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  • Kopriva, Stanislav  (20)
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  • 1
    In: Journal of Experimental Botany, 2010, 2009, Vol. 61(2), pp.609-622
    Description: Sulphate assimilation provides reduced sulphur for the synthesis of cysteine, methionine, and numerous other essential metabolites and secondary compounds. The key step in the pathway is the reduction of activated sulphate, adenosine 5′-phosphosulphate (APS), to sulphite catalysed by APS reductase (APR). In the present study, [ 35 S]sulphur flux from external sulphate into glutathione (GSH) and proteins was analysed to check whether APR controls the flux through the sulphate assimilation pathway in poplar roots under some stress conditions and in transgenic poplars. (i) O -Acetylserine (OAS) induced APR activity and the sulphur flux into GSH. (ii) The herbicide Acetochlor induced APR activity and results in a decline of GSH. Thereby the sulphur flux into GSH or protein remained unaffected. (iii) Cd treatment increased APR activity without any changes in sulphur flux but lowered sulphate uptake. Several transgenic poplar plants that were manipulated in sulphur metabolism were also analysed. (i) Transgenic poplar plants that overexpressed the γ-glutamylcysteine synthetase ( γ-ECS ) gene, the enzyme catalysing the key step in GSH formation, showed an increase in sulphur flux into GSH and sulphate uptake when γ-ECS was targeted to the cytosol, while no changes in sulphur flux were observed when γ-ECS was targeted to plastids. (ii) No effect on sulphur flux was observed when the sulphite oxidase ( SO ) gene from Arabidopsis thaliana , which catalyses the back reaction of APR, that is the reaction from sulphite to sulphate, was overexpressed. (iii) When Lemna minor APR was overexpressed in poplar, APR activity increased as expected, but no changes in sulphur flux were observed. For all of these experiments the flux control coefficient for APR was calculated. APR as a controlling step in sulphate assimilation seems obvious under OAS treatment, in γ -ECS and SO overexpressing poplars. A possible loss of control under certain conditions, that is Cd treatment, Acetochlor treatment, and in APR overexpressing poplar, is discussed.
    Keywords: Aps Synthetase ; Flux Measurements ; Glutathione ; Poplar ; Roots ; Sulphate Uptake ; Sulphite Oxidase
    ISSN: 0022-0957
    E-ISSN: 1460-2431
    Source: Oxford University Press
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  • 2
    Language: English
    In: Journal of experimental botany, 2010, Vol.61(2), pp.609-22
    Description: Sulphate assimilation provides reduced sulphur for the synthesis of cysteine, methionine, and numerous other essential metabolites and secondary compounds. The key step in the pathway is the reduction of activated sulphate, adenosine 5'-phosphosulphate (APS), to sulphite catalysed by APS reductase (APR). In the present study, [(35)S]sulphur flux from external sulphate into glutathione (GSH) and proteins was analysed to check whether APR controls the flux through the sulphate assimilation pathway in poplar roots under some stress conditions and in transgenic poplars. (i) O-Acetylserine (OAS) induced APR activity and the sulphur flux into GSH. (ii) The herbicide Acetochlor induced APR activity and results in a decline of GSH. Thereby the sulphur flux into GSH or protein remained unaffected. (iii) Cd treatment increased APR activity without any changes in sulphur flux but lowered sulphate uptake. Several transgenic poplar plants that were manipulated in sulphur metabolism were also analysed. (i) Transgenic poplar plants that overexpressed the gamma-glutamylcysteine synthetase (gamma-ECS) gene, the enzyme catalysing the key step in GSH formation, showed an increase in sulphur flux into GSH and sulphate uptake when gamma-ECS was targeted to the cytosol, while no changes in sulphur flux were observed when gamma-ECS was targeted to plastids. (ii) No effect on sulphur flux was observed when the sulphite oxidase (SO) gene from Arabidopsis thaliana, which catalyses the back reaction of APR, that is the reaction from sulphite to sulphate, was overexpressed. (iii) When Lemna minor APR was overexpressed in poplar, APR activity increased as expected, but no changes in sulphur flux were observed. For all of these experiments the flux control coefficient for APR was calculated. APR as a controlling step in sulphate assimilation seems obvious under OAS treatment, in gamma-ECS and SO overexpressing poplars. A possible loss of control under certain conditions, that is Cd treatment, Acetochlor treatment, and in APR overexpressing poplar, is discussed.
    Keywords: Glutamate-Cysteine Ligase -- Metabolism ; Oxidoreductases Acting on Sulfur Group Donors -- Metabolism ; Plant Proteins -- Metabolism ; Plants, Genetically Modified -- Physiology ; Populus -- Physiology ; Sulfates -- Metabolism ; Sulfite Oxidase -- Metabolism ; Sulfur -- Metabolism
    ISSN: 00220957
    E-ISSN: 1460-2431
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  • 3
    Language: English
    In: FEBS Letters, 03 June 2010, Vol.584(11), pp.2271-2278
    Description: A key step in sulfate assimilation into cysteine is the reduction of sulfite to sulfide by sulfite reductase (SiR). This enzyme is encoded by three genes in the moss . To obtain a first insight into the roles of the individual isoforms, we deleted the gene encoding the isoform in by homologous recombination and subsequently analysed the Δ mutants. While Δ mutants showed no obvious alteration in sulfur metabolism, their regeneration from protoplasts and their ability to produce mature spores was significantly affected, highlighting an unexpected link between moss sulfate assimilation and development, that is yet to be characterized.
    Keywords: Bryophyte ; Moss Development ; Protonema Development ; Spore Maturation ; Sulfate Assimilation ; Biology ; Chemistry ; Anatomy & Physiology
    ISSN: 0014-5793
    E-ISSN: 1873-3468
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  • 4
    Description: Sulphate assimilation is an essential pathway being a source of reduced sulphur for various cellular processes and for the synthesis of glutathione, a major factor in plant stress defence. Many reports have shown that sulphate assimilation is well co-ordinated with the assimilation of nitrate and carbon. It has long been known that, during nitrate deficiency, sulphate assimilation is reduced and that the capacity to reduce nitrate is diminished in plants starved for sulphate. Only recently, however, was it shown that adenosine 5′ phosphosulphate reductase (APR), the key enzyme of sulphate assimilation, is regulated by carbohydrates. In plants treated with sucrose or glucose APR was induced, whereas the activity was strongly reduced in plants grown in CO 2 -free air. The availability of cysteine is a crucial factor in glutathione synthesis, but an adequate supply of glutamate and glycine are also important. The molecular mechanisms for the co-ordination of S, N, and C assimilation are not known. O -acetylserine, a precursor of cysteine, was proposed to be the signal regulating sulphate assimilation, but most probably is not the outgoing signal to N and C metabolism. cDNA arrays revealed the induction of genes involved in auxin synthesis upon S-starvation, pointing to a possible role of phytohormones. Clearly, despite significant progress in understanding the regulation of sulphate assimilation and glutathione synthesis, their co-ordination with N and C metabolism achieved, and several potential signal molecules identified, present knowledge is still far from being sufficient.
    Keywords: Glutathione Synthesis; Nitrate Deficiency; Nitrate Reduction; Sulphate Assimilation; Regulation
    ISSN: 0022-0957
    E-ISSN: 14602431
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  • 5
    Language: English
    In: Plant physiology, November 2002, Vol.130(3), pp.1406-13
    Description: Cysteine synthesis from sulfide and O-acetyl-L-serine (OAS) is a reaction interconnecting sulfate, nitrogen, and carbon assimilation. Using Lemna minor, we analyzed the effects of omission of CO(2) from the atmosphere and simultaneous application of alternative carbon sources on adenosine 5'-phosphosulfate reductase (APR) and nitrate reductase (NR), the key enzymes of sulfate and nitrate assimilation, respectively. Incubation in air without CO(2) led to severe decrease in APR and NR activities and mRNA levels, but ribulose-1,5-bisphosphate carboxylase/oxygenase was not considerably affected. Simultaneous addition of sucrose (Suc) prevented the reduction in enzyme activities, but not in mRNA levels. OAS, a known regulator of sulfate assimilation, could also attenuate the effect of missing CO(2) on APR, but did not affect NR. When the plants were subjected to normal air after a 24-h pretreatment in air without CO(2), APR and NR activities and mRNA levels recovered within the next 24 h. The addition of Suc and glucose in air without CO(2) also recovered both enzyme activities, with OAS again influenced only APR. (35)SO(4)(2-) feeding showed that treatment in air without CO(2) severely inhibited sulfate uptake and the flux through sulfate assimilation. After a resupply of normal air or the addition of Suc, incorporation of (35)S into proteins and glutathione greatly increased. OAS treatment resulted in high labeling of cysteine; the incorporation of (35)S in proteins and glutathione was much less increased compared with treatment with normal air or Suc. These results corroborate the tight interconnection of sulfate, nitrate, and carbon assimilation.
    Keywords: Oxidoreductases Acting on Sulfur Group Donors ; Araceae -- Metabolism ; Carbon -- Metabolism ; Nitrogen -- Metabolism ; Sulfates -- Metabolism
    ISSN: 0032-0889
    E-ISSN: 15322548
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  • 6
    In: New Phytologist, July 2005, Vol.167(1), pp.73-80
    Description: •  Transition metals such as zinc (Zn) are essential micronutrients for many physiological processes, but they become toxic at elevated levels. Zinc is one of the most abundant trace heavy metals present in agro‐ecosystems. •  Populus spp. have been suggested as good candidates for using to study the removal and/or immobilization of environmental organic and inorganic pollutants. In order to understand the physiological and biochemical bases of this assumption for Zn, plants of Populus deltoides × P. nigra (P. × euramericana) were grown in hydroponics with different concentrations of Zn [1 µm (control), and 1, 5 and 10 mm] in the nutrient solution. •  Shoot biomass decreased at 5 and 10 mm Zn, while the Zn content of young leaves increased progressively with increasing Zn concentration (1–10 mm). Total glutathione (GSH+GSSG) content was reduced with increasing Zn concentration, while the contribution of oxidized to total glutathione increased. Despite these observations, semiquantitative reverse transcription–polymerase chain reaction (RT–PCR) revealed that the gene expression of GSH reductase (GR, chloroplastic and cytosolic isoform) and γ‐glutamylcysteine synthetase (γ‐ECS) increased in young leaves of poplars treated with excess Zn. •  We conclude that GSH synthesis, consumption and redox status play a central role in the response of poplars to high concentrations of Zn.
    Keywords: Antioxidant Defence System ; Glutathione ; Metabolism ; Populus ; Zinc
    ISSN: 0028-646X
    E-ISSN: 1469-8137
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  • 7
    Language: English
    In: Frontiers in Plant Science, Dec 11, 2018
    Description: The aim of present study was to elucidate the significance of the phosphorylated pathway of Ser production for Cys biosynthesis in leaves at day and night and upon cadmium (Cd) exposure. For this purpose, Arabidopsis wildtype plants as control and its psp mutant knocked-down in phosphoserine phosphatase ( PSP ) were used to test if (i) photorespiratory Ser is the dominant precursor of Cys synthesis in autotrophic tissue in the light, (ii) the phosphorylated pathway of Ser production can take over Ser biosynthesis in leaves at night, and (iii) Cd exposure stimulates Cys and glutathione (GSH) biosynthesis and effects the crosstalk of S and N metabolism, irrespective of the Ser source. Glycine (Gly) and Ser contents were not affected by reduction of the psp transcript level confirming that the photorespiratory pathway is the main route of Ser synthesis. The reduction of the PSP transcript level in the mutant did not affect day/night regulation of sulfur fluxes while day/night fluctuation of sulfur metabolite amounts were no longer observed, presumably due to slower turnover of sulfur metabolites in the mutant. Enhanced contents of non-protein thiols in both genotypes and of GSH only in the psp mutant were observed upon Cd treatment. Mutation of the phosphorylated pathway of Ser biosynthesis caused an accumulation of alanine, aspartate, lysine and a decrease of branched-chain amino acids. Knock-down of the PSP gene induced additional defense mechanisms against Cd toxicity that differ from those of WT plants.
    Keywords: Arabidopsis Thaliana – Physiological Aspects ; Phosphatases – Physiological Aspects
    ISSN: 1664-462X
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  • 8
    Description: Glutathione (GSH) is the major low molecular weight thiol in plants with different functions in stress defence and the transport and storage of sulphur. Its synthesis is dependent on the supply of its constituent amino acids cysteine, glutamate, and glycine. GSH is a feedback inhibitor of the sulphate assimilation pathway, the primary source of cysteine synthesis. Sulphate assimilation has been analysed in transgenic poplars ( Populus tremula × P. alba ) overexpressing γ‐glutamylcysteine synthetase, the key enzyme of GSH synthesis, and the results compared with the effects of exogenously added GSH. Although foliar GSH levels were 3–4‐fold increased in the transgenic plants, the activities of enzymes of sulphate assimilation, namely ATP sulphurylase, adenosine 5′‐phosphosulphate reductase (APR), sulphite reductase, serine acetyltransferase, and O ‐acetylserine (thiol)lyase were not affected in three transgenic lines compared with the wild type. Also the mRNA levels of these enzymes were not altered by the increased GSH levels. By contrast, an increase in GSH content due to exogenously supplied GSH resulted in a strong reduction in APR activity and mRNA accumulation. This feedback regulation was reverted by simultaneous addition of O ‐acetylserine (OAS). However, OAS measurements revealed that OAS cannot be the only signal responsible for the lack of feedback regulation of APR by GSH in the transgenic poplars.
    Keywords: Key Words: Adenosine 5′‐phosphosulphate Reductase, Cysteine Synthesis, Glutathione, Poplar, Sulphate Assimilation.
    ISSN: 0022-0957
    E-ISSN: 14602431
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  • 9
    Description: With the aim of analysing the relative importance of sugar supply and nitrogen nutrition for the regulation of sulphate assimilation, the regulation of adenosine 5′‐phosphosulphate reductase (APR), a key enzyme of sulphate reduction in plants, was studied. Glucose feeding experiments with Arabidopsis thaliana cultivated with and without a nitrogen source were performed. After a 38 h dark period, APR mRNA, protein, and enzymatic activity levels decreased dramatically in roots. The addition of 0.5% (w/v) glucose to the culture medium resulted in an increase of APR levels in roots (mRNA, protein and activity), comparable to those of plants kept under normal light conditions. Treatment of roots with d ‐sorbitol or d ‐mannitol did not increase APR activity, indicating that osmotic stress was not involved in APR regulation. The addition of O ‐acetyl‐ l ‐serine (OAS) also quickly and transiently increased APR levels (mRNA, protein, and activity). Feeding plants with a combination of glucose and OAS resulted in a more than additive induction of APR activity. Contrary to nitrate reductase, APR was also increased by glucose in N‐deficient plants, indicating that this effect was independent of nitrate assimilation. [ 35 S]‐sulphate feeding experiments showed that the addition of glucose to dark‐treated roots resulted in an increased incorporation of [ 35 S] into thiols and proteins, which corresponded to the increased levels of APR activity. Under N‐deficient conditions, glucose also increased thiol labelling, but did not increase the incorporation of label into proteins. These results demonstrate that (i) exogenously supplied glucose can replace the function of photoassimilates in roots; (ii) APR is subject to co‐ordinated metabolic control by carbon metabolism; (iii) positive sugar signalling overrides negative signalling from nitrate assimilation in APR regulation. Furthermore, signals originating from nitrogen and carbon metabolism regulate APR synergistically.
    Keywords: Key Words: Adenosine‐5′‐phosphosulphate, Aps Reductase, ‐acetyl‐‐serine, Sulphate Assimilation.
    ISSN: 0022-0957
    E-ISSN: 14602431
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  • 10
    Language: English
    In: Frontiers in Plant Science, Nov 27, 2018
    Description: This study was aimed at elucidating the significance of photorespiratory serine (Ser) production for cysteine (Cys) biosynthesis. For this purpose, sulfur (S) metabolism and its crosstalk with nitrogen (N) and carbon (C) metabolism were analyzed in wildtype Arabidopsis and its photorespiratory bou-2 mutant with impaired glycine decarboxylase (GDC) activity. Foliar glycine and Ser contents were enhanced in the mutant at day and night. The high Ser levels in the mutant cannot be explained by transcript abundances of genes of the photorespiratory pathway or two alternative pathways of Ser biosynthesis. Despite enhanced foliar Ser, reduced GDC activity mediated a decline in sulfur flux into major sulfur pools in the mutant, as a result of deregulation of genes of sulfur reduction and assimilation. Still, foliar Cys and glutathione contents in the mutant were enhanced. The use of Cys for methionine and glucosinolates synthesis was reduced in the mutant. Reduced GDC activity in the mutant downregulated Calvin Cycle and nitrogen assimilation genes, upregulated key enzymes of glycolysis and the tricarboxylic acid (TCA) pathway and modified accumulation of sugars and TCA intermediates. Thus, photorespiratory Ser production can be replaced by other metabolic Ser sources, but this replacement deregulates the cross-talk between S, N, and C metabolism.
    Keywords: Photorespiration – Analysis ; Gene Mutation – Influence ; Arabidopsis Thaliana – Genetic Aspects ; Arabidopsis Thaliana – Composition ; Carbon Fixation – Analysis ; Nitrogen Fixation – Analysis ; Sulfur – Analysis
    ISSN: 1664-462X
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