| 1. |
- Dejardin, A, et al.
(författare)
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Sugar/osmoticum levels modulate differential abscisic acid-independent expression of two stress-responsive sucrose synthase genes in Arabidopsis
- 1999
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Ingår i: Biochemical Journal. - 0264-6021 .- 1470-8728. ; 344, s. 503-509
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Tidskriftsartikel (refereegranskat)abstract
- Sucrose synthase (Sus) is a key enzyme of sucrose metabolism. Two Sus-encoding genes (Sus1 and Sus2) from Arabidopsis thaliana were found to be profoundly and differentially regulated in leaves exposed to environmental stresses (cold stress, drought or O-2 deficiency). Transcript levels of Sus1 increased on exposure to cold and drought, whereas Sus2 mRNA was induced specifically by O-2 deficiency. Both cold and drought exposures induced the accumulation of soluble sugars and caused a decrease in leaf osmotic potential, whereas O-2 deficiency was characterized by a nearly complete depletion in sugars. Feeding abscisic acid (ABA) to detached leaves or subjecting Arabidopsis ABA-deficient mutants to cold stress conditions had no effect on the expression profiles of Sus1 or Sus2, whereas feeding metabolizable sugars (sucrose or glucose) or non-metabolizable osmotica [poly(ethylene glycol), sorbitol or mannitol] mimicked the effects of osmotic stress on Sus1 expression in detached leaves. By using various sucrose/mannitol solutions, we demonstrated that Sus1 was up-regulated by a decrease in leaf osmotic potential rather than an increase in sucrose concentration itself. We suggest that Sus1 expression is regulated via an ABA-independent signal transduction pathway that is related to the perception of a decrease in leaf osmotic potential during stresses. In contrast, the expression of Sus2 was independent of sugar/osmoticum effects, suggesting the involvement of a signal transduction mechanism distinct from that regulating Sus1 expression. The differential stress-responsive regulation of Sus genes in leaves might represent part of a general cellular response to the allocation of carbohydrates during acclimation processes.
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| 2. |
- Eimert, K, et al.
(författare)
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Cloning and characterization of several cDNAs for UDP-glucose pyrophosphorylase from barley (Hordeum vulgare) tissues
- 1996
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Ingår i: Gene. - 0378-1119 .- 1879-0038. ; 170:2, s. 227-232
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Tidskriftsartikel (refereegranskat)abstract
- Eleven cDNA clones encoding UDP-glucose pyrophosphorylase (UGPase) have been isolated from cDNA libraries prepared from seed embryo, seed endosperm and leaves of barley (Hordeum vulgare L.). The sequences were identical, with the exception of positioning of the poly(A) tail; at least five clones with different polyadenylation sites were found. For a putative full-length cDNA [1775 nucleotides (nt) plus polyadenylation tail], isolated from an embryo cDNA library, an open reading frame of 1419 nt encodes a protein of 473 amino acids (aa) of 51.6 kDa. An alignment of the derived aa sequence with other UGPases has revealed high identity to UGPases from eukaryotic tissues, but not from bacteria. Within the aa sequence, no homology was found to a UDP-glucose-binding motif that has been postulated for a family of glucosyl transferases. The derived aa sequence of UGPase contains three putative N-glycosylation sites and has a highly conserved positioning of five Lys residues, previously shown to be critical for catalysis and substrate binding of potato tuber UGPase. A possible role for N-glycosylation in the intracellular targeting of UGPase is discussed.
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| 3. |
- Eimert, K, et al.
(författare)
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Molecular cloning and expression of the large subunit of ADP-glucose pyrophosphorylase from barley (Hordeum vulgare) leaves
- 1997
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Ingår i: Gene. - 0378-1119 .- 1879-0038. ; 189:1, s. 79-82
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Tidskriftsartikel (refereegranskat)abstract
- A cDNA clone, blpl14, corresponding to the large subunit of ADP-glucose pyrophosphorylase (AGPase), has been isolated from a cDNA library prepared from leaves of barley (Hordeum vulgare L.). An open reading frame encodes a protein of 503 aa, with a calculated molecular weight of 54 815. The derived aa sequence contains a putative transit peptide sequence, required for targeting to plastids, and has a highly conserved positioning of critical Lys residues that are believed to be involved in effector binding. The derived aa sequence shows 97% identity with the corresponding protein from wheat, but only 36% identity with AGPase from E. coli. The blpl14 gene is expressed predominantly in leaves and to a lesser degree in seed endosperm, but not roots, of barley.
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| 4. |
- Igamberdiev, A U, et al.
(författare)
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Capacity for NADPH/NADP turnover in the cytosol of barley seed endosperm : The role of NADPH-dependent hydroxypyruvate reductase
- 2000
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Ingår i: Plant physiology and biochemistry (Paris). - 0981-9428 .- 1873-2690. ; 38:10, s. 747-753
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Tidskriftsartikel (refereegranskat)abstract
- Barley (Hordeum vulgare L.) endosperm from developing seeds was found to contain relatively high activities of cytosolic NAD(P)II-dependent hydroxypyruvate reductase (HPR-2) and isocitrate dehydrogenase (ICDH). In contrast, activities of peroxisomal NADH-dependent hydroxypyruvate reductase (HPR-1) and glycolate oxidase as well as cytosolic NAD(P)H-dependent glyoxylate reductase were very low or absent in the endosperm both during maturation and seed germination, indicating the lack of a complete glycolate cycle in this tissue. In addition, activities of cytosolic glucose-6-phosphate dehydrogenase and glyceraldehyde-3-phosphate dehydrogenase were low or absent in the endosperm. The endosperm HPR-2 exhibited similar properties to those of an earlier described HPR-2 from green leaves, e.g. activities with both hydroxypyruvate and glyoxylate, utilization of both NADPH and NADH as cofactors, and a strong uncompetitive inhibition by oxalate (K-i in the order of micromolar). In etiolated leaves, both HPR-1 and HPR-2 were present with the same activity as in green leaves, indicating that the lack of HPR-I in the endosperm is not a general feature of non-photosynthetic tissues. We conclude that the endosperm has considerable capacity for cytosolic NADP/NADPH cycling via HPR-2 and ICDH, the former being possibly involved in the utilization of a serine-derived carbon. (C) 2000 Editions scientifiques et medicales Elsevier SAS.
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| 5. |
- Igamberdiev, A U, et al.
(författare)
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Implications of adenylate kinase-governed equilibrium of adenylates on contents of free magnesium in plant cells and compartments
- 2001
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Ingår i: Biochemical Journal. - 0264-6021 .- 1470-8728. ; 360, s. 225-231
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Tidskriftsartikel (refereegranskat)abstract
- On the basis of the equilibrium of adenylate kinase (AK; EC 2.7.4.3). which interconverts MgATP and free AMP with MgADP and free ADP, an approach has been worked out to calculate concentrations of free magnesium (Mg2+), based on concentrations of total ATP, ADP and AMP in plant tissues and in individual subcellular compartments. Based on reported total adenylate contents, [Mg2+] in plant tissues and organelles varies significantly depending on light and dark regimes, plant age and developmental stage. In steady-state conditions, [Mg2+] in chloroplasts is similar in light and darkness (in the millimolar range), whereas in the cytosol it is very low in the light and increases to about 0.4 mM in darkness. During the dark-to-light transition (photosynthetic induction), the [Mg2+] in chloroplasts falls to low values (0.2 mM or less), corresponding to a delay in photosynthetic oxygen evolution. This delay is considered to result from lower activities of Mg-dependent enzymes in the Calvin cycle. In mitochondria, the changes in [Mg2+] are similar but smoother. On the other hand, when the transition from light to darkness is considered, an initial increase in [Mg2+] occurs in both chloroplasts and mitochondria, which may be of importance for the control of key regulatory enzymes (e.g. mitochondrial malic enzyme and pyruvate dehydrogenase complex) and for processes connected with light-enhanced dark respiration. A rationale is presented for a possible role of [MgATP]/[MgADP] ratio (rather than [ATP(total)]/[ADP(total)]) as an important component of metabolic cellular control. It is postulated that assays of total adenylates may provide an accurate measure of [Mg2+] in plant tissues/cells and subcellular compartments, given that the adenylates are equilibrated by AK.
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| 6. |
- Igamberdiev, A U, et al.
(författare)
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Membrane potential, adenylate levels and Mg2+ are interconnected via adenylate kinase equilibrium in plant cells
- 2003
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Ingår i: Biochimica et Biophysica Acta - Bioenergetics. - : Elsevier BV. - 0005-2728 .- 1879-2650. ; 1607:2-3, s. 111-119
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Tidskriftsartikel (refereegranskat)abstract
- Concentrations of adenylate species and free magnesium (Mg2+) within cells are mediated by the equilibrium governed by adenylate kinase (AK), the enzyme abundant in plants in chloroplast stroma and intermembrane spaces of chloroplasts and mitochondria. Ratios of free and Mg-bound adenylates (linked to the values of [Mg2+] established under AK equilibrium) can be rationalized in terms of the overall dependence of concentrations of Mg2+ and free and Mg-bound adenylates, as well as electric potential values across the inner membranes of mitochondria and chloroplasts. The potential across the inner mitochondrial membrane, by driving adenylate translocators, equilibrates free adenylates across the inner membrane according to the Nernst equation and contributes to the ATP(total)/ADP(total) ratio in the cytosol. The ratio affects the exchange of free adenylates with chloroplasts and this, in turn, influences the value of potential across the inner chloroplast membrane. From measurements of subcellular ATP(total)/ADP(total) ratios, we suggest a method of estimating the values of potential across inner membranes of mitochondria and chloroplasts in vivo, which allows a comparison of the operation of these organelles under different physiological conditions. We discuss also how the equilibration of adenylates by AK drives adenylate transport across membranes, and establishes [Mg2+] in the cytosol and chloroplast stroma, maintaining the rates of photosynthesis and respiration. This provides a tool for metabolomic research, by which the determined concentrations of adenylate species could be used for computation of essential metabolic parameters in the cell and in subcellular compartments. (C) 2003 Elsevier B.V. All rights reserved.
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| 7. |
- Igamberdiev, A U, et al.
(författare)
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Origins and metabolism of formate in higher plants
- 1999
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Ingår i: Plant physiology and biochemistry (Paris). - 0981-9428 .- 1873-2690. ; 37:7-8, s. 503-513
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Forskningsöversikt (refereegranskat)abstract
- Formate, a simple one-carbon compound, is readily metabolized in plant tissues. In greening potato tubers, similar to some procaryotes, formate is directly synthesized via a ferredoxin-dependent fixation of CO2, serving as the main precursor for carbon skeletons in biosynthetic pathways. In other plant species and tissues, formate appears as a side-product of photorespiration and of fermentation pathways, but possibly also as a product of direct CO2 reduction in chloroplasts. Formate metabolism is closely related to serine synthesis and to all subsequent reactions originating from serine. Formate may have a role in biosynthesis of numerous compounds, in energetic metabolism and in si,signal transduction pathways related to stress response. This review summarizes the current state of formate research, physiological/biochemical and molecular aspects. (C) Elsevier, Paris.
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| 8. |
- Luo, C, et al.
(författare)
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Differential processing of homologues of the small subunit of ADP-glucose pyrophosphorylase from barley (Hordeum vulgare) tissues
- 1997
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Ingår i: Zeitschrift für Naturforschung C - A Journal of Biosciences. - 0939-5075 .- 1865-7125. ; 52:11-12, s. 807-811
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Tidskriftsartikel (refereegranskat)abstract
- ADP-glucose pyrophosphorylase (AGPase), a two-gene-encoded enzyme, is the key component of starch synthesis in all plants. In the present study, we have used an E. coli expres sion system for the (over)production of proteins derived from both full length and specifically truncated cDNAs encoding small subunits of AGPase from seed endosperm (AGPase-B1) and leaves (AGPase-B2) of barley (Hordeum vulgare). Based on immunoblot analyses, the molecular mass of the expressed AGPase-B1 (52 kD) was similar to that from endosperm extracts, whereas the expressed AGPase-B2 (56 kD) was larger than that in barley leaves (51 kD). Expression of truncated cDNAs for both the seed and leaf proteins has allowed for a direct verification of molecular masses that were earlier proposed for mature AGPases in barley tissues. The data suggest that seed AGPase-B1 does not undergo any post-translational proteolytic processing in barley, whereas the leaf homologue is processed to a smaller protein. Possible implications of these findings are discussed.
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| 9. |
- Siedlecka, A, et al.
(författare)
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The small subunit ADP-glucose pyrophosphorylase (ApS) promoter mediates okadaic acid-sensitive uidA expression in starch-synthesizing tissues and cells in Arabidopsis
- 2003
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Ingår i: Planta. - : Springer Science and Business Media LLC. - 0032-0935 .- 1432-2048. ; 217:2, s. 184-192
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Tidskriftsartikel (refereegranskat)abstract
- Transgenic plants of Arabidopsis thaliana Heynh., transformed with a bacterial beta-glucuronidase (GUS) gene under the control of the promoter of the small subunit (ApS) of ADP-glucose pyrophosphorylase (AGPase), exhibited GUS staining in leaves (including stomata), stems, roots and flowers. Cross-sections of stems revealed GUS staining in protoxylem parenchyma, primary phloem and cortex. In young roots, the staining was found in the root tips, including the root cap, and in vascular tissue, while the older root-hypocotyl axis showed prominent staining in the secondary phloem and paratracheary parenchyma of secondary xylem. The GUS staining co-localized with ApS protein, as found by tissue printing using antibodies against ApS. Starch was found only in cell and tissue types exhibiting GUS staining and ApS labelling, but not in all of them. For example, starch was lacking in the xylem parenchyma and secondary phloem of the root-hypocotyl axis. Sucrose potently activated ApS gene expression in leaves of wild-type (wt) plants, and in transgenic seedlings grown on sucrose medium where GUS activity was quantified with 4-methylumbelliferyl-beta-glucuronide as substrate. Okadaic acid, an inhibitor of protein phosphatases 1 and 2A, completely blocked expression of ApS in mature leaves of wt plants and prevented GUS staining in root tips and flowers of the transgenic plants, suggesting a similar signal transduction mechanism for ApS expression in various tissues. The data support the key role of AGPase in starch synthesis, but they also underlie the ubiquitous importance of the ApS gene for AGPase function in all organs/tissues of Arabidopsis.
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| 10. |
- Sokolov, L N, et al.
(författare)
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Sugars and light/dark exposure trigger differential regulation of ADP-glucose pyrophosphorylase genes in Arabidopsis thaliana (thale cress)
- 1998
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Ingår i: Biochemical Journal. - 0264-6021 .- 1470-8728. ; 336, s. 681-687
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Tidskriftsartikel (refereegranskat)abstract
- Expression of four Arabidopsis (thale cress) genes corresponding to the small (ApS) and large subunits (ApL1, ApL2, ApL3) of ADP-glucose pyrophosphorylase (AGPase), a key enzyme of starch biosynthesis, was found to be profoundly and differentially regulated by sugar and light/dark exposures. Transcript levels of both ApL2 and ApL3, and to a lesser extent ApS, increased severalfold upon feeding sucrose or glucose to the detached leaves in the dark, whereas the mRNA content for ApL1 decreased under the same conditions. Glucose was, in general, less effective than sucrose in inducing regulation of AGPase genes, possibly due to observed limitations in its uptake when compared with sucrose uptake by detached leaves. Osmotic agents [sorbitol, poly(ethylene glycol)] had no effect on ApS, ApL2 and ApL3 transcript level, but they did mimic the effect of sucrose on ApL1 gene, suggesting that the latter is regulated by osmotic pressure rather than any particular sugar. For all the genes the sugar effect was closely mimicked by an exposure of the dark-pre-adapted leaves to the light. Under both dark and light conditions, sucrose fed to the detached leaves was found to be rapidly metabolized to hexoses and, to some extent, starch. Starch production reflected most probably an increase in substrate availability for AGPase reaction rather than being due to changes in AGPase protein content, since both the sugar feeding and light exposure had little or no effect on the activity of AGPase or on the levels of its small and large subunit proteins in leaf extracts. The data suggest tight translational or posttranslational control, but they may also reflect spatial control of AGPase gene expression within a leaf. The sugar/light-dependent regulation of AGPase gene expression may represent a part of a general cellular response to the availability/allocation of carbohydrates during photosynthesis.
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