Action spectra were determined for in vitro conversions of the pigment from the short wavelength to the long wavelength form and vice versa. The action peak for the absorbance decrease at 650 nm is at 630 nm. During this decrease there is only a slight increase of the absorbance in the green region. Green and yellow light (maximum efficiency at 580 nm) completely restores absorbance at 650 nm. The observations are explained by the existence of three spectrally different forms of phycochrome c: Pc630 and Pc650 which equilibrate in darkness and Pc580 which is reversibly photoconvertible to Pc630. We have also measured the absorbance changes brought about by saturating irradiations with light of various wavelengths ("photostationary state spectrum"). Extreme photostationary states were obtained with about 650 nm and 500 nm light.
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| 3. |
- Björn, G S, et al.
(författare)
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Light-induced, dark-reversible color shifts in petals of Phlox
- 1985
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 64:4, s. 445-448
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Tidskriftsartikel (refereegranskat)abstract
- Flowers of some Phlox (Phlox x paniculata L.) varieties undergo daily colour shifts, being blue in the early morning, turning red during the day, and returning to blue in the evening. The colour shift, which occurs only in the upper (adaxial) petal surfaces, is due to the daily changes in ambient light. In the laboratory, colour shifts could be induced by 2.5 h of ultraviolet, visible or far-red light and recorded by reflectance spectrophotometry. There are indications that irradiations with different kinds of light cause qualitatively different colour shifts, and that thus more than one photoreceptor pigment and more than one primary light reaction may be involved. The presence of phytochrome was demonstrated in petals of white Phlox flowers by in vivo transmission spectrophotometry. It is therefore possible that colour shifts in coloured Phlox flowers are mediated by phytochrome. Possibly the movement of ions (e.g. hydrogen ions) into or out of the vacuole (where the visible pigments are located) is affected by light absorption in a pigment in the tonoplast.
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| 4. |
- Björn, G S, et al.
(författare)
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Photochromic pigments from blue-green algae - phycochrome-A, phycochrome-B and phycochrome-C
- 1976
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 36:4, s. 297-304
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Tidskriftsartikel (refereegranskat)abstract
- Aqueous extracts of blue-green algae were fractionated by electrofocusing. In all algae investigated, fractions with isoelectric points at or near 4.6 showed photochromic behavior analogous to that of phytochrome, although they were sensitive to light of shorter wavelength. Three main types of photochromic pigments were found. Phycochrome a (in Tolypothrix distorta, Phormidium luridium, Nostoc muscorum 1453/12 and Anacystis nidulans) had 1 form absorbing maximally at about 590 nm (formed under red light) and 1 absorbing maximally at about 630 nm (formed under green light). Phycochrome b (in T. distorta) had 1 form absorbing maximally near 510 nm and 1 form absorbing maximally at 570 nm (formed in yellow-green and blue-green light, respectively). Phycochrome c (in N. muscorum A and probably in T. tenuis) had 1 form absorbing maximally at 650 nm (formed under green light) and 1 absorbing very weakly in the green region (formed under red light). The conversion of Phormidium phycochrome a from its red-absorbing form to its green-absorbing form caused the same spectral change as if an f-chromophore of phycocyanin were transformed into an s-chromophore. The quantum yield for this conversion was estimated to be 0.1, while the quantum yield for the reversion was estimated to be 0.4 on the assumption that the absorption coefficients were those of f- and s-chromophores. Phycochrome c was less light-sensitive than phycochromes a and b.
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| 5. |
- Björn, G S, et al.
(författare)
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Photochromic pigments in akinetes and pigment characteristics of akinetes in comparison with vegetative cells of Anabaena-Variabilis
- 1983
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 59:3, s. 493-500
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Tidskriftsartikel (refereegranskat)abstract
- Since akinete germination is triggered by light and the action spectrum for this process has features in common with the spectra of the two photochromic pigments, phycochromes b and d, a search was made for the presence of these phycochromes in akinetes of the blue-green alga. Anabaena variabilis Kützing. Allophycocyanin-B was also looked for, since the action spectrum for akinete germination points to a possible participation of this pigment too. Isoelectric focusing was used for purification of the pigments. The different fractions were investigated for phycochromes b and d by measuring the absorbance difference spectra: for phycochrome b. 500 nm irradiated minus 570 nm irradiated, and for phycochrome d, 650 nm irradiated minus 610 nm irradiated. For determination of allophycocyanin-B. fourth derivative analysis of absorption spectra was made for some of the fractions from the isoelectric focusing column. Phycochrome b was also assayed for by measuring in vivo absorption difference spectra. The assays were positive for all three pigments. The complete photosynthetic pigment systems were also studied by in vivo fluorescence measurements on both akinetes and vegetative cells of Anabaena variabilis. Fluorescence emission and excitation spectra at selected emission wavelengths were measured at room temperature and liquid nitrogen temperature. The energy transfer from phycoerythrocyanin to phycocyanin is very efficient under all conditions, as is the energy transfer from phycocyanin to allophycocyanin at room temperature. At low temperature, however, phycocyanin is partly decoupled from allophycocyanin, particularly in the akinetes; the energy transfer from allophycocyanin to chlorophyll a is less efficient at low temperature in both types of cells, but especially in akinetes. Delayed light emission was measured for both types of cells and found to be very weak in akinetes compared to vegetative cells. From this study it would seem that akinetes lack an active photosystem II, although the 691 nm peak in the 570 nm excited low temperature fluorescence emission spectrum proves the presence of photosystem II chlorophyll, and also its energetic connection to the phycobilisomes.
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| 6. |
- Björn, Lars Olof, et al.
(författare)
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Imaging by delayed light-emission (phytoluminography) as a method for detecting damage to the photosynthetic system
- 1979
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 47:4, s. 215-222
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Tidskriftsartikel (refereegranskat)abstract
- An improved apparatus for obtaining luminescence (delayed light emission) images of plants is described. It consists of a phosphoroscope equipped with an imaging lens and an electronic image intensifier. It is also equipped with light-sources for obtaining images with reflected light and fluorescence light. Damage to the photosynthetic system caused by virus, insects, high or low temperature, UV radiation, or herbicide, and also chloroplast senescence as part of a normal developmental process, can be followed by this non-destructive method. In many cases changes which are not visible in fluorescence images are clearly seen in luminescence images. (Leaves of Hibiscus sp., Oxalis tetraphylla, Nicotiana glutinosa with a tobacco mosaic virus infection, Fagus sylvatica with midge gall and Polypodium vulgare were used.).
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| 7. |
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| 8. |
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| 9. |
- Brodelius, M, et al.
(författare)
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Immunolocalization of the saposin-like insert of plant aspartic proteinases exhibiting saposin C activity. Expression in young flower tissues and in barley seeds
- 2005
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 125:4, s. 405-418
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Tidskriftsartikel (refereegranskat)abstract
- The plant- specific insert ( PSI) of cypro11 gene- encoding cyprosin, an aspartic proteinase from Cynara cardunculus, has been cloned by polymerase chain reaction ( PCR) into a bacterial expression vector. A rearranged form of this PSI in which the N- and C- terminal sequences were permutated to make it more similar to the structural arrangement observed in saposins was also cloned and expressed in the same system. The biological activities of the two purified recombinant proteins were compared to those of human saposins B and C. The proteins showed similar activity to saposin C, i. e. capacity to activate human glucosylceramidase. At a concentration of 5 mu M, wild- type PSI, saposin C, and rearranged PSI activated human glucosylceramidase two-, three-, and five- fold, respectively. The K-m for 4- methylumbelliferyl beta-glucopyranoside was around 7 mM in the presence of any of the three activators ( 5 mM). The neurotropic activity using NS20Y cells and lipid- binding properties of the plant recombinant proteins were tested. The two plant proteins showed lipid- binding properties similar to those of saposins but did not have any effect on neurite outgrowth. Immunolocalization of PSI showed its expression in protective tissues in flower meristem - protodermis, in C. cardunculus and embryonic root cap and coleorhiza in mature barley grains - as well as husk, pericarp, and the aleurone layer. Possible biological functions suggested for the plant homologue to saposins besides the general activation of enzymes involved in lipid metabolism would be involvement in plant defence.
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| 10. |
- Christensen, Anna, et al.
(författare)
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Overexpression of the Ca2+-binding protein calreticulin in the endoplasmic reticulum improves growth of tobacco cell suspensions (Nicotiana tabacum) in high-Ca2+ medium
- 2005
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 123:1, s. 92-99
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Tidskriftsartikel (refereegranskat)abstract
- Calreticulin (CRT) is a eukaryotic, highly conserved, Ca2+-binding protein predominantly located in the endoplasmic reticulum (ER) lumen. In addition to being involved in the regulation of cellular Ca2+, calreticulin is a key quality control element during protein folding in the ER lumen. Tobacco (Nicotiana tabacum L.) suspension cells overexpressing a maize CRT (CRT1a) were used here to examine the properties of CRT in growing plant cells with respect to stress exposure. The endogenous CRT gene was induced rapidly after subculturing of the cells to new medium. In accordance, the CRT protein levels increased, peaking at days 3-4. At day 5, when the CRT transcript levels had levelled off, a further increase in endogenous CRT expression was obtained when the cells were treated with excess Ca2+ or the N-linked glycosylation inhibitor tunicamycin. Whereas the response to Ca2+ occurred within 30 min, the induction by tunicamycin took several hours to be established. Transforming tobacco cells with maize CRT1a, under a constitutive mannopine synthase promoter, resulted in a stable level of expressed CRT1a during the growth cycle compared with endogenous CRT. The CRTs showed differences in attached glycans, but both contained the high mannose-rich-type glycans characteristic of ER proteins. In agreement with an ER location, both tobacco CRT and the transgene product CRT1a codistributed with the ER marker NADH cytochrome c reductase after density gradient centrifugation of microsomal fractions from tobacco cells. Increased production of CRT, as was obtained in the transgenic tobacco cell lines, made cells more tolerant than wild-type cells to high Ca2+ during growth. These data suggest that overexpression of CRT1a in plant cells results in a more efficient calcium buffering capacity in the ER.
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| 11. |
- Ekelund, Nils, 1956-, et al.
(författare)
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Photophobic stop-response in a dinoflagellate - modulation by preirridation
- 1987
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 70:3, s. 394-398
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Tidskriftsartikel (refereegranskat)abstract
- Gyrodinium dorsum Kofoid responds photophobically to flashes of blue light. The photophobic response consists of a cessation of movement (stop-response). Without background light and after a flash fluence above 10 J m-2, 75-85% of the cells show a stop-response, only only 50% of the cells show this response at 5 J m-2. With a flash fluence of 5 J m-2, background light of different wavelengths either increases (614 nm, 5.5-18.2 .mu.mol m-2 s-1) or decreases (700 nm, 18.4-36.0 .mu.mol m-2 s-1) the stop-response. Two hypotheses for the mechanism of the modulation by background light of the photophobic response are discussed: an effect of light on the balance of the photosynthetic system (PS I/PS II) or an effect on a phytochrome-like pigment (Pr /Pfr). This study supports the idea that a phytochrome-like pigment works in combination with a blue light-absorbing pigment. It was also found that cells of Gyrodinium dorsum cultured in red light (39.8 .mu.mol m-2) had a higher absorption in the red region of the absorption spectra than those cultured in white light (92.7 .mu.mol m-2).
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| 12. |
- Eskling, Marie, et al.
(författare)
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The xanthophyll cycle, its regulation and components
- 1997
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 100:4, s. 806-816
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Forskningsöversikt (refereegranskat)abstract
- During the last few years much interest has been focused on the photoprotective role of zeaxanthin. In excessive light zeaxanthin is rapidly formed in the xanthophyll cycle from violaxanthin, via the intermediate antheraxanthin, a reaction reversed in the dark. The role of zeaxanthin and the xanthophyll cycle in photoprotection, is based on fluorescence quenching measurements, and in many studies a good correlation to the amount of zeaxanthin (and antheraxanthin) has been found. Other suggested roles for the xanthophylls involve, protection against oxidative stress of lipids, participation in the blue light response, modulation of the membrane fluidity and regulation of abscisic acid synthesis. The enzyme violaxanthin de-epoxidase has recently been purified from spinach and lettuce as a 43-kDa protein. It was found as 1 molecule per 20-100 electron-transport chains. The gene has been cloned and sequenced from Lactuca sativa, Nicotiana tabacum and Arabidopsis thaliana. The transit peptide was characteristic of nuclear-encoded and lumen-localized proteins. The activity of violaxanthin de-epoxidase is controlled by the lumen pH. Thus, below pH 6.6 the enzyme binds to the thylakoid membrane. In addition ascorbate becomes protonated to ascorbic acid (pKa= 4.2) the true substrate (Km= 0.1 mM) for the violaxanthin de-epoxidase. We present arguments for an ascorbate transporter in the thylakoid membrane. The enzyme zeaxanthin epoxidase requires FAD as a cofactor and appears to use ferredoxin rather than NADPH as a reductant. The zeaxanthin epoxidase has not been isolated but the gene has been sequenced and a functional protein of 72.5 kDa has been expressed. The xanthophyll cycle pigments are almost evenly distributed in the thylakoid membrane and at least part of the pigments appears to be free in the lipid matrix where we conclude that the conversion by violaxanthin de-epoxidase occurs.
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| 13. |
- Forsberg, Jens, et al.
(författare)
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Protease activities in the chloroplast capable of cleaving an LHCII N-terminal peptide
- 2005
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 123:1, s. 21-29
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Tidskriftsartikel (refereegranskat)abstract
- Two protease activities of pea chloroplasts, one located in the stroma and the other associated to the thylakoid membrane, are described. Both proteases catalyse the endo-proteolytic cleavage of a peptide corresponding to the N-terminal loop and the first turn in helix-B of light-harvesting complex II (Lhcb1 from pea). The stromal protease cleaves preferentially on the carboxy-side of glutamic acid residues. Inhibitor studies indicate that this protease is a serine-type protease. The protease was partially purified and could be correlated to a 95-kDa polypeptide band on SDS-polyacrylamide gels. The 95 kDa protein was partially sequenced and showed similarity to an to an 'unknown protein' from A. thaliana (in the NCBI public database) as well as to a glutamyl endopeptidase purified from crude extract of cucumber leaves. It is concluded that the stromal protease is a chloroplast glutamyl endopeptidase (cGEP). The protease localized in the thylakoid membrane, cleaved the peptide at only one site, close to its N terminus. The activity of the thylakoid-associated protease was found to be drastically increased in the presence of the reducing agent 1,4-dithiothreitol. Inhibitor studies suggest that this protease is a cysteine- or serine-type protease. The possible roles of these proteases in the regulation of photosynthetic electron transport and in the chloroplast homeostasis are discussed.
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| 14. |
- Fredrikson, Karin, et al.
(författare)
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Isolation and polypeptide composition of 1,3-ß-glucan synthase from plasma membranes of Brassica oleracea
- 1991
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 81:3, s. 289-294
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Tidskriftsartikel (refereegranskat)abstract
- The l,3‐ß‐glucan synthase (callose synthase, EC 2.4.1.34) was solubilized from cauliflower (Brassica oleracea L.) plasma membranes with digitonin, and partially purified by ion exchange chromatography and gel filtration [fast protein liquid chromatography (FPLC)] using 3‐[(cholamidopropyl)dimethylammonio]‐1‐propane‐sulfonate (CHAPS) in the elution buffers. These initial steps were necessary to obtain specific precipitation of the enzyme during product entrapment, the final purification step. Five polypeptides of 32, 35, 57, 65 and 66 kDa were highly enriched in the final preparation and are thus likely components of the callose synthase complex. The purified enzyme was activated by Ca2+, spermine and cellobiose in the same way as the enzyme in situ, indicating that no essential subunits were missing. The polyglucan produced by the purified enzyme contained mainly 1,3‐linked glucose.
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| 15. |
- Gisselsson, A, et al.
(författare)
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Role of histidines in the binding of violaxanthin de-epoxidase to the thylakoid membrane as studied by site-directed mutagenesis
- 2004
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 122:3, s. 337-343
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Tidskriftsartikel (refereegranskat)abstract
- Regulation of violaxanthin de-epoxidase (VDE) involves a conformational change at low lumenal pH, followed by binding of the enzyme to the thylakoid membrane. The role of histidine residues in this process was studied by release of unbound enzyme from thylakoids upon sonication, on a pH scale from 4.7 to 7.1. The co-operativity for binding of spinach VDE (four histidines) to the membrane was found to be 3.8, with respect to protons, and had an inflexion point at pH 6.6, whereas VDE from wheat (three histidines) showed a co-operativity of 2.9 and had an inflexion point at pH 6.2. Mutant forms of VDE were constructed and probed for their binding to the outside of thylakoid membranes. With one or two histidines substituted for alanine or arginine, a lower co-operativity (1.6-2.3) was found, compared with the wild type. Based on these findings, and that the pKa value for histidine is within the range where the VDE binding takes place, we propose that protonation of the histidine residues at low pH induces the conformational change of VDE, and hence indirectly regulates binding of the enzyme to the thylakoid membrane.
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| 16. |
- Hideg, Éva, et al.
(författare)
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Ultraweak light emission, free radicals, chilling and light sensitivity
- 1996
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 98:2, s. 223-228
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Tidskriftsartikel (refereegranskat)abstract
- Ultraweak light emission (UWLE) was measured from leaves of various chillingsensitive (Lycopersicon esculentum, Cucumis sativus and Phaseolus vulgaris) and tolerant (Pisum sativum and Vicia faba) plants after exposure to low (47C) temperature in the light. UWLE increased upon chilling treatment combined with illumination with 200 mol m2 s1 PAR in all plants, by about 30 in tolerant and by more than 100 in sensitive plants. It increased more when applied together with 400 mol m2 s1 PAR: by 90100 and by 250280 in chillingtolerant and sensitive plants, respectively. Free radical production was detected by spintrapping EPR spectroscopy in thylakoid membranes isolated from the chillingtreated Lycopersicon esculentum and Vicia faba leaves. After 12 h chilling at 200 mol m2 s1 PAR, free radical production was approximately 3 times greater in the former than in the latter species. The same ratio was approximately 6 if chilling was carried out at 400 mol m2 s1 PAR, indicating the role of photooxidative stress in chilling injury.Our results also confirm that the stressinduced increase in UWLE is an indicator of free radical production and offers the possibility of using UWLE for monitoring the effect of chilling on temperaturesensitive plants in an early stage.
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| 17. |
- Hsiao, K C, et al.
(författare)
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Aspects of photoinduction of carotenogenesis in the fungus Verticillium-Agricinum
- 1982
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 54:3, s. 235-238
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Tidskriftsartikel (refereegranskat)abstract
- An action spectrum for light induced carotenogenesis in V. agaricinum (Link) Corda (ATCC 24668) was obtained by exposing mycelial pads to monochromatic radiation. Action maxima occurred at 290 (main peak) and 390 nm and there was a minor peak at 483 nm. An interaction between the blue and UV light occurred. Blue light partly reversed the UV light induction of carotenogenesis when given after, but not when given before UV light. This implies that there are at least 2 photoreceptors involved in carotenogenesis in Verticillium, but phytochrome is not likely to be one of them.
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| 18. |
- Hsiao, K C, et al.
(författare)
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Light-induced absorbance changes in the fungus Verticillium-Agricinum
- 1982
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 55:2, s. 73-75
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Tidskriftsartikel (refereegranskat)abstract
- Light-induced absorbance changes were investigated in vivo in the fungus V. agaricinum (Link) Corda. There was a broad light-induced absorbance decrease in the blue and near UV with a maximum at 384 nm. An action spectrum indicated that the absorbance changes were due to photo-bleaching of a pigment with an absorption spectrum that was similar to the action spectrum. Neither redox reactions nor energy metabolism were involved in the photo-bleaching process. A direct comparison of action spectra for light-induced absorbance changes and photo-induction of carotenogenesis suggests that the photo-bleaching may not be related to photo-induction of carotenogenesis.
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| 19. |
- Kjell, Jonas, et al.
(författare)
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Protein complexes of the plant plasma membrane resolved by Blue Native PAGE
- 2004
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 121:4, s. 546-555
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Tidskriftsartikel (refereegranskat)abstract
- With the characterization of the total genomes of Arabidopsis thaliana and Oryza sativa, several putative plasma membrane components have been identified. However, a lack of knowledge at the protein level, especially for hydrophobic proteins, have hampered analyses of physiological changes. To address whether protein complexes may be present in the native membrane, we subjected plasma membranes isolated from Spinacia oleracea leaves to blue-native polyacrylamide gel electrophoresis (BN-PAGE). BN-PAGE is well established in the separation of functional membrane protein complexes from mitochondria and chloroplasts, but a resolved protein complex pattern from PM of eukaryotic cells has previously not been reported. Using this method, protein complexes from Spinacia oleracea PM could be efficiently solubilized and separated, including the highly hydrophobic aquaporin (apparent molecular mass 230 kDa), a putative tetramer of H+-ATPase, and several less abundant complexes with apparent masses around or above 750 kDa. After denaturation and separation of the complexes into their subunits in a second dimension (SDS-PAGE), several of the complexes were identified as hydrophobic membrane proteins. Large amounts of protein (up to 1 mg) can be resolved in each lane, which suggests that the method could be used to study also low-abundance protein complexes, e.g. under different physiological conditions.
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| 20. |
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| 21. |
- Kumagai, T, et al.
(författare)
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Light-induced linear dichroism in photoreversibly photocromic sensor pigments 6. Relation between the 2 pigments of the mycochrome system in Alternaria-Chichorii
- 1984
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 60:4, s. 449-452
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Tidskriftsartikel (refereegranskat)abstract
- Conidiation in A. cichorii Nattras is reversibly stimulated by near UV radiation (NUV .apprx. 313 nm) and inhibited by blue light (.apprx. 450 nm) and apparently is a mycochrome-mediated process. After induction with plane-polarized NUV, blue light polarized perpendicularly to the NUV was more effective in counteracting the induction than was blue light polarized parallel to the NUV. Both the blue-absorbing component (presumably a flavo-protein) and the PNUV (NUV absorbing moiety) of the mycochrome system are membrane-bound. The transition moment associated with blue light absorption in the presumed flavoprotein forms an angle of at least 53.degree. with the transition moment associated with NUV absorption in PNUV.
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| 22. |
- Negash, L, et al.
(författare)
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Effect of ultraviolet-radiation and leakage of RB-86+ in guard-cells of Vicia-Faba
- 1987
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 69:2, s. 200-204
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Tidskriftsartikel (refereegranskat)abstract
- The effects of UV-C (254 nm), UV-A (365 nm) and broad-band UV (280-380 nm) on guard cells of Vicia faba L. cv. Long Pod were investigated in the presence of white light (450 .mu.mol m-2 s-1). UV-C (7 .mu.mol m-2 s-1) was found to cause leakage of 86Rb+ from guard cells, while UV-A (0.3 .mu.mol m-2 s-1) stimulated increased uptake in these cells. A relatively small stimulatory effect was observed by broad-band UV (3 .mu.mol m-2 s-1) during the first 30 min of irradiation with an apparent equilibration of influx and efflux thereafter. Leakage of 86Rb+ from guard cells continued despite the removal of UV-C and an increase in the amount of white light from 450 to 1500 .mu.mol m-2 s-1, suggesting that membranes were irreversibly damaged. Irradiation of guard cells UV-C for 30, 45 and 90 min indicated that these cells began to be affected already by 30 min UV-C irradiation.
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| 23. |
- Negash, L, et al.
(författare)
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Stomatal closure by ultraviolet-radiation
- 1986
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 66:3, s. 360-364
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Tidskriftsartikel (refereegranskat)abstract
- The effect of ultraviolet radiation (UV) (255-325 nm) on stomatal closure was investigated on tef (Eragrostis tef (Zucc) Trotter) in the presence of white light (ca 50 .mu.mol m-2 s-1). The action spectrum showed that UV (ca 2 .mu.mol m-2 s-1, half band width about 10 nm) of 285 nm or shorter wavelengths was very efficient in causing stomatal closure. The effectiveness decreased sharply towards longer wavelengths. Radiation of 313 nm or longer wavelengths was practically without effect. Increasing UV intensity increased stomatal resistance. When stronger white light (5 to 9 times stronger than the one used during irradiation) was administered stomates re-opened rapidly irrespective of whether the UV was on or off, although a subsequent gradual closing tendency was observed when the UV was on.
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| 24. |
- Panagopoulos, Ioannis, et al.
(författare)
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Response of sugar beet plants to ultraviolet-B (280-320 nm) radiation and Cercospora leaf spot disease
- 1992
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 84:1, s. 140-145
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Tidskriftsartikel (refereegranskat)abstract
- Sugar beet (Beta vulgaris L.) plants injected with Cercospora beticola Sacc. as well as non-infected plants were grown under visible light with or without ultraviolet-B (UV-B, 280-320 nm) radiation for 40 days. An interaction between UV-B radiation and Cercospora leaf spot disease was observed, resulting in a large reduction in leaf chlorophyll content, dry weight of leaf laminae, petioles and storage roots. Lipid peroxidation in leaves also increased the most under the combined treatments. This was also true for ultraweak luminescence from both adaxial and abaxial leaf surfaces. However, no correlation between lipid peroxidation and ultraweak luminescence was observed. Ultraviolet-B radiation given alone appeared to have either a stimulating effect, giving an increase in dry weight of laminae and reducing lipid peroxidation, or no effect. This lack of effect was seen in the absence of change in dry weight of storage roots and chlorophyll content relative to controls. The study demonstrated a harmful interaction between UV-B radiation and Cercospora leaf spot disease on sugar beet.
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| 25. |
- Panagopoulos, Ioannis, et al.
(författare)
-
The effect of UV-B and UV-C radiation on hibiscus leaves determined by ultraweak luminescence and fluorecence induction
- 1989
-
Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 76:4, s. 461-465
-
Tidskriftsartikel (refereegranskat)abstract
- The effects of UV-C (254 nm) and UV-B (280-320 nm) on chlorophyll fluorescence induction and ultraweak luminescence (UL) in detached leaves of Hibiscus rosa-sinensis L. were investigated. UL from leaves exposed to UV-B and UV-C radiation reached a maximum 72 h after irradiation. In both cases most of the light was of a wavelength over 600 nm. An increase in the percentage of long wavelength light with time was detected. UV radiation increased peroxidase activity, which also reached a maximum 72 h after irradiation. UV-B and UV-C both reduced variable chlorophyll fluorescence. No effect on the amount of chlorophyll or UV screening pigments was observed with the short-term irradiation used in this investigation.
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| 26. |
- Rasmusson, Allan, et al.
(författare)
-
Alternative oxidase: a defence against metabolic fluctuations?
- 2009
-
Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 137, s. 371-382
-
Tidskriftsartikel (refereegranskat)abstract
- An increasing number of oscillating or fluctuating cellular systems have been recently described following the adaptation of fluorescent technology. In diverse organisms, these variously involve signalling factors, heat production, central metabolism and reactive oxygen species (ROS). In response to many plant stresses and primarily via the influence of ROS, changes in mRNA and protein levels or in vivo activity of alternative oxidase are often observed. However, in several investigations, a lack of correlation between the mRNA, protein and in vivo activity has been evident. This discrepancy has made it questionable whether the induction of alternative oxidase has importance in regulating alternative pathway activity in vivo, or being diagnostic for a role of alternative oxidase in stress tolerance and ROS avoidance. Here, we suggest a role of alternative oxidase in counteracting deleterious short-term metabolic fluctuations, especially under stress conditions. This model emphasizes the importance of peak activity for establishing protein levels and allows an amalgamation of the present status of physiological, cellular and molecular knowledge.
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| 27. |
- Rasmusson, A. G., et al.
(författare)
-
Isolation of the rotenome-sensitive NADH-ubiquinone reductase (complex I) from red beet mitochondria
- 1994
-
Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 90:3, s. 607-615
-
Tidskriftsartikel (refereegranskat)abstract
- Complex 1 of the respirator) chain (EC 1.6.531, measured as NADH-duroquinone and NADH-ubiquinone, reductase activities, was isolated from purified red beetroot (Beta vulgaris L.I mitochondria. The mitochondria were disrupted by freeze-thawing and inner membrane vesicles were pelleted. After solubilization of the vesicles with Triton X-100, the enzyme complex was purified 11-fold (compared to the activity in the inner membrane vesicles) by size-exclusion chromatography on a Sephacryl S-400 HR column and then by ion-exchange chromatography on a DEAE-Sepharose CL-6B column. Triton X-100 was present throughout the purification procedure. Tire purified complex showed approximately 30 bands on SDS-PAGE and about 15 polypeptides including those at 80. 54, 53. 51. 27. 25 and 22 kDa cross-reacted with polyclonal antibodies raised against complex I from Neurospora crassa. This is similar lo the pattern obtained with complex I from Neurospera crassa.Analysis by nativc-SDS 2-dimensional PAGE revealed the existence of several molecular mass forms of the purified complex.After reconstitution of the purified complex into phosphatidylcholine vesicles, the NADH-ubiquinone reductase activity had a Km (NADH) of about I μM and was inhibited by both rotenone and dicyclohexylcarbodiimide.
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| 28. |
- Rasmusson, Allan, et al.
(författare)
-
Light and diurnal regulation of plant respiratory gene expression.
- 2007
-
Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 129:1, s. 57-67
-
Forskningsöversikt (refereegranskat)abstract
- Light is both the energy source and the dominant signalling input for photosynthetic organisms. Accordingly, up to 30–50% of the genes expressed in plant leaves are directly or indirectly regulated by light, and virtually all aspects of plant metabolism support photosynthesis, depend upon the products of photosynthesis or are affected by photosynthesis-related changes in metabolite levels. Though not directly tied to photosynthesis per se, mitochondria support several light-associated processes, including photorespiration, nitrogen metabolism, reductant transport and the maintenance of redox balance. Recently, it has become increasingly apparent that diverse light signalling pathways intersect with the mitochondrion, and that cellular respiration and photosynthesis display tight functional and regulatory coordination. In addition, global transcript analyses performed on plants exposed to different light qualities and intensities have started to provide promising starting points for the next series of investigations of light/diurnal regulation of respiratory metabolism.
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| 29. |
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| 30. |
- Struglics, André, et al.
(författare)
-
The presence of a short redox chain in the membrane of intact potato tuber peroxisomes and the association of malate dehydrogenase with the peroxisomal membrane
- 1993
-
Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 88:1, s. 19-28
-
Tidskriftsartikel (refereegranskat)abstract
- Peroxisomes and mitochondria were purified from potato tubers (Solanum tuberosum L. cv. Bintje) by differential centrifugation followed by separation on a continuous Percoll gradient containing 0.3 M sucrose in the lower half and 0.3 M mannitol in the upper half. The peroxisomes band at the bottom and the mitochondria in the middle of this type of gradient. Mitochondrial contamination of the peroxisomes was only 2% [as judged by cytochrome c oxidase (EC 1.3.9.1) activity]. Contamination by amyloplasts, plasma membrane and endoplasmic reticulum was also minimal. The peroxisomes were 80% intact as judged by malate dehydrogenase (MDH, NAD−-dependent; EC 1.1.1.37) latency.The specific activity of NADH-ferricyanide reductase and NADH-Cyt c reductase was 0.22 and 0.051 μmol (mg protein)−1 min−1 in freshly isolated peroxisomes, respectively. The active site of the reductase appeared to be on the inner surface of the membrane. The peroxisomes also contained a b-type cytochrome. Frozen peroxisomes were subfractionated by osmotic rupture followed by centrifugation to separate the soluble proteins from the peroxisomal membrane. About half the MDH and 30% of the NADH-ferricyanide reductase activity was associated with the membrane but only 6% of the catalase (EC 1.11.1.6) activity. A further wash removed 75% of the residual catalase with only a small loss of MDH or NADH-ferricyanide reductase activity. MDH appears to be closely associated with the peroxisomal membrane.When the purified peroxisomal membrane was analyzed by SDS-PAGE followed by silver staining, prominent bands at 22, 40, 41, 48, 53 and 74 kDa were observed. After immunoblotting the purified peroxisomal membrane, a band at 53 kDa showed strong cross-reactivity with antibodies raised against NADH-ferricyanide reductase. Since the NADH-ferricyanide reductase activity in the peroxisomal membrane could be shown to be specific for the β-hydrogen of NADH, the activity could not be due to contamination by endoplasmic reticulum where the reductase is α-specific. We conclude that the peroxisomal membrane contains a short redox chain, consisting of a NADH-ferricyanide reductase and a b-type cytochrome, similar to that of e.g. the plasma membrane. The role of this redox chain has yet to be elucidated.
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| 31. |
- Sundbom, E, et al.
(författare)
-
Phytoluminography - imaging plants by delayed light-emission
- 1977
-
Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 40:1, s. 39-41
-
Tidskriftsartikel (refereegranskat)abstract
- It is demonstrated that photographic images of plants can be produced in the absence of external illumination using an image intensifier. The image is produced by the weak delayed light emission (afterglow) from photosynthetically active chloroplasts. The use of such phytoluminographs is proposed for the study and diagnosis at an early stage of disturbances due to parasites, mineral deficiency, herbicides, frost, etc.
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| 32. |
- Sundqvist, C, et al.
(författare)
-
Light-induced linear dichroism in photoreversibly photochromic sensor pigments 3. Chromophore rotation estimated by polarized-light reversal of dichroism
- 1983
-
Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 59:2, s. 263-269
-
Tidskriftsartikel (refereegranskat)abstract
- Phytochrome from oats (Avena sativa L. cv. Sol II), partially purified on brushite, was immobilized on Sepharose beads to which antiphytochrome immunoglobulin had been covalently linked. The immobilized phytochrome was first brought to the Pr form with unpolarized far-red light. The change in linear dichroism at 660 nm induced by plane polarized red light, and its reversal by plane polarized far-red light were then studied using a dual-wavelength spectrophotometer equipped with polarizing filters. The far-red light was most effective in reversing red-induced dichroism when the angle between the planes of polarization of red and far-red light was approximately 23.degree.. From this it was computed that the long-wavelength transition moment of phytochrome rotates about 29.degree. (or 180-29.degree.) with respect to the protein during conversion from Pr to Pfr. The reverse experiment, using unpolarized red light followed first by polarized far-red light and then polarized red light, with dichroism monitored at 730 nm, also gives most effective reversal for an angle of about 23.degree. between polarization planes, but this corresponds to a transition moment rotation of about 36.degree. (or 180.degree.-36.degree.). The present method is more straightforward but less accurate and confirms an earlier conclusion that the rotation angle is close to 32.degree. (or 180.degree.-32.degree.) in contrast to the "in vivo" value of 90.degree. found by several workers.
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| 33. |
- Vogelmann, T C, et al.
(författare)
-
Measurement of light gradients and spectral regime in plant-tissue with a fiber optic probe
- 1984
-
Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 60:3, s. 361-368
-
Tidskriftsartikel (refereegranskat)abstract
- A method is described in which light gradients and spectral regime can be measured within plant tissue using fiber optics. A fiber optic probe was made by modifying a single optical fiber (200 μm diameter) so that it had a light harvesting end that was a truncated tip 20–70 μm in diameter. The probe was a directional sensor with a half-band acceptance angle of 17–20°. Light measurements were made as the fiber optic probe was driven through plant tissue by a motorized micromanipulator, and the light that entered the fiber tip was piped to a spectroradiometer. By irradiating green leaf tissue of the succulent Crassula falcata L. with collimated light and inserting the probe from different directions, it was possible to measure light quality and quantity at different depths. Collimated light was scattered completely by the initial 1.0 mm of leaf tissue, which also greatly attenuated all light except the green and far-red. Light scatter contributed significantly to light quantity and had a pronounced spectral structure. Immediately beneath the irradiated surface the amount of light at 550 nm was 1.2 times that of the incident light. The light gradient declined rapidly to 0.5 times incident light at 1.4 mm depth. In contrast, the amount of light at 750 nm increased during the initial 0.5 mm to 2.9 times incident light and then declined linearly to 0.5 times incident light at the dark side of the leaf (4.5 mm). The implications of the magnitude of the contribution of light scatter to the light gradient is also discussed.
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| 34. |
- Vogelmann, T C, et al.
(författare)
-
Plants as light traps
- 1986
-
Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 68:4, s. 704-708
-
Tidskriftsartikel (refereegranskat)
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| 35. |
- Vogelmann, T C, et al.
(författare)
-
Response to directional light by leaves of a sun-tracking lupine (Lupinus Succulentus)
- 1983
-
Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 59:4, s. 533-538
-
Tidskriftsartikel (refereegranskat)abstract
- Experiments were done to examine the phototrophic response of sun-tracking leaves of Lupinus succulentus Dougl. to fixed beams of white and broad band light. Upon irradiation with 15 W m-2 white light that struck the laminae at an angle of 45°, there was a 45–60 min lag period prior to leaf movement. The greatest rate of movement was 15° h-1, and reorientation ceased when leaves attained a position within 15° of perpendicular to the light beam. Laminar movement was largely pulvinar, and a 60 min inductive light treatment was sufficient to activate a maximum pulvinar response in subsequent darkness. Light striking the lamina at angles between 20 and 70° induced similar maximum pulvinar responses and only light that struck the upper (adaxial) leaf surface was effective. Leaf tracking was fully activated by blue light but not by red or yellow light.
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| 36. |
- Widell, Susanne, et al.
(författare)
-
Light-induced absorption changes in etiolated Coleoptiles
- 1976
-
Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 36:4, s. 305-309
-
Tidskriftsartikel (refereegranskat)abstract
- Blue (or green) light induced reversible and irreversible absorption changes in etiolated wheat (Triticum aestivum) coleoptiles. Immediately after a 10 s pulse of blue light, there was an absorbance increase at 440 nm and a decrease at 420 nm. The absorbance at 440 nm returned to the original level in a biphasic way with 1st-order rate constants of 0.05 s-1 and 0.006 s-1 at 25.degree. C. The change at 440 nm was partly, but not completely, inhibited by iodide. In the 500-600 nm region, complex changes occurred, indicating the participation of at least 2 different cytochromes, one of which was oxidized during a 10 s light pulse and the other oxidized more slowly during the following dark period.
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| 37. |
- Guy, Charles, et al.
(författare)
-
Plant cold and abiotic stress gets hot
- 2006
-
Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 126, s. 1-4
-
Tidskriftsartikel (refereegranskat)
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| 38. |
- Sirrenberg, Anke, et al.
(författare)
-
Piriformospora indica affects plant growth by auxin production
- 2007
-
Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 131, s. 581–589-
-
Tidskriftsartikel (populärvet., debatt m.m.)abstract
- Piriformospora indica has been shown to improve the growth of many plant species including Arabidopsis thaliana, but the mechanism by which this is achieved is still unclear. Arabidopsis root colonization by P. indica was examined in sterile culture on the medium of Murashige and Skoog. P. indica formed intracellular structures in Arabidopsis root epidermal cells and caused changes in root growth, leading to stunted and highly branched root systems. This effect was because of a diffusible factor and could be mimicked by IAA. In addition, P. indica was shown to produce IAA in liquid culture. We suggest that auxin production affecting root growth is responsible for, or at least contributes to, the beneficial effect of P. indica on its host plants.
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| 39. |
- 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.
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| 40. |
- 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.
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| 41. |
- 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.
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| 42. |
- 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.
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| 43. |
- Aronsson, Henrik, et al.
(författare)
-
POR – import and membrane association of a key element in chloroplast development
- 2003
-
Ingår i: Physiologia Plantarum. - : Blackwell Publishing. - 0031-9317 .- 1399-3054. ; 118:1, s. 1-9
-
Tidskriftsartikel (refereegranskat)abstract
- The development of proplastids or etioplasts to chloroplast is visualized by the accumulation of chlorophyll in leaves of higher plants. The biosynthesis of chlorophyll includes a light-dependent reduction of protochlorophyllide (Pchlide) to chlorophyllide (Chlide). This light-dependent step is catalysed by the nucleus-encoded NADPH:Pchlide oxidoreductase (POR, EC 1.6.99.1). POR is active within plastids and therefore has to be translocated over the plastid envelope membranes. The import of chloroplast proteins seems to follow a general import pathway using translocons at the outer and inner envelope membrane. POR cross-linking to Toc75, one of the major translocon components at the outer envelope membrane, indicates its use of the general import pathway. However, since variations exist within the so-called general import pathway one has to consider previous data suggesting a novel totally Pchlide-dependent import pathway of one POR isoform, PORA. The suggested Pchlide dependency of POR import is discussed since recent observations contradict this idea. In the stroma the POR transit peptide is cleaved off and the mature POR protein is targeted to the plastid inner membranes. The correct and stable association of POR to the membrane requires the cofactor NADPH. Functional activity of POR calls for formation of an NADPH–Pchlide–POR complex, a formation that probably takes place after the membrane association and is dependent on a phosphorylation reaction.
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| 44. |
- Askerlund, Per, et al.
(författare)
-
Cytochromes of plant plasma membranes : Characterization by absorbance difference spectrophotometry and redox titration
- 1989
-
Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 76:2, s. 123-134
-
Tidskriftsartikel (refereegranskat)abstract
- The cytochrome composition of plasma membranes (PM) obtained by phase partitioning of microsomal fractions from spinach leaves (Spinacea oleracea L. cv. Medania), cauliflower inflorescences (Brassica oleracea L.), sugar beer leaves (Beta vulgaris L.) and barley (Hordeum vulgare L. cv. Kristina) roots and leaves was characterized by absorbance difference spectrophotometry at different reducing conditions at 20 and – 196°C, by redox titration, and by heme staining of polypeptide bands after lithium dodecyl sulfate polyacrylamide gel electrophoresis (LDS-PAGE). The location of the α-bands in the difference spectra and the loss of heme after treatment with LDS indicated that predominantly cytochromes of the b-type were present in all species tested. The total concentration of cytochrome was ca 0.35 nmol (mg protein)−1. The main component (ca 70% of total) was completely reduced by ascorbate and partly by NADH and had a midpoint potential of ca 150 mV. At – 196°C, ascorbate reduction revealed a symmetrical α-band at ca 557 nm with PM from spinach leaves, cauliflower and sugar beet leaves, but with barley root and leaf PM ascorbate reduction resulted in an asymmetrical α-band (shoulder at 552, maximum at 559 nm). In the dithionite-reduced minus ascorbate-reduced spectrum at –196°C a split α-band (552 + 558 nm) was seen with PM from all species. This minor component had a midpoint potential of ca – 50 mV and is probably identical to cytochrome b5, the presence of which would explain the relatively high NADH-cytochrome c reductase activities observed with plant PM. With PM from cauliflower, CO-difference spectra indicated that cytochromes P-420 and P-450 were present at concentrations up to 0.06 and 0.03 nmol (mg protein)−1, respectively. Visualization of cytochromes by heme staining after LDS-PAGE was complicated by endogenous peroxidase activity and by loss of heme during solubilisation. A presumptive b-cytochrome (heme-stained band at 94 kDa) was only detected with barley leaf PM.
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| 45. |
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| 46. |
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| 47. |
|
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| 48. |
- Björn, Gunvor S, et al.
(författare)
-
Light-induced lineardichroism in photoreversibly photochromic sensor pigments - IV. Lack of chromophore rotation in phycochrome b immobilized in vitro.
- 1984
-
Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 60, s. 253-256
-
Tidskriftsartikel (refereegranskat)abstract
- In photochromic pigments, immobilized on Sepharose beads to prevent reorientation of the molecules, linear absorption dichroism can be induced with plane‐polarized light. This phenomenon was used to study the relation between the carrier protein and the chromophore in the photochromic cyanobacterial pigment, phycochrome b, from Tolypothrix distorta var. symplocoides Hansgirg, strain UTEX 424 (formerly IUCC 424). It was found that the transition moment of the chromophore has the same direction with respect to the protein in the long‐wavelength and the short‐wavelength forms of phycochrome b. This contrasts to earlier results for phytochrome in higher plants, in which the transition moment was found to rotate 32° (or 180°—32°) when the long‐wavelength form was converted to the short‐wavelength form or vice versa.
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| 49. |
- Brosché, Mikael, et al.
(författare)
-
Molecular events following perception of ultraviolet-B radiation by plants
- 2003
-
Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 117:1, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- Exposure of plants to UV-B radiation (280–320 nm) results in changes in expression of a large number of genes. Before UV-B radiation or light of other wavelengths can give rise to a cellular response, it has to be perceived by some kind of receptor, and the information transduced via a signalling pathway to the target molecules, be it proteins in the cytoplasm or the genetic material in the nucleus. The perception of low levels of UV-B probably occurs via a UV-B photoreceptor followed by several different signalling pathways. These pathways include second messengers such as calcium, kinases and the catalytic formation of reactive oxygen species. High levels of UV-B, on the other hand, probably cause cellular damage and oxidative stress, thus activating a general stress signal transduction pathway which leads to a response similar to that which occurs after pathogen attack and other stresses. Some of the genes identified so far as being regulated by UV-B encode proteins involved in the biosynthesis of protective pigments, DNA repair and antioxidative enzymes, photosynthetic genes, cell cycle genes, and stress genes induced by other types of stimuli (i.e. pathogenesis-related proteins and senescence-induced genes). In the light of the information obtained on components necessary for UV-B-induced changes in gene expression, we propose in this mini-review a working model for UV-B perception and signal transduction. This model also takes into account dosage differences for the observations, which imply a separation into UV-B-specific and more general stress signal transduction.
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