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  • 1
    ISSN: 1615-6102
    Keywords: Arabinogalactan protein ; Endocytosis ; Nicotiana ; Pollen ; Pollen tube
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Monoclonal antibody PCBC3, raised against stylar extracts fromNicotians, alata flowers, was deduced from enzyme-linked immunosorbent assays and inhibition of immuno-gold labelling on tissue sections to bind specifically to carbohydrate epitopes on arabinogalactan proteins (AGPs) but not to other arabinose-containing cell wall polysaccharides. When pollen grains ofN. tabacum were hydrated in fixative, PCBC3 bound to vesicles in the vicinity of the endoplasmic reticulum but, when grains were hydrated for 20 min in culture medium before fixation, binding was restricted to the plasma membrane. The generative-cell plasma membrane was also labelled in grains ofLycopersicon peruvianum. In pollen tubes ofN. tabacum grown in liquid culture, the AGPs detected by PCBC3 were located in several regions, including the plasma membrane, tubular-vesicular structures (plasmalemmasomes) at and under the plasma membrane, and multilamellar bodies within vacuoles, features generally associated with endocytosis. Labelling was not evident in secretory vesicles or the plasma membrane at the pollen-tube tip. The AGPs detected with PCBC3 were also present in pollen-tube walls, near the interface between the inner, callosic layer and the outer, fibrillar, pectic layer. Pollen tubes ofN. tabacum grown in medium lacking added CuSO4 produce a wall with an abnormally thickened fibrillar layer, and this layer was uniformly labelled with PCBC3. The disposition of wall AGPs thus changes in pollen tubes of different morphologies.
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  • 2
    ISSN: 1615-6102
    Keywords: Nicotiana ; Pollen ; Pollen tube ; Generative nucleus ; Sperm nuclei ; DAPI staining
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Production of sperm cells by division of the generative cell occurs during growth ofNicotiana (tobacco) pollen tubes through the sporophytic tissue of the style, and is associated with transition to the second phase of pollen-tube growth. WhenNicotiana pollen tubes are grown in liquid culture, the extent of generative-nucleus division and the timing of this division depend on the chemical composition of the medium. Addition of reduced forms of nitrogen, either as mixed amino-acids (0.03% w/v of an acid hydrolysate of casein) or as 1 mM ammonium chloride, induces division of the generative nucleus in over 90% of the tubes; 3 mM calcium nitrate does not stimulate division. Individual amino-acids differ in their ability to induce this division. Contaminants in some batches of poly(ethylene glycol), which is a major component of pollen-tube growth media, inhibit generative-nucleus division; this inhibition is greater in the absence of nitrogen, which increases the observed nitrogen-dependence of division. Reduced forms of nitrogen are also required for growth of pollen tubes after division, when callose plugs are deposited. In the absence of nitrogen, growth continues until the point where sperm cell production would normally occur, then ceases. Addition of amino-acids or ammonium chloride thus allows cultured pollen tubes ofNicotiana to progress to their second phase of growth. WhenNicotiana pollen is germinated in a complete culture medium at 25–26°C, sperm nuclei are first observed in the growing tubes after about 10 h, and by about 16 h most of the tubes have undergone division; at lower temperatures, division is delayed. The timing of division also varies between species ofNicotiana, but division occurs similarly in self-compatible and self-incompatible species. Anaphase in an individual pollen tube is calculated to take less than 4 min. The resultant sperm nuclei usually trail behind the vegetative nucleus, but a variety of arrangements of the three nuclei are observed.
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  • 3
    ISSN: 1615-6102
    Keywords: Copper ; Nicotiana ; Pollen ; Pollen tube ; Poly(ethylene glycol) ; Tip growth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Growth of pollen tubes ofNicotiana tabacum W 38 in a defined liquid medium buffered at pH 5.9 and containing sucrose, amino-acids, boric acid, salts and an antibacterial agent was stimulated by the addition of poly(ethylene glycol) 6000 (PEG-6000) and Cu(II) salts. In the absence of both these supplements, up to 50% of the hydrated pollen grains did not develop further, and the germinated tubes were slow-growing and abnormal, with thickened walls, kinked growth, and fragile, swollen tips containing granular cytoplasm. Addition of 10–15% (w/v) purified PEG-6000 increased germination to 80–90% and prevented the progressive bursting of pollen grains and tube tips, but growth was still slow and kinked and tips remained swollen. Addition of 30 μM CuSO4 did not stimulate germination or prevent tip bursting, but produced straight-growing tubes with smooth-sided tips resembling the tips of tubes growing through stylar tissue; the free Cu2+ concentration under these conditions was about 1.0 μM due to chelation by amino-acids, and similar tube morphologies were obtained with 1.0–1.5 μM added CuSO4 when NH4Cl replaced the amino-acids. When the medium containing amino-acids was supplemented with both 12.5% PEG-6000 and 30 μM CuSO4, long-term (48 h) growth of straight pollen tubes with smooth-sided tips, thin walls and long ladders of callose plugs was observed; growth occurred at 250 μm/h, approximately 30–40% of the rate observed in the style. Although omission of CuSO4 from this complete medium severely affected tube growth and callose plug deposition, it did not alter the timing of generative-nucleus division, and thus the different parameters associated with the second phase of pollen-tube growth can be uncoupled in culture. High levels of FeSO4 (300 μM) had a similar morphogenetic effect to CuSO4, but addition of 300 μM L-ascorbate or D-iso-ascorbate was required to prevent precipitation of Fe(III) oxide and prolong the stimulation of pollen-tube growth; EDTA removed the morphogenetic effect of both CuSO4 and FeSO4. Further, an impure grade of PEG-4000 was contaminated with an organic morphogen that allowed continued slow growth of pollen tubes with smooth, straight-sided tips in the absence of added CuSO4 or FeSO4, with tube morphology unaffected by ascorbate or EDTA. However, the long-term morphogenetic effect of trace levels of CuSO4 suggests that Cu(II) salts play an important role in pollen-tube development in at least this species ofNicotiana.
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  • 4
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    Electronic Resource
    Springer
    Planta 191 (1993), S. 470-481 
    ISSN: 1432-2048
    Keywords: Callose ; Callose synthase ; Nicotiana ; Pollen tube ; Protease activation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Pollen-tube cell walls are unusual in that they are composed almost entirely of callose, a (1,3)-β-linked glucan with a few 6-linked branches. Regulation of callose synthesis in pollen tubes is under developmental control, and this contrasts with the deposition of callose in the walls of somatic plant cells which generally occurs only in response to wounding or stress. The callose synthase (uridine-diphosphate glucose: 1,3-β-d-glucan 3-β-d-glucosyl transferase, EC 2.4.1.34) activities of membrane preparations from cultured pollen tubes and suspension-cultured cells of Nicotiana alata Link et Otto (ornamental tobacco) exhibited different kinetic and regulatory properties. Callose synthesis by membrane preparations from pollen tubes was not stimulated by Ca2+ or other divalent cations, and exhibited Michaelis-Menten kinetics only between 0.25 mM and 6 mM uridine-diphosphate glucose (K m 1.5–2.5 mM); it was activated by β-glucosides and compatible detergents. In contrast, callose synthesis by membrane preparations from suspension-cultured cells was dependent on Ca2+, and in the presence of 2 mM Ca2+ exhibited Michaelis-Menten kinetics above 0.1 mM uridine-diphosphate glucose (K m 0.45 mM); it also required a β-glucoside and low levels of compatible detergent for full activity, but was rapidly inactivated at higher levels of detergent. Callose synthase activity in pollen-tube membranes increased ten fold after treatment of the membranes with trypsin in the presence of detergent, with no changes in cofactor requirements. No increase in callose synthase activity, however, was observed when membranes from suspension-cultured cells were treated with trypsin. The insoluble polymeric product of the pollen-tube enzyme was characterised as a linear (1,3)-β-d-glucan with no 6-linked glucosyl branches, and the same product was synthesised irrespective of the assay conditions employed.
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  • 5
    ISSN: 1432-2048
    Keywords: Key words: Callose ; Cellobiohydrolase ; Cellulose ; Nicotiana (pollen tube) ; Pollen grain ; Pollen tube
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. The distribution of cellulose and callose in the walls of pollen tubes and grains of Nicotiana tabacum L. was examined by electron microscopy using gold-labelled cellobiohydrolase for cellulose and a (1,3)-β-D-glucan-specific monoclonal antibody for callose. These probes provided the first direct evidence that cellulose co-locates with callose in the inner, electron-lucent layer of the pollen-tube wall, while both polymers are absent from the outer, fibrillar layer. Neither cellulose nor callose are present in the wall at the pollen-tube tip or in cytoplasmic vesicles. Cellulose is first detected approximately 5–15 μm behind the growing tube tip, just before a visible inner wall layer commences, whereas callose is first observed in the inner wall layer approximately 30 μm behind the tip. Callose was present throughout transverse plugs, whereas cellulose was most abundant towards the outer regions of these plugs. This same distribution of cellulose and callose was also observed in pollen-tube walls of N. alata Link et Otto, Brassica campestris L. and Lilium longiflorum Thunb. In pollen grains of N. tabacum, cellulose is present in the intine layer of the wall throughout germination, but no callose is present. Callose appears in grains by 4 h after germination, increasing in amount over at least the first 18 h, and is located at the interface between the intine and the plasma membrane. This differential distribution of cellulose and callose in both pollen tubes and grains has implications for the nature of the β-glucan biosynthetic machinery.
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  • 6
    ISSN: 1432-2048
    Keywords: Key words: Callose ; Callose synthase ; Nicotiana ; Plasma membrane ; Pollen tube ; Product entrapment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. The callose synthase (UDP-glucose: 1,3-β-d-glucan 3-β-d-glucosyl transferase; EC 2.4.1.34) enzyme (CalS) from pollen tubes of Nicotiana alata Link et Otto is responsible for developmentally regulated deposition of the cell wall polysaccharide callose. Membrane preparations from N. alata pollen tubes grown in liquid culture were fractionated by density-gradient centrifugation. The CalS activity sedimented to the denser regions of the gradient, approximately 1.18 g · ml−1, away from markers for Golgi, endoplasmic reticulum and mitochondria, and into fractions enriched in ATPase activity and in membranes staining with phosphotungstic acid at low pH. This suggests that pollen-tube CalS is localised in the plasma membrane. Callose synthase activity from membranes enriched by downward centrifugation was solubilised with digitonin, which gave a 3- to 4-fold increase in enzyme activity, and the solubilised activity was then enriched a further 10-fold by product entrapment. The complete procedure gave final CalS specific activities up to 1000-fold higher than those of pollen-tube homogenates. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that several polypeptides co-fractionated with CalS activity through purification, with a polypeptide of 190 kDa being enriched in product-entrapment pellets.
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  • 7
    ISSN: 1432-2048
    Keywords: Key words: Callose ; Callose synthase ; Cell wall ; Nicotiana alata ; Pollen tube ; Zymogen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. The callose synthase (CalS) activity of membrane preparations from cultured Nicotiana alata Link & Otto pollen tubes is increased several-fold by treatment with trypsin in the presence of digitonin, possibly due to activation of an inactive (zymogen) form of the enzyme. Active and inactive forms of CalS are also present in stylar-grown tubes. Callose deposition was first detected immediately after germination of pollen grains in liquid medium, at the rim of the germination aperture. During tube growth the 3-linked glucan backbone of callose was deposited at an increasing rate, reaching a maximum of 65 mg h−1 in tubes grown from 1 g pollen. Callose synthase activity was first detected immediately after germination, and then also increased substantially during tube growth. Trypsin caused activation of CalS throughout a 30-h time course of tube growth, but the degree of activation was higher for younger pollen tubes. Over a 10-fold range of callose deposition rates, the assayed CalS activity was sufficient to account for the rate of callose deposition without trypsin activation, implying that the form of CalS active in isolated membranes is responsible for callose deposition in intact pollen tubes. Sucrose-density-gradient centrifugation separated a lighter, intracellular membrane fraction containing only inactive CalS from a heavier, plasma-membrane fraction containing both active and inactive CalS, with younger pollen tubes containing relatively more of the inactive intracellular enzyme. The increasing rate of callose deposition during pollen-tube growth may thus be caused by the transport of inactive forms of CalS from intracellular membranes to the plasma membrane, followed by the regulated activation of these inactive forms in this final location.
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  • 8
    Publication Date: 2015-06-19
    Description: There is an urgent need for new drugs to treat malaria, with broad therapeutic potential and novel modes of action, to widen the scope of treatment and to overcome emerging drug resistance. Here we describe the discovery of DDD107498, a compound with a potent and novel spectrum of antimalarial activity against multiple life-cycle stages of the Plasmodium parasite, with good pharmacokinetic properties and an acceptable safety profile. DDD107498 demonstrates potential to address a variety of clinical needs, including single-dose treatment, transmission blocking and chemoprotection. DDD107498 was developed from a screening programme against blood-stage malaria parasites; its molecular target has been identified as translation elongation factor 2 (eEF2), which is responsible for the GTP-dependent translocation of the ribosome along messenger RNA, and is essential for protein synthesis. This discovery of eEF2 as a viable antimalarial drug target opens up new possibilities for drug discovery.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4700930/" target="_blank"〉〈img src="https://static.pubmed.gov/portal/portal3rc.fcgi/4089621/img/3977009" border="0"〉〈/a〉   〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4700930/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Baragana, Beatriz -- Hallyburton, Irene -- Lee, Marcus C S -- Norcross, Neil R -- Grimaldi, Raffaella -- Otto, Thomas D -- Proto, William R -- Blagborough, Andrew M -- Meister, Stephan -- Wirjanata, Grennady -- Ruecker, Andrea -- Upton, Leanna M -- Abraham, Tara S -- Almeida, Mariana J -- Pradhan, Anupam -- Porzelle, Achim -- Martinez, Maria Santos -- Bolscher, Judith M -- Woodland, Andrew -- Norval, Suzanne -- Zuccotto, Fabio -- Thomas, John -- Simeons, Frederick -- Stojanovski, Laste -- Osuna-Cabello, Maria -- Brock, Paddy M -- Churcher, Tom S -- Sala, Katarzyna A -- Zakutansky, Sara E -- Jimenez-Diaz, Maria Belen -- Sanz, Laura Maria -- Riley, Jennifer -- Basak, Rajshekhar -- Campbell, Michael -- Avery, Vicky M -- Sauerwein, Robert W -- Dechering, Koen J -- Noviyanti, Rintis -- Campo, Brice -- Frearson, Julie A -- Angulo-Barturen, Inigo -- Ferrer-Bazaga, Santiago -- Gamo, Francisco Javier -- Wyatt, Paul G -- Leroy, Didier -- Siegl, Peter -- Delves, Michael J -- Kyle, Dennis E -- Wittlin, Sergio -- Marfurt, Jutta -- Price, Ric N -- Sinden, Robert E -- Winzeler, Elizabeth A -- Charman, Susan A -- Bebrevska, Lidiya -- Gray, David W -- Campbell, Simon -- Fairlamb, Alan H -- Willis, Paul A -- Rayner, Julian C -- Fidock, David A -- Read, Kevin D -- Gilbert, Ian H -- 079838/Wellcome Trust/United Kingdom -- 091625/Wellcome Trust/United Kingdom -- 098051/Wellcome Trust/United Kingdom -- 100476/Wellcome Trust/United Kingdom -- R01 AI090141/AI/NIAID NIH HHS/ -- R01 AI103058/AI/NIAID NIH HHS/ -- England -- Nature. 2015 Jun 18;522(7556):315-20. doi: 10.1038/nature14451.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Drug Discovery Unit, Division of Biological Chemistry and Drug Discovery, College of Life Sciences, University of Dundee, Dundee DD1 5EH, UK. ; Department of Microbiology and Immunology, Columbia University College of Physicians and Surgeons, New York, New York 10032, USA. ; Malaria Programme, Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Cambridge CB10 1SA, UK. ; Department of Life Sciences, Imperial College, London SW7 2AZ, UK. ; University of California, San Diego, School of Medicine, 9500 Gilman Drive 0760, La Jolla, California 92093, USA. ; Global Health and Tropical Medicine Division, Menzies School of Health Research, Charles Darwin University, PO Box 41096, Casuarina, Darwin, Northern Territory 0811, Australia. ; Department of Global Health, College of Public Health University of South Florida, 3720 Spectrum Boulevard, Suite 304, Tampa, Florida 33612, USA. ; GlaxoSmithKline, Tres Cantos Medicines Development Campus-Diseases of the Developing World, Severo Ochoa 2, Tres Cantos 28760, Madrid, Spain. ; TropIQ Health Sciences, Geert Grooteplein 28, Huispost 268, 6525 GA Nijmegen, The Netherlands. ; Centre for Drug Candidate Optimisation, Monash University, 381 Royal Parade, Parkville, Victoria 3052, Australia. ; Eskitis Institute, Brisbane Innovation Park, Nathan Campus, Griffith University, Queensland 4111, Australia. ; Malaria Pathogenesis Laboratory, Eijkman Institute for Molecular Biology, Jalan Diponegoro 69, 10430 Jakarta, Indonesia. ; Medicines for Malaria Venture, PO Box 1826, 20 route de Pre-Bois, 1215 Geneva 15, Switzerland. ; Swiss Tropical and Public Health Institute, Socinstrasse 57, 4051 Basel, Switzerland. ; 1] Global Health and Tropical Medicine Division, Menzies School of Health Research, Charles Darwin University, PO Box 41096, Casuarina, Darwin, Northern Territory 0811, Australia [2] Centre for Tropical Medicine and Global Health, Nuffield Department of Medicine, University of Oxford, Oxford OX3 7LJ, UK. ; 1] Department of Microbiology and Immunology, Columbia University College of Physicians and Surgeons, New York, New York 10032, USA [2] Division of Infectious Diseases, Department of Medicine, Columbia University College of Physicians and Surgeons, New York, New York 10032, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26085270" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Antimalarials/administration & dosage/adverse ; effects/pharmacokinetics/*pharmacology ; Drug Discovery ; Female ; Gene Expression Regulation/*drug effects ; Life Cycle Stages/drug effects ; Liver/drug effects/parasitology ; Malaria/drug therapy/*parasitology ; Male ; Models, Molecular ; Peptide Elongation Factor 2/antagonists & inhibitors/metabolism ; Plasmodium/*drug effects/genetics/growth & development/*metabolism ; Plasmodium berghei/drug effects/physiology ; Plasmodium falciparum/drug effects/metabolism ; Plasmodium vivax/drug effects/metabolism ; Protein Biosynthesis/*drug effects ; Quinolines/administration & dosage/chemistry/pharmacokinetics/*pharmacology
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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