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- By Rose Teteki Abbey, K. C. Abraham, David Tuesday Adamo, LeRoy H. Aden, Efrain Agosto, Victor Aguilan, Gillian T. W. Ahlgren, Charanjit Kaur AjitSingh, Dorothy B E A Akoto, Giuseppe Alberigo, Daniel E. Albrecht, Ruth Albrecht, Daniel O. Aleshire, Urs Altermatt, Anand Amaladass, Michael Amaladoss, James N. Amanze, Lesley G. Anderson, Thomas C. Anderson, Victor Anderson, Hope S. Antone, María Pilar Aquino, Paula Arai, Victorio Araya Guillén, S. Wesley Ariarajah, Ellen T. Armour, Brett Gregory Armstrong, Atsuhiro Asano, Naim Stifan Ateek, Mahmoud Ayoub, John Alembillah Azumah, Mercedes L. García Bachmann, Irena Backus, J. Wayne Baker, Mieke Bal, Lewis V. Baldwin, William Barbieri, António Barbosa da Silva, David Basinger, Bolaji Olukemi Bateye, Oswald Bayer, Daniel H. Bays, Rosalie Beck, Nancy Elizabeth Bedford, Guy-Thomas Bedouelle, Chorbishop Seely Beggiani, Wolfgang Behringer, Christopher M. Bellitto, Byard Bennett, Harold V. Bennett, Teresa Berger, Miguel A. Bernad, Henley Bernard, Alan E. Bernstein, Jon L. Berquist, Johannes Beutler, Ana María Bidegain, Matthew P. Binkewicz, Jennifer Bird, Joseph Blenkinsopp, Dmytro Bondarenko, Paulo Bonfatti, Riet en Pim Bons-Storm, Jessica A. Boon, Marcus J. Borg, Mark Bosco, Peter C. Bouteneff, François Bovon, William D. Bowman, Paul S. Boyer, David Brakke, Richard E. Brantley, Marcus Braybrooke, Ian Breward, Ênio José da Costa Brito, Jewel Spears Brooker, Johannes Brosseder, Nicholas Canfield Read Brown, Robert F. Brown, Pamela K. Brubaker, Walter Brueggemann, Bishop Colin O. Buchanan, Stanley M. Burgess, Amy Nelson Burnett, J. Patout Burns, David B. Burrell, David Buttrick, James P. Byrd, Lavinia Byrne, Gerado Caetano, Marcos Caldas, Alkiviadis Calivas, William J. Callahan, Salvatore Calomino, Euan K. Cameron, William S. Campbell, Marcelo Ayres Camurça, Daniel F. Caner, Paul E. Capetz, Carlos F. Cardoza-Orlandi, Patrick W. Carey, Barbara Carvill, Hal Cauthron, Subhadra Mitra Channa, Mark D. Chapman, James H. Charlesworth, Kenneth R. Chase, Chen Zemin, Luciano Chianeque, Philip Chia Phin Yin, Francisca H. Chimhanda, Daniel Chiquete, John T. Chirban, Soobin Choi, Robert Choquette, Mita Choudhury, Gerald Christianson, John Chryssavgis, Sejong Chun, Esther Chung-Kim, Charles M. A. Clark, Elizabeth A. Clark, Sathianathan Clarke, Fred Cloud, John B. Cobb, W. Owen Cole, John A Coleman, John J. Collins, Sylvia Collins-Mayo, Paul K. Conkin, Beth A. Conklin, Sean Connolly, Demetrios J. Constantelos, Michael A. Conway, Paula M. Cooey, Austin Cooper, Michael L. Cooper-White, Pamela Cooper-White, L. William Countryman, Sérgio Coutinho, Pamela Couture, Shannon Craigo-Snell, James L. Crenshaw, David Crowner, Humberto Horacio Cucchetti, Lawrence S. Cunningham, Elizabeth Mason Currier, Emmanuel Cutrone, Mary L. Daniel, David D. Daniels, Robert Darden, Rolf Darge, Isaiah Dau, Jeffry C. Davis, Jane Dawson, Valentin Dedji, John W. de Gruchy, Paul DeHart, Wendy J. Deichmann Edwards, Miguel A. De La Torre, George E. Demacopoulos, Thomas de Mayo, Leah DeVun, Beatriz de Vasconcellos Dias, Dennis C. Dickerson, John M. Dillon, Luis Miguel Donatello, Igor Dorfmann-Lazarev, Susanna Drake, Jonathan A. Draper, N. Dreher Martin, Otto Dreydoppel, Angelyn Dries, A. J. Droge, Francis X. D'Sa, Marilyn Dunn, Nicole Wilkinson Duran, Rifaat Ebied, Mark J. Edwards, William H. Edwards, Leonard H. Ehrlich, Nancy L. Eiesland, Martin Elbel, J. Harold Ellens, Stephen Ellingson, Marvin M. Ellison, Robert Ellsberg, Jean Bethke Elshtain, Eldon Jay Epp, Peter C. Erb, Tassilo Erhardt, Maria Erling, Noel Leo Erskine, Gillian R. Evans, Virginia Fabella, Michael A. Fahey, Edward Farley, Margaret A. Farley, Wendy Farley, Robert Fastiggi, Seena Fazel, Duncan S. Ferguson, Helwar Figueroa, Paul Corby Finney, Kyriaki Karidoyanes FitzGerald, Thomas E. FitzGerald, John R. Fitzmier, Marie Therese Flanagan, Sabina Flanagan, Claude Flipo, Ronald B. Flowers, Carole Fontaine, David Ford, Mary Ford, Stephanie A. Ford, Jim Forest, William Franke, Robert M. Franklin, Ruth Franzén, Edward H. Friedman, Samuel Frouisou, Lorelei F. Fuchs, Jojo M. Fung, Inger Furseth, Richard R. Gaillardetz, Brandon Gallaher, China Galland, Mark Galli, Ismael García, Tharscisse Gatwa, Jean-Marie Gaudeul, Luis María Gavilanes del Castillo, Pavel L. Gavrilyuk, Volney P. Gay, Metropolitan Athanasios Geevargis, Kondothra M. George, Mary Gerhart, Simon Gikandi, Maurice Gilbert, Michael J. Gillgannon, Verónica Giménez Beliveau, Terryl Givens, Beth Glazier-McDonald, Philip Gleason, Menghun Goh, Brian Golding, Bishop Hilario M. Gomez, Michelle A. Gonzalez, Donald K. Gorrell, Roy Gottfried, Tamara Grdzelidze, Joel B. Green, Niels Henrik Gregersen, Cristina Grenholm, Herbert Griffiths, Eric W. Gritsch, Erich S. Gruen, Christoffer H. Grundmann, Paul H. Gundani, Jon P. Gunnemann, Petre Guran, Vidar L. Haanes, Jeremiah M. Hackett, Getatchew Haile, Douglas John Hall, Nicholas Hammond, Daphne Hampson, Jehu J. Hanciles, Barry Hankins, Jennifer Haraguchi, Stanley S. Harakas, Anthony John Harding, Conrad L. Harkins, J. William Harmless, Marjory Harper, Amir Harrak, Joel F. Harrington, Mark W. Harris, Susan Ashbrook Harvey, Van A. Harvey, R. Chris Hassel, Jione Havea, Daniel Hawk, Diana L. Hayes, Leslie Hayes, Priscilla Hayner, S. Mark Heim, Simo Heininen, Richard P. Heitzenrater, Eila Helander, David Hempton, Scott H. Hendrix, Jan-Olav Henriksen, Gina Hens-Piazza, Carter Heyward, Nicholas J. Higham, David Hilliard, Norman A. Hjelm, Peter C. Hodgson, Arthur Holder, M. Jan Holton, Dwight N. Hopkins, Ronnie Po-chia Hsia, Po-Ho Huang, James Hudnut-Beumler, Jennifer S. Hughes, Leonard M. Hummel, Mary E. Hunt, Laennec Hurbon, Mark Hutchinson, Susan E. Hylen, Mary Beth Ingham, H. Larry Ingle, Dale T. Irvin, Jon Isaak, Paul John Isaak, Ada María Isasi-Díaz, Hans Raun Iversen, Margaret C. Jacob, Arthur James, Maria Jansdotter-Samuelsson, David Jasper, Werner G. Jeanrond, Renée Jeffery, David Lyle Jeffrey, Theodore W. Jennings, David H. Jensen, Robin Margaret Jensen, David Jobling, Dale A. Johnson, Elizabeth A. Johnson, Maxwell E. Johnson, Sarah Johnson, Mark D. Johnston, F. Stanley Jones, James William Jones, John R. Jones, Alissa Jones Nelson, Inge Jonsson, Jan Joosten, Elizabeth Judd, Mulambya Peggy Kabonde, Robert Kaggwa, Sylvester Kahakwa, Isaac Kalimi, Ogbu U. Kalu, Eunice Kamaara, Wayne C. Kannaday, Musimbi Kanyoro, Veli-Matti Kärkkäinen, Frank Kaufmann, Léon Nguapitshi Kayongo, Richard Kearney, Alice A. Keefe, Ralph Keen, Catherine Keller, Anthony J. Kelly, Karen Kennelly, Kathi Lynn Kern, Fergus Kerr, Edward Kessler, George Kilcourse, Heup Young Kim, Kim Sung-Hae, Kim Yong-Bock, Kim Yung Suk, Richard King, Thomas M. King, Robert M. Kingdon, Ross Kinsler, Hans G. Kippenberg, Cheryl A. Kirk-Duggan, Clifton Kirkpatrick, Leonid Kishkovsky, Nadieszda Kizenko, Jeffrey Klaiber, Hans-Josef Klauck, Sidney Knight, Samuel Kobia, Robert Kolb, Karla Ann Koll, Heikki Kotila, Donald Kraybill, Philip D. W. Krey, Yves Krumenacker, Jeffrey Kah-Jin Kuan, Simanga R. Kumalo, Peter Kuzmic, Simon Shui-Man Kwan, Kwok Pui-lan, André LaCocque, Stephen E. Lahey, John Tsz Pang Lai, Emiel Lamberts, Armando Lampe, Craig Lampe, Beverly J. Lanzetta, Eve LaPlante, Lizette Larson-Miller, Ariel Bybee Laughton, Leonard Lawlor, Bentley Layton, Robin A. Leaver, Karen Lebacqz, Archie Chi Chung Lee, Marilyn J. Legge, Hervé LeGrand, D. L. LeMahieu, Raymond Lemieux, Bill J. Leonard, Ellen M. Leonard, Outi Leppä, Jean Lesaulnier, Nantawan Boonprasat Lewis, Henrietta Leyser, Alexei Lidov, Bernard Lightman, Paul Chang-Ha Lim, Carter Lindberg, Mark R. Lindsay, James R. Linville, James C. Livingston, Ann Loades, David Loades, Jean-Claude Loba-Mkole, Lo Lung Kwong, Wati Longchar, Eleazar López, David W. Lotz, Andrew Louth, Robin W. Lovin, William Luis, Frank D. Macchia, Diarmaid N. J. MacCulloch, Kirk R. MacGregor, Marjory A. MacLean, Donald MacLeod, Tomas S. Maddela, Inge Mager, Laurenti Magesa, David G. Maillu, Fortunato Mallimaci, Philip Mamalakis, Kä Mana, Ukachukwu Chris Manus, Herbert Robinson Marbury, Reuel Norman Marigza, Jacqueline Mariña, Antti Marjanen, Luiz C. L. Marques, Madipoane Masenya (ngwan'a Mphahlele), Caleb J. D. Maskell, Steve Mason, Thomas Massaro, Fernando Matamoros Ponce, András Máté-Tóth, Odair Pedroso Mateus, Dinis Matsolo, Fumitaka Matsuoka, John D'Arcy May, Yelena Mazour-Matusevich, Theodore Mbazumutima, John S. McClure, Christian McConnell, Lee Martin McDonald, Gary B. McGee, Thomas McGowan, Alister E. McGrath, Richard J. McGregor, John A. McGuckin, Maud Burnett McInerney, Elsie Anne McKee, Mary B. McKinley, James F. McMillan, Ernan McMullin, Kathleen E. McVey, M. Douglas Meeks, Monica Jyotsna Melanchthon, Ilie Melniciuc-Puica, Everett Mendoza, Raymond A. Mentzer, William W. Menzies, Ina Merdjanova, Franziska Metzger, Constant J. Mews, Marvin Meyer, Carol Meyers, Vasile Mihoc, Gunner Bjerg Mikkelsen, Maria Inêz de Castro Millen, Clyde Lee Miller, Bonnie J. Miller-McLemore, Alexander Mirkovic, Paul Misner, Nozomu Miyahira, R. W. L. Moberly, Gerald Moede, Aloo Osotsi Mojola, Sunanda Mongia, Rebeca Montemayor, James Moore, Roger E. Moore, Craig E. Morrison O.Carm, Jeffry H. Morrison, Keith Morrison, Wilson J. Moses, Tefetso Henry Mothibe, Mokgethi Motlhabi, Fulata Moyo, Henry Mugabe, Jesse Ndwiga Kanyua Mugambi, Peggy Mulambya-Kabonde, Robert Bruce Mullin, Pamela Mullins Reaves, Saskia Murk Jansen, Heleen L. Murre-Van den Berg, Augustine Musopole, Isaac M. T. Mwase, Philomena Mwaura, Cecilia Nahnfeldt, Anne Nasimiyu Wasike, Carmiña Navia Velasco, Thulani Ndlazi, Alexander Negrov, James B. Nelson, David G. Newcombe, Carol Newsom, Helen J. Nicholson, George W. E. Nickelsburg, Tatyana Nikolskaya, Damayanthi M. A. Niles, Bertil Nilsson, Nyambura Njoroge, Fidelis Nkomazana, Mary Beth Norton, Christian Nottmeier, Sonene Nyawo, Anthère Nzabatsinda, Edward T. Oakes, Gerald O'Collins, Daniel O'Connell, David W. Odell-Scott, Mercy Amba Oduyoye, Kathleen O'Grady, Oyeronke Olajubu, Thomas O'Loughlin, Dennis T. Olson, J. Steven O'Malley, Cephas N. Omenyo, Muriel Orevillo-Montenegro, César Augusto Ornellas Ramos, Agbonkhianmeghe E. Orobator, Kenan B. Osborne, Carolyn Osiek, Javier Otaola Montagne, Douglas F. Ottati, Anna May Say Pa, Irina Paert, Jerry G. Pankhurst, Aristotle Papanikolaou, Samuele F. Pardini, Stefano Parenti, Peter Paris, Sung Bae Park, Cristián G. Parker, Raquel Pastor, Joseph Pathrapankal, Daniel Patte, W. Brown Patterson, Clive Pearson, Keith F. Pecklers, Nancy Cardoso Pereira, David Horace Perkins, Pheme Perkins, Edward N. Peters, Rebecca Todd Peters, Bishop Yeznik Petrossian, Raymond Pfister, Peter C. Phan, Isabel Apawo Phiri, William S. F. Pickering, Derrick G. Pitard, William Elvis Plata, Zlatko Plese, John Plummer, James Newton Poling, Ronald Popivchak, Andrew Porter, Ute Possekel, James M. Powell, Enos Das Pradhan, Devadasan Premnath, Jaime Adrían Prieto Valladares, Anne Primavesi, Randall Prior, María Alicia Puente Lutteroth, Eduardo Guzmão Quadros, Albert Rabil, Laurent William Ramambason, Apolonio M. Ranche, Vololona Randriamanantena Andriamitandrina, Lawrence R. Rast, Paul L. Redditt, Adele Reinhartz, Rolf Rendtorff, Pål Repstad, James N. Rhodes, John K. Riches, Joerg Rieger, Sharon H. Ringe, Sandra Rios, Tyler Roberts, David M. Robinson, James M. Robinson, Joanne Maguire Robinson, Richard A. H. Robinson, Roy R. Robson, Jack B. Rogers, Maria Roginska, Sidney Rooy, Rev. Garnett Roper, Maria José Fontelas Rosado-Nunes, Andrew C. Ross, Stefan Rossbach, François Rossier, John D. Roth, John K. Roth, Phillip Rothwell, Richard E. Rubenstein, Rosemary Radford Ruether, Markku Ruotsila, John E. Rybolt, Risto Saarinen, John Saillant, Juan Sanchez, Wagner Lopes Sanchez, Hugo N. Santos, Gerhard Sauter, Gloria L. Schaab, Sandra M. Schneiders, Quentin J. Schultze, Fernando F. Segovia, Turid Karlsen Seim, Carsten Selch Jensen, Alan P. F. Sell, Frank C. Senn, Kent Davis Sensenig, Damían Setton, Bal Krishna Sharma, Carolyn J. Sharp, Thomas Sheehan, N. Gerald Shenk, Christian Sheppard, Charles Sherlock, Tabona Shoko, Walter B. Shurden, Marguerite Shuster, B. Mark Sietsema, Batara Sihombing, Neil Silberman, Clodomiro Siller, Samuel Silva-Gotay, Heikki Silvet, John K. Simmons, Hagith Sivan, James C. Skedros, Abraham Smith, Ashley A. Smith, Ted A. Smith, Daud Soesilo, Pia Søltoft, Choan-Seng (C. S.) Song, Kathryn Spink, Bryan Spinks, Eric O. Springsted, Nicolas Standaert, Brian Stanley, Glen H. Stassen, Karel Steenbrink, Stephen J. Stein, Andrea Sterk, Gregory E. Sterling, Columba Stewart, Jacques Stewart, Robert B. Stewart, Cynthia Stokes Brown, Ken Stone, Anne Stott, Elizabeth Stuart, Monya Stubbs, Marjorie Hewitt Suchocki, David Kwang-sun Suh, Scott W. Sunquist, Keith Suter, Douglas Sweeney, Charles H. Talbert, Shawqi N. Talia, Elsa Tamez, Joseph B. Tamney, Jonathan Y. Tan, Yak-Hwee Tan, Kathryn Tanner, Feiya Tao, Elizabeth S. Tapia, Aquiline Tarimo, Claire Taylor, Mark Lewis Taylor, Bishop Abba Samuel Wolde Tekestebirhan, Eugene TeSelle, M. Thomas Thangaraj, David R. Thomas, Andrew Thornley, Scott Thumma, Marcelo Timotheo da Costa, George E. “Tink” Tinker, Ola Tjørhom, Karen Jo Torjesen, Iain R. Torrance, Fernando Torres-Londoño, Archbishop Demetrios [Trakatellis], Marit Trelstad, Christine Trevett, Phyllis Trible, Johannes Tromp, Paul Turner, Robert G. Tuttle, Archbishop Desmond Tutu, Peter Tyler, Anders Tyrberg, Justin Ukpong, Javier Ulloa, Camillus Umoh, Kristi Upson-Saia, Martina Urban, Monica Uribe, Elochukwu Eugene Uzukwu, Richard Vaggione, Gabriel Vahanian, Paul Valliere, T. J. Van Bavel, Steven Vanderputten, Peter Van der Veer, Huub Van de Sandt, Louis Van Tongeren, Luke A. Veronis, Noel Villalba, Ramón Vinke, Tim Vivian, David Voas, Elena Volkova, Katharina von Kellenbach, Elina Vuola, Timothy Wadkins, Elaine M. Wainwright, Randi Jones Walker, Dewey D. Wallace, Jerry Walls, Michael J. Walsh, Philip Walters, Janet Walton, Jonathan L. Walton, Wang Xiaochao, Patricia A. Ward, David Harrington Watt, Herold D. Weiss, Laurence L. Welborn, Sharon D. Welch, Timothy Wengert, Traci C. West, Merold Westphal, David Wetherell, Barbara Wheeler, Carolinne White, Jean-Paul Wiest, Frans Wijsen, Terry L. Wilder, Felix Wilfred, Rebecca Wilkin, Daniel H. Williams, D. Newell Williams, Michael A. Williams, Vincent L. Wimbush, Gabriele Winkler, Anders Winroth, Lauri Emílio Wirth, James A. Wiseman, Ebba Witt-Brattström, Teofil Wojciechowski, John Wolffe, Kenman L. Wong, Wong Wai Ching, Linda Woodhead, Wendy M. Wright, Rose Wu, Keith E. Yandell, Gale A. Yee, Viktor Yelensky, Yeo Khiok-Khng, Gustav K. K. Yeung, Angela Yiu, Amos Yong, Yong Ting Jin, You Bin, Youhanna Nessim Youssef, Eliana Yunes, Robert Michael Zaller, Valarie H. Ziegler, Barbara Brown Zikmund, Joyce Ann Zimmerman, Aurora Zlotnik, Zhuo Xinping
- Edited by Daniel Patte, Vanderbilt University, Tennessee
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- The Cambridge Dictionary of Christianity
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- 05 August 2012
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- 20 September 2010, pp xi-xliv
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The requirement for DNA repair in desiccation tolerance of germinating embryos
- Ivan Boubriak, Haroula Kargiolaki, Linden Lyne, Daphne J. Osborne
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- Seed Science Research / Volume 7 / Issue 2 / June 1997
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- 19 September 2008, pp. 97-106
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It is proposed that desiccation tolerance in the embryo of seeds depends upon the capacity to repair damage to genomic DNA when the desiccated embryo is rehydrated. From a study of imbibed and hydrated embryos of rye (Secale cereale) and wild oat (Avena fatua) evidence is provided that it is neither the extent of water uptake by the cells, the ensuing stability of the DNA to desiccation, nor the onset of S-phase DNA synthesis in the first cell cycle of germination that determines whether the desiccated embryo will survive. It is shown that when α- and β-polymerases of DNA repair are inhibited by aphidicolin and dideoxythymidine-5'-triphosphate, respectively, a γ-irradiation-induced DNA fragmentation cannot be fully repaired. It is shown that in hydrated embryos, at a stage when desiccation tolerance is lost, embryo cells still repair irradiation-induced damage, but this repaired DNA is unstable to desiccation and cannot be rerepaired when water is again made available. The failure to re-repair on rehydration appears to be critical to embryo survival and successful germination.
Function of DNA synthesis and DNA repair in the survival of embryos during early germination and in dormancy
- Rhoderick H. Elder, Daphne J. Osborne
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- Seed Science Research / Volume 3 / Issue 1 / March 1993
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- 19 September 2008, pp. 43-53
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DNA synthesis following the addition of water to excised embryos of non-dormant rye and to embryos of non-dormant and dormant genetic lines of Avena fatua has been examined. All the samples exhibit an early unscheduled DNA synthesis, have similar responses to DNA polymerase inhibitors and a similar increase in DNA ligase function for the first 24 h of imbibition, irrespective of whether they germinate or remain dormant. A β-polymerase-mediated DNA repair activity is indicated immediately upon imbibition with the stable incorporation of 3H-methyl-thymidine into high molecular weight DNA. Following γ-irradiation of dry or imbibed embryos, inhibitor results suggest the appearance of an additional α- or δ-polymerase activity in the ensuing repair. Abscisic acid permits the early unirradiated repair synthesis, but like aphidicolin, it inhibits replicative DNA synthesis and partly inhibits the post-irradiation incorporation of thymidine. DNA synthesis takes place continuously throughout dormancy of imbibed embryos: precursor incorporation into DNA cannot be chased in the short term and occurs in the absence of an S-phase or endoreduplication of nuclear DNA. It is proposed that dormant imbibed embryos maintain the integrity of the genome by a continuous but slow replacement of DNA steered by a non-amplifying and modified form of replicative DNA synthesis and that abscisic acid may play a determining role in this process.
Desiccation and survival in the recalcitrant seeds of Avicennia marina: DNA replication, DNA repair and protein synthesis
- Ivan Boubriak, Mariuccia Dini, Patricia Berjak, Daphne J. Osborne
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- Seed Science Research / Volume 10 / Issue 3 / September 2000
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- 22 February 2007, pp. 307-315
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Abstract An autoradiographic study was made of leucine and thymidine incorporation into the meristematic root primordia and hypocotyl tips of seeds of the recalcitrant mangrove species, Avicennia marina. The investigations show that although there is a temporary reduction of protein synthesis at shedding, root primordia and surrounding hypocotyl cells of the axis never wholly cease incorporation of [3H]leucine and regain pre-shedding levels of activity within a day. Precursor studies using methyl-[3H]thymidine show that, at shedding, there is a temporary cessation of incorporation into root meristem nuclei that lasts no longer than 48 h and, within a day, pre-shedding levels are regained in the meristem nuclei. Analysis of DNA fragmentation patterns in root tips at the time of shedding, and their ability to repair radiation-induced DNA damage, indicate that DNA repair processes are markedly compromised in these cells if water loss reaches 22%. Protein synthesis and DNA replication are reduced by more than half by a water loss of 18% and 16%, respectively. DNA replication does not fully recover on rehydration after only 8% water loss. DNA fragmentation to nucleosomes indicates a programme of cell death at a water loss of 10%. We suggest that the feature of continuous protein synthesis activity with only a temporary interruption in active cell cycling in A. marina root primordia helps to explain both the rapidity in seedling establishment and the extreme vulnerability to desiccation.
An Addiction to Seeds
- Daphne J. Osborne
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- Seed Science Research / Volume 10 / Issue 1 / March 2000
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- 22 February 2007, pp. 3-10
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Hormones, Signals and Target Cells in Plant Development
- Daphne J. Osborne, Michael T. McManus
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- 06 August 2009
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- 11 April 2005
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Meristematic cells in plants become the many different types of cells found in a mature plant. This is achieved by a selective response to chemical signals both from neighbouring cells and distant tissues. It is these responses that shape the plant, its time of flowering, the sex of its flowers, its length of survival or progress to senescence and death. How do plants achieve this? This treatise addresses this question using well-chosen examples to illustrate the concept of target cells. The authors discuss how each cell has the ability to discriminate between different chemical signals, determining which it will respond to and which it will ignore. The regulation of gene expression through signal perception and signal transduction is at the core of this selectivity and the Target Cell concept. This volume will serve as a valuable reference for all researchers working in the field of plant developmental biology.
References
- Daphne J. Osborne, The Open University, Milton Keynes, Michael T. McManus, Massey University, Auckland
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- Hormones, Signals and Target Cells in Plant Development
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- 11 April 2005, pp 205-248
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1 - Introduction
- Daphne J. Osborne, The Open University, Milton Keynes, Michael T. McManus, Massey University, Auckland
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- Hormones, Signals and Target Cells in Plant Development
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Summary
Although it was evident from Darwin's studies of tropisms in plants that informational signals passed from one part of the plant to another, the proof that it was a chemical substance that passed awaited the famous Avena coleoptile experiments of Frits Went (1928). These showed that a molecule (later identified as indole-3-acetic acid [IAA]) was the active agent that was water soluble and would pass across an agar barrier placed between one tissue and another – in his earliest experiments this was between the coleoptile tip (producing IAA) and the IAA-regulated elongating region of the coleoptile below. A tremendous amount of work, both in studying the physiology of this response to IAA, and in identifying the many analogues to IAA, sought the molecular structures required to provide an active molecule. It was from this highly intensive period of plant physiology study that the agricultural revolution of herbicides, defoliants and growth regulators of the 1940s and 1950s was originally generated.
But it was the insect physiologists with their identities of hormone-producing glands and hormone-responding tissues remote from the glands who developed the concepts of target tissues, signalling molecules and receptor sites. Perhaps the most spectacular to record, as an example of the approaches followed later by plant scientists, is the work in the 1930s and 1940s concerning the processes of moulting of larval epidermal skins and of metamorphoses to the adult state (Karlson, 1956).
6 - Terminally Committed Cell Types and the Target Status
- Daphne J. Osborne, The Open University, Milton Keynes, Michael T. McManus, Massey University, Auckland
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- Hormones, Signals and Target Cells in Plant Development
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- 06 August 2009
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- 11 April 2005, pp 117-145
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Cells that we see as permanently committed offer us the opportunity to follow their performance in both excised pieces of plant tissue as well as in planta. With a number of these it has been possible to establish with relative certainty the nature of their target status and the inputs of signals and signalling molecules that they can both perceive and respond to in predictable ways.
Also, it has been possible to follow associations with neighbour cells that influence the pathway to the committed cell state and to deduce certain of the cross-talk and physical communication that leads to a final differentiated condition. Two types of commitment have been considered. The first type is one in which the committed cells remain alive in the body of the plant and their function can therefore be called into operation by the perception of specific signals evoking a one time only response (as is the case with abscission or aleurone cells) or by the differentiation of a response mechanism that can be activated many times without loss of function (as in statocytes and stomata). The second terminally committed cell type to be considered is one that dies in situ amongst its living cell neighbours in the progress of the commitment, but then forms an essential component of the plant's structural architecture and overall function.
7 - The Mechanisms of Target Cell Perception and Response to Specific Signals
- Daphne J. Osborne, The Open University, Milton Keynes, Michael T. McManus, Massey University, Auckland
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- Hormones, Signals and Target Cells in Plant Development
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- 06 August 2009
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- 11 April 2005, pp 146-178
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In previous chapters we outlined the target cell concept, identified the signals and hormones that a cell will encounter and discussed how types of cells can be identified as of particular target status whether during development or on reaching a terminal state of differentiation. Now, over the next chapters, we ask how cells actually recognise signals and question whether the target state dictates, or is dictated by, the mechanisms for signal recognition in vivo. The original description of a hormone, borrowed from the animal world, was a regulatory substance synthesised in one part of the organism and transported to another in which it is recognised and the effect of the hormone becomes manifest. Although the plant has sites of major synthesis of hormone signals and they are all known to be transported, all the evidence tells us that the majority of cells probably contain some level of each hormone and are constantly exposed to the hormones emanating from their neighbours. The plant, after all, is a coenocyte in which all living cells intercommunicate by plasmodesmata and by surface contacts at the cell wall. Of the many signals to which each cell is continuously exposed, why are certain of these perceived and responded to? Or, does a cell respond to all signals that are above a threshold level? If so, how is the threshold level determined and is it fixed or variable?
Animal physiologists deduced the existence of, sought and found receptor proteins on cell surfaces and within the nucleus.
2 - Hormones and Signals: Identification and Description of Signalling Molecules
- Daphne J. Osborne, The Open University, Milton Keynes, Michael T. McManus, Massey University, Auckland
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- Hormones, Signals and Target Cells in Plant Development
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- 06 August 2009
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- 11 April 2005, pp 6-41
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As a first step in developing the target cell concept for plants it is important that the major players in the known informational and signal repertoire are set out briefly at the start of the discussions. There are five major players: auxin, gibberellins, cytokinins, ethylene (and its precursor 1-aminocyclopropane-1-carboxylic acid, ACC), and abscisic acid. The first hormone to be discovered and isolated, auxin, is the best understood, the most important and without doubt the most remarkable. As well, the more recent signal molecules to be discovered are described in greater detail for some of them link more closely to molecules in the animal kingdom.
Auxin
Indole-3-acetic acid (IAA) is the most abundant naturally occurring auxin, with indole-3-butyric acid (IBA) and 4-chloroindole-3-acetic acid (4-Cl-IAA) also occurring naturally (Figure 2.1). IAA was discovered in 1928 by Frits Went (Went, 1928) in the search for the chemical substance that was transported from the apex of the oat coleoptile and caused the cells below to elongate. In higher plants, several pathways of synthesis are possible. IAA is an indole derivative, and both in vivo and in vitro evidence indicates routes of synthesis from the aromatic amino acid, tryptophan, although more recent genetic and biochemical experiments have suggested that tryptophan-independent pathways may also operate to yield the final product (Bartel, 1997).
Auxin biosynthesis
Tryptophan was proposed originally as the precursor of IAA due to structural similarities of the two molecules and when a clearly defined conversion was identified in plant-associated microbes.
Index
- Daphne J. Osborne, The Open University, Milton Keynes, Michael T. McManus, Massey University, Auckland
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Frontmatter
- Daphne J. Osborne, The Open University, Milton Keynes, Michael T. McManus, Massey University, Auckland
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5 - Flexibility of Cell Types and the Target Cell Status
- Daphne J. Osborne, The Open University, Milton Keynes, Michael T. McManus, Massey University, Auckland
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Summary
Every cell can be considered a target cell, with a status that is subject to change throughout its life until a state of terminal differentiation is reached. On this basis, every cell is slightly different from its neighbour with respect to position and signal response, so that at any one time each cell has a unique target status even though it is a member of an apparently uniform tissue. Although the number of signals that have been identified or described so far are limited, the number of responding target cell types in plants would appear to be unlimited.
The flexibility of an individual cell, or perhaps more correctly, the flexibility of a group of cells to give rise by repeated cell divisions to a whole new plant, is the basis of the concept that plant cells remain totipotent throughout their lives. Horticulturists have used this knowledge in vegetative reproduction following observations that many isolated plant parts will readily regenerate new individuals with all the anatomical and behavioural characters of the parent. Planting a cutting is one thing, where all the coordinating signals and target cells are, as it were, still in operational position. Propagation by pieces of tissue where lines of intertissue communication have been lost is quite another.
The question of how a community of cell types in a callus or suspension culture develops in an organised and temporal fashion into a meristem is essentially unresolved though certain clues give consistency to the concept that specific short-distance signals are operating between them.
Contents
- Daphne J. Osborne, The Open University, Milton Keynes, Michael T. McManus, Massey University, Auckland
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9 - The Phenomenon of Hormonal Cross-Talk
- Daphne J. Osborne, The Open University, Milton Keynes, Michael T. McManus, Massey University, Auckland
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Summary
In the last two chapters, discussion has been concerned with the evidence for specific hormone receptors and the downstream signalling events in cells that form part of the transduction chain initiated by the binding of a ligand (the hormone) to its respective receptor. Each major plant hormone has been considered and classified as a separate operational entity, but it is clear that while the same hormone can have different effects in different tissues, a similar response in the same tissue can also be brought about by more than one hormone, the interactions involved being highly dependent upon the genetic background of the tissue in question. With the unravelling of intracellular signalling downstream of hormone perception, it is now becoming clear that more than one signal can utilise a particular transduction pathway. In this final chapter, we refer to examples of such apparently duplicated hormonal responses and how this cross-talk in perception and signalling has been revealed through the use of specific phenotypically expressed mutants. The list is not exhaustive but it serves to illustrate the level of flexibility that a cell can sustain, combined with the basic concept of every cell as an individual target cell.
It has become evident that plants are quite versatile in the cross-talk of their molecular communication language, as represented by situations where one hormone can substitute in function for another.
Preface
- Daphne J. Osborne, The Open University, Milton Keynes, Michael T. McManus, Massey University, Auckland
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This volume presents a conceptual approach to plant cell differentiation that differs in a number of respects from those already present in the literature. We seek to show how every cell has an individual competence to respond to the signal inputs that may impinge upon it and how every cell then has an individual qualitative and quantitative response. Central to this target cell concept is the premise that each cell is selective and can therefore discriminate amongst the many incoming signals to which it is exposed by an ability to perceive them and to respond to them.
Because each cell occupies its individual position within the plant body, the intensity or diversity of the signal inputs that it receives are not themselves identical. Hence, each cell is a unique individual and displays a unique target status even though it may also possess considerable commonality with its neighbours. We define this target status of a cell as the selectivity of its response to a signal and the intensity of that response.
The target cell concept arose originally from notions that were current amongst insect and mammalian scientists stating that a regulatory chemical produced in one organ would be perceived and activated upon by the cells in a distant organ – a specificity that operated between two distinct cell types. As the evidence for specificity of response to hormonal inputs increased during the twentieth century, developmental biologists saw this ability of cells to discriminate amongst the multitude of chemical signals to which they were exposed as a marker of the cell's ability to discriminate between them.
3 - Cell-to-Cell Signalling: Short and Long Distance
- Daphne J. Osborne, The Open University, Milton Keynes, Michael T. McManus, Massey University, Auckland
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Despite enormous biological diversity, uniformity within a species remains remarkably constant. Trees can be instantly recognised by their shape or form, and leaf and flower structures are a basis of identification and classification. Roots conform to each species expectation, and the natural mutant that does not conform to the species type is a rarity.
This means that the society of cells that make up the plant body is under very strict control. No one branch can outgrow its neighbours and distort the overall shape of the tree. The buds that are terminal on any branch keep pace with, but do not outstrip those on the neighbouring branches. The phenomenon of apical dominance, used by crop growers from time immemorial as the basis to reshape by pruning or to improve yields, is intertissue signalling at its most evident. The consistency with which lateral buds will grow when the terminal bud is removed is central to plant culture and pruning systems throughout the world. Not until Frits Went demonstrated the presence of a chemical substance (indole-3-acetic acid) in Avena coleoptile tips and then showed that it would replace the terminal bud in inhibiting the growth of laterals was the first intertissue signal molecule properly established. With the knowledge that the auxin molecule is transported in a polar fashion from cell to cell as it passes from terminal bud to tissues below, it is not difficult to understand how a terminal bud can control the growth of fellow buds below over distances that are relatively short.
8 - Hormone Action and the Relief of Repression
- Daphne J. Osborne, The Open University, Milton Keynes, Michael T. McManus, Massey University, Auckland
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In the previous chapter, we considered the perception of auxin and ethylene in different target tissues. While these hormones were treated separately, the essential mode of action of ethylene and auxin is to relieve a pre-existing repression of response (see Figures 7.2 and 7.4). It is now clear that this mode of action of hormonal signals is widespread amongst plants. In this chapter we look at three further examples, the cytokinins, gibberellins and brassinosteroids, and again examine the evidence for perception of these signals via binding proteins or receptors in different target cells. We additionally examine the evidence that these developmental cues operate through the relief of pre-existing repressions of molecular responses in each cell type examined.
Cytokinin perception in the context of receptors and target cells
Two spectacular events in plant development are attributable to the action of cytokinins. The first, is the conversion of the cells of a callus culture into the organisational complexities of a shoot meristem. Cytokinins act not alone, but in concert with auxin, the ratio of one to the other being critical for optimal organ development. The second is the maintenance of the non-senescent state in specific tissues. Here, cytokinins act as repressors of cell death programmes in many target cell types, most notably those of the leafy tissues of herbaceous plants. Seemingly, there is a requirement for cytokinins primarily synthesised in the root meristems for the retention of metabolic function in the green shoot.
4 - Population Diversity of Cell Types and Target Identification in Higher Plants
- Daphne J. Osborne, The Open University, Milton Keynes, Michael T. McManus, Massey University, Auckland
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Summary
Plants are remarkable in that during evolution from the single cell to the multicell state they developed centres of cell division, the meristems, as the principal repositories of all genetic information. In essence, whether it be the single apical cell of a liverwort or the multicellular dome of tissue of the higher plant, the meristem holds the blueprint of the species. It is only from the divisions of their meristematic cells that the plant body can continuously enlarge and reproduce. Whereas an embryo generates polar identities and a meristematic initiation from the two opposing ends of the zygotic cell, whole plants do not have a restriction to two meristems and they develop unlimited numbers of new primordia as the body of the plant continues to increase in size and cell number.
Anatomists, biochemists, molecular biologists and developmental botanists each see the same plant from different viewpoints. The anatomist studies the structural and visible characters of cells and tissues and describes them accordingly. The biochemist homes in on the functional processes of metabolic control and enzymatic activity attributable to specific plant parts – photosynthetic activity in leaves, for example. The molecular biologist seeks the genetic control of biochemical processes and is particularly attracted to the performance of mutant plants with abnormal behaviour, using them to probe the genetic control of the normal.