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  • 1
    Electronic Resource
    Electronic Resource
    Influence of cesium on tetrapyrrole biosynthesis in etiolated and greening barley leaves (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 99 (1997), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Cesium chloride (CsCl) treatment of greening primary leaves of barley for 8 h inhibited chlorophyl] accumulation in a concentration-dependent manner and led to the accumulation of excessive amounts of uroporphyrin(ogen) III (URO[gen]) and to a minor extent of heptacarboxylporphyrin(ogen). When dark-grown leaves were incubated with CsCl, accumulation of URO(gen) was observed only after feeding of the tetrapyrrole precursor 5-aminolevulinic acid. Western blot analysis showed no apparent difference in content of uroporphyrinogen decarboxylase (EC 4.1.1.37, UROD) or selected proteins involved in tetrapyrrole biosynthesis in extracts of CsCl-incubated (15 mM) versus control leaves. UROD activity was drastically decreased upon CsCl treatment in leaves incubated in the dark or in the light (44 and 86%, respectively). Selected preceding enzymes of the tetrapyrrole biosynthetic pathway, 5-aminolevulinic acid dehydratase (EC 4.2.1.24, ALAD) and porphobilinogen deaminase (EC 4.3.1.8, PBGD), were influenced only to a minor extent under standard incubation conditions (15 mM CsCl). Furthermore, the ALA synthesizing capacity did not differ in leaves incubated with and without Cs− cations. UROD activity of crude homogenates from control plants and after partial purification was reduced to 56 and 80%, respectively, upon addition of 10 mM CsCl. Equal concentrations of KCl were not inhibitory. Enzyme assays of the same barley extract in the presence of CsCl yielded no effect on ALAD and a minor loss of PBGD activity. The initial visible cytotoxic effect of CsCl appeared to be a selective inhibition of UROD resulting in accumulation of photosensitizing URO (gen). Consequences of the diminished UROD activity on early steps of the tetrapyrrole biosynthesis and its functional and regulatory significance for the porphyrin synthesis are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1997.tb03444.x
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  • 2
    Electronic Resource
    Electronic Resource
    Tobacco uroporphyrinogen-III decarboxylase: characterization, crystallization and preliminary X-ray analysis (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 1709-1711 
    Details
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Uroporphyrinogen-III decarboxylase from Nicotiana tabacum is a plastidial enzyme involved in the biosynthesis of chlorophyll and haem. Sedimentation equilibrium with protein producing diffracting crystals clearly indicates that the enzyme is a homodimer under similar ionic strength conditions to those found in the chloroplast stroma. Additionally, dynamic light scattering reveals an ionic strength dependence for this oligomerization state. Crystals were obtained in the hexagonal space group P622 with one molecule per asymmetric unit and diffracted to 2.3 Å resolution using synchrotron radiation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0907444901013361
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  • 3
    Electronic Resource
    Electronic Resource
    Cell wall synthesis in carrot cells: Comparison of suspension-cultured cells and regenerating protoplasts (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 79 (1990), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The synthesis of cell walls and extracellular material during the regeneration of carrot (Daucus carota L. ssp. sativus) protoplasts was examined. Cell walls and extracellular material were analysed for their carbohydrate content. In cell walls, the amount of carbohydrate increased 4- to 5-fold with only minor changes in neutral sugar composition. Glucose was abundant, during cultivation, making up to 70% (w/w) followed by mannose, which accounted for 17%. This indicates the formation of a glucomannan. The neutral sugar composition of extracellular polysaccharides showed greater variety with a signifiant increase of arabinose and galactose during cultivation. This feature is probably connected to the occurrence of arabinogalactan proteins in the culture medium. Hydroxyproline, an indicator for extensin and arabinogalactan proteins, showed an increase parallel to the formation of cell walls and extracellular polysaccharides. Results are compared with corresponding data from suspension-cultured cells used for protoplast isolation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1990.tb06752.x
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  • 4
    Electronic Resource
    Electronic Resource
    Purification and characterization of sinapoylglucose:malate sinapoyltransferase from Raphanus sativus L. (1992)
    Springer
    Planta 187 (1992), S. 236-241 
    Details
    ISSN: 1432-2048
    Keywords: Acyltransferase ; Glucose ester ; Hydroxycinnamic acid ; Phenylpropanoid metabolism ; Raphanus ; Sinapic acid ester ; l-Sinapoylglucose:malate sinapoyltransferase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract 1-O-Sinapoyl-β-glucose:l-malate O-sinapoyltransferase (SMT; EC 2.3.1.) from cotyledons of red radish (Raphanus sativus L. var. sativus) was purified to apparent homogeneity with a 2100-fold enrichment and a 4% recovery. Apparent Mrs of 52 and 51, respectively, were determined by gel filtration and by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). On isoelectric focusing, the SMT resolved into two isoforms which, on SDS-PAGE, showed, slightly different Mrs (SMT I: Mr/isoelectric point = 51/5.75; SMT II: Mr/isoelectric point = 51.5/5.9). The highest activity of SMT was found at pH 6.0 (50% at pH 5.5 and pH 6.5). The temperature maxima in the presence of 10, 50, 100 and 250 mM malate were 22, 30, 35 and 37° C, respectively, with energies of activation of 55, 81, 96 and 121 kJ · mol-1. The enzyme accepted all the hydroxycinnamic acid-glucose esters tested with relative ratios of initial velocity values of 100∶85∶45∶26∶2.6 of 1-O-sinapoyl-, 1-O-feruloyl-, 1-O-caffeoyl-, 1,2-di-O-sinapoyl-, and 1-O-(4-coumaroyl)-β-glucose. It showed an absolute acceptor specificity for l-malate. d-Malate as second acceptor molecule in standard assays with l-malate inhibited the reaction velocity noncompetitively (K i = 215 mM). The substrate saturation curves were not hyperbolic. The data for sinapoylglucose indicated substrate activation; those for l-malate, substrate inhibition. Kinetic analysis suggests a random bi bi mechanism within two ranges of substrate concentrations, with a kinetically preferred pathway via the enzyme-sinapoylglucose complex indicating a slow-transition mechanism. This may be interpreted as hysteretic cooperativity with sinapoylglucose.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00201945
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  • 5
    Electronic Resource
    Electronic Resource
    Expression studies in tetrapyrrole biosynthesis: inverse maxima of magnesium chelatase and ferrochelatase activity during cyclic photoperiods (1999)
    Springer
    Planta 208 (1999), S. 264-273 
    Details
    ISSN: 1432-2048
    Keywords: Key words: Chlorophyll ; Chloroplast ; Circadian rhythm ; Heme ; Nicotiana (tetrapyrroles) ; Pigment synthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. The synthesis of tetrapyrroles is regulated in anticipation of rhythmic changes in environmental conditions such as light intensity and temperature. To assess the control of the rate-limiting steps of the metabolic flow as well as the distribution of precursors for chlorophyll and heme synthesis, RNA steady-state levels and activities of enzymes involved in tetrapyrrole biosynthesis were analysed from 4-week-old tobacco (Nicotiana tobacum L.) plants grown under photoperiodically changing conditions. The kinetics of RNA levels and the enzyme activities were compared with those from plants which grew subsequent to the light/dark cycles for 48 h under constant light or dark conditions. The analysis revealed that the two peak activities for 5-aminolevulinic acid synthesis and of magnesium-protoporphyrin IX chelatase (Mg-chelatase) corresponded with the highest accumulation of the transcripts encoding glutamyl-tRNA reductase and CHL H, a subunit of Mg-chelatase, in the first half of the light period during a light/dark cycle. The activity of ferrochelatase (Fe-chelatase) and the level of its RNA showed a maximum just at the transition from light to dark and oscillated with a phase approximately opposite to that of Mg-chelatase activity. The control of 5-aminolevulinic acid synthesis and of the allocation of protoporphyrin IX to Mg- or Fe-chelatase probably reflect the functional coordination of tetrapyrrole biosynthesis in response to daily fluctuations in tetrapyrrole requirements. It is suggested that the coordination of expression and enzyme activities allows, in the light phase, an extensive flow of substrates into the chlorophyll-synthesizing branch of the metabolic pathway and, after the transition from light to dark, a channeling into the heme biosynthetic pathway. Implications for feedback control in the pathway are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050558
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  • 6
    Electronic Resource
    Electronic Resource
    Isolation, sequencing and expression of cDNA sequences encoding uroporphyrinogen decarboxylase from tobacco and barley (1995)
    Springer
    Plant molecular biology 28 (1995), S. 245-256 
    Details
    ISSN: 1573-5028
    Keywords: barley ; chlorophyll biosynthesis ; chloroplast ; expression ; haem biosynthesis ; hemE ; regulation ; tobacco ; uroporphyrinogen decarboxylase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We have cloned and sequenced a full-length cDNA for uroporphyrinogen decarboxylase (UROD, EC 4.1.1.37) from tobacco (Nicotiana tabacum L.) and a partial cDNA clone from barley (Hordeum vulgare L.). The cDNA of tobacco encodes a protein of 43 kDa, which has 33% overall similarity to UROD sequences determined from other organisms. We propose that tobacco UROD has an N-terminal extension of 39 amino acid residues. This extension is most likely a chloroplast transit sequence. The in vitro translation product of UROD was imported into pea chloroplasts and processed to ca. 39 kDa. A truncated cDNA, from which the putative transit peptide had been deleted, was used to over-express the mature UROD in Escherichia coli. Purified protein showed UROD activity, thus providing an adequate source for subsequent enzymatic characterization and inhibition studies. Expression of UROD was investigated by northern and western blot analysis during greening of etiolated barley seedlings, and in segments of barley primary leaves grown under day/night cycles. The amount of RNA and protein increased during illumination Maximum UROD-RNA levels were detected in the basal segments relative to the top of the leaf.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00020244
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  • 7
    Electronic Resource
    Electronic Resource
    Coproporphyrinogen III oxidase from barley and tobacco — sequence analysis and initial expression studies (1995)
    Springer
    Planta 196 (1995), S. 796-803 
    Details
    ISSN: 1432-2048
    Keywords: 5-Aminolevulinate synthesis ; Chlorophyll synthesis ; Chloroplast (development) ; Hordeum ; Nicotiana ; Tetrapyrrole
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Coproporphyrinogen III oxidase (coprogen oxidase; EC 1.3.3.3) is part of the pathway from 5-aminolevulinate to protoporphyrin IX which is common in all organisms and catalyses oxidative decarboxylation at two tetrapyrrole side chains. We cloned and sequenced fulllength cDNAs encoding coprogen oxidase from barley (Hordeum vulgare L.) and tobacco (Nicotiana tabacum L.). They code for precursor peptides of 43.6 kDa and 44.9 kDa, respectively. Import into pea plastids resulted in a processed tobacco protein of approx. 39 kDa, which accumulated in the stroma fraction. Induction of synthesis of recombinant putative tobacco mature coprogen oxidase consisting of 338 amino-acid residues in Escherichia coli at 20°C result in a catalytically active protein of approx. 39 kDa, while induction of its formation at 37°C immediately terminated bacterial growth, possibly due to toxic effects on the metabolic balance of tetrapyrrole biosynthesis. The plant coprogen oxidase gene was expressed to different extents in all tissues investigated. This is most likely due to the differing requirements for tetrapyrroles in different organs. The steady-state level of mRNA did not significantly differ in etiolated and greening barley leaves. The content of coprogen oxidase RNA reached its maximum in developing cells and decreased drastically when cells were completely differentiated. Functioning of the two photosystems apparatus requires the synthesis of all pigment and protein components during plant development. It is speculated that the enzymes involved in tetrapyrrole synthesis are developmentally rather than light-dependently regulated. Regulation of these enzymes also guarantees a constant flux of metabolic intermediates and avoids photodynamic damage by accumulating porphyrins.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00197347
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  • 8
    Electronic Resource
    Electronic Resource
    Coproporphyrinogen III oxidase from barley and tobacco — sequence analysis and initial expression studies (1995)
    Springer
    Planta 196 (1995), S. 796-803 
    Details
    ISSN: 1432-2048
    Keywords: 5-Aminolevulinate synthesis ; Chlorophyll synthesis ; Chloroplast (development) ; Hordeum ; Nicotiana ; Tetrapyrrole
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Coproporphyrinogen III oxidase (coprogen oxidase; EC 1.3.3.3) is part of the pathway from 5-aminolevulinate to protoporphyrin IX which is common in all organisms and catalyses oxidative decarboxylation at two tetrapyrrole side chains. We cloned and sequenced fulllength cDNAs encoding coprogen oxidase from barley (Hordeum vulgare L.) and tobacco (Nicotiana tabacum L.). They code for precursor peptides of 43.6 kDa and 44.9 kDa, respectively. Import into pea plastids resulted in a processed tobacco protein of approx. 39 kDa, which accumulated in the stroma fraction. Induction of synthesis of recombinant putative tobacco mature coprogen oxidase consisting of 338 amino-acid residues inEscherichia coli at 20°C result in a catalytically active protein of approx. 39 kDa, while induction of its formation at 37°C immediately terminated bacterial growth, possibly due to toxic effects on the metabolic balance of tetrapyrrole biosynthesis. The plant coprogen oxidase gene was expressed to different extents in all tissues investigated. This is most likely due to the differing requirements for tetrapyrroles in different organs. The steady-state level of mRNA did not significantly differ in etiolated and greening barley leaves. The content of coprogen oxidase RNA reached its maximum in developing cells and decreased drastically when cells were completely differentiated. Functioning of the two photosystems apparatus requires the synthesis of all pigment and protein components during plant development. It is speculated that the enzymes involved in tetrapyrrole synthesis are developmentally rather than light-dependently regulated. Regulation of these enzymes also guarantees a constant flux of metabolic intermediates and avoids photodynamic damage by accumulating porphyrins.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01106776
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  • 9
    Electronic Resource
    Electronic Resource
    Comparative analysis of the low molecular weight and enzymatic antioxidants in response to the phototoxicity of accumulating uroporphyrin and protochlorophyllide in barley leaves treated with cesium chloride (2000)
    Springer
    Photosynthesis research 64 (2000), S. 267-276 
    Details
    ISSN: 1573-5079
    Keywords: barley ; cesium cations ; Hordeum vulgare ; oxidative stress ; porphyrinogenesis ; tetrapyrrole
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Cesium chloride treatment of illuminated barley leaves leads to accumulation of uroporphyrinogen which is subsequently either oxidised to uroporphyrin in continuous light or converted to protochlorophyllide in darkness [Shalygo et al. (1998) J Photochem Photobiol 42: 151–158]. We were interested to elucidate the differences in the phototoxicity of uroporphyrin and protochlorophyllide in the CsCI-treated leaves. Photosensitization and the induction of oxidative stress responses in the barley leaves occurred much faster upon protochlorophyllide than upon uroporphyrin accumulation. We compared the time resolved changes in the pool sizes of low molecular weight antioxidants, such as ascorbate, glutathione and tocopherol, as well as of the enzymatic activities of catalase, ascorbate peroxidase, glutathione reductase and superoxide dismutase in illuminated barley leaves which accumulated uroporphyrin or protochlorophyllide. A rapid loss of the antioxidant levels correlated with the accumulation of reactive oxygen species. The contents of low molecular weight antioxidants and the activities of most of the antioxidative enzymes declined more rapidly in the presence of protochlorophyllide than of uroporphyrin. Due to its high lipophilicity, free protochlorophyllide is associated with biomembranes. Therefore, it is assumed that it exerts its phototoxic effects to membranes more rapidly than uroporphyrin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006424216207
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  • 10
    Electronic Resource
    Electronic Resource
    Isolation and characterisation of tobacco (Nicotiana tabacum) cDNA clones encoding proteins involved in magnesium chelation into protoporphyrin IX (1997)
    Springer
    Plant molecular biology 35 (1997), S. 1053-1056 
    Details
    ISSN: 1573-5028
    Keywords: chlorophyll synthesis ; porphyrins ; RACE ; chloroplast ; Fe chelatase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We have identified cDNA clones encoding the two Mg chelatase subunits CHL I and CHL H from tobacco (Nicotiana tabacum) by screening a cDNA library with homologous cDNA fragments from Arabidopsis thaliana. A full-length Chl I cDNA clone encodes a peptide with 426 amino acids. The entire cDNA sequence encoding 1382 amino acid long CHL H was obtained by extension of a truncated cDNA fragment using the ‘rapid amplification of cDNA ends’ (RACE) method. Both genes Chl I and Chl H were strongly expressed in young leaves and to a lesser extent in mature leaves. Only traces of both transcripts were found in flowering organs. Southern blot analysis suggests that CHL I is encoded by a single gene and CHL H most likely by several genes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005913315905
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