title: Immuno-cytochemical localization of indole-3-acetic acid during induction of somatic embryogenesis in cultured sunflower embryos.
abstract: Immature zygotic embryos of sunflower (Helianthus annuus L.) produce somatic embryos when cultured on medium supplemented with a cytokinin as the sole source of exogenous growth regulators. The timing of the induction phase and subsequent morphogenic events have been well characterized in previous work. We address here the question of the role of endogenous indole-3-acetic acid (IAA), since auxins are known to have a crucial role in the induction of somatic embryogenesis in many other culture and regeneration systems. The fact that in the sunflower system no exogenous auxin is required for the induction of somatic embryos makes this system very suitable for the study of the internal dynamics of IAA. We used an immuno-cytochemical approach to visualize IAA distribution within the explants before, during and after the induction phase. IAA accumulated transiently throughout cultured embryos during the induction phase. The detected signal was not uniform but certain tissues, such as the root cap and the root meristem, accumulated IAA in a more pronounced manner. IAA accumulation was not restricted to the reactive zone but the kinetics of endogenous variations strikingly mimic the pulse of IAA that is usually provoked by exogenous IAA application. The direct evidence presented here indicates that an endogenous auxin pulse is indeed among the first signals leading to the induction of somatic embryogenesis.
authors.affiliation: Institut de Biologie Moléculaire des Plantes, CNRS et Université Louis Pasteur, 12 rue du Général Zimmer, 67084 Strasbourg Cedex, France. clement.thomas@ibmp-ulp.u-strasbg.fr
authors.forename: Clément
authors.initials: C
authors.lastname: Thomas
authors.forename: Roberte
authors.initials: R
authors.lastname: Bronner
authors.forename: Jean
authors.initials: J
authors.lastname: Molinier
authors.forename: Els
authors.initials: E
authors.lastname: Prinsen
authors.forename: Harry
authors.initials: H
authors.lastname: van Onckelen
authors.forename: Günther
authors.initials: G
authors.lastname: Hahne
mesh_terms: D015084:2,4-Dichlorophenoxyacetic Acid / Q000494:pharmacology; D000225:Adenine / Q000031:analogs & derivatives* / Q000494:pharmacology; D001593:Benzyl Compounds; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology; D046508:Culture Techniques; D003583:Cytokinins / Q000494:pharmacology; D006368:Helianthus / Q000737:chemistry / Q000187:drug effects / Q000196:embryology*; D007150:Immunohistochemistry; D007210:Indoleacetic Acids / Q000378:metabolism* / Q000494:pharmacology; D007701:Kinetin; D010937:Plant Growth Regulators / Q000494:pharmacology; D018515:Plant Leaves / Q000737:chemistry / Q000187:drug effects / Q000196:embryology*; D011687:Purines; D012639:Seeds / Q000737:chemistry / Q000187:drug effects / Q000254:growth & development; D015398:Signal Transduction / Q000187:drug effects; D013997:Time Factors
chemical_list: D001593:Benzyl Compounds; D003583:Cytokinins; D007210:Indoleacetic Acids; D010937:Plant Growth Regulators; D011687:Purines; D015084:2,4-Dichlorophenoxyacetic Acid; C030737:indoleacetic acid; D000225:Adenine; C480551:benzylaminopurine; D007701:Kinetin