Article Contentsp. 293p. 294p. 295p. 296p. 297p. 298p. 299Issue Table of ContentsAmerican Journal of Botany, Vol. 60, No. 4 (Apr., 1973), pp. 293-396Front Matter [pp. ]Hormone-Induced Endoreduplication Prior to Mitosis in Cultured Pea Root Cortex Cells [pp. 293-299]Promotion of Perithecial Initials in Monacrosporium doedycoides by 6-Methyl Purine [pp. 300-303]Electron Microscopic Observations of Cultured Cells and Protoplasts of Ammi visnaga [pp. 304-312]Photomorphogenesis of the Gametophytes of Lygodium japonicum [pp. 313-321]The Use of a New Clearing Technique for the Study of Early Ovule Development, Megasporogenesis, and Megagametogenesis in Five Species of Cornus L. [pp. 322-338]Monotropa uniflora: Ultrastructural Details of Its Mycorrhizal Habit [pp. 339-345]Conidiogenesis in Ceratocystis ulmi, Ceratocystis piceae, and Graphium penicillioides [pp. 346-354]The Psilopezioid Fungi. III. The Genus Psilopezia (Pezizales) [pp. 355-365]Ibyka Amphikoma, Gen. et sp. n., a New Protoarticulate Precursor from the Late Middle Devonian of New York State [pp. 366-380]Nutritional Requirements for Ovule Formation in Excised Pistils of Nigella [pp. 381-386]Phyllode Theory in Relation to Leaf Ontogeny in Sansevieria trifasciata [pp. 387-395]Back Matter [pp. ]Hormone-Induced Endoreduplication Prior to Mitosis in Cultured Pea Root Cortex CellsAuthor(s): Kornelis R. Libbenga and John G. TorreySource: American Journal of Botany, Vol. 60, No. 4 (Apr., 1973), pp. 293-299Published by: Botanical Society of AmericaStable URL: http://www.jstor.org/stable/2441195 .Accessed: 23/08/2011 15:41Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at .http://www.jstor.org/page/info/about/policies/terms.jspJSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range ofcontent in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new formsof scholarship. For more information about JSTOR, please contact [email protected] Society of America is collaborating with JSTOR to digitize, preserve and extend access to AmericanJournal of Botany.http://www.jstor.orgAmer. J. Bot. 60(4): 293-299. 1973. HORMONE-INDUCED ENDOREDUPLICATION PRIOR TO MITOSIS IN CULTURED PEA ROOT CORTEX CELLS' KORNELIS R. LIBBENGA2 AND JOHN G. TORREY Cabot Foundation, Harvard University, Petersham, Massachusetts 01366 A B S T R A C T One-mm-thick cortical explants excised aseptically from 10-11 mm behind the tip of 3-day- old roots of the garden pea, Pisum sativumn, cv. 'Little Marvel' were cultured on a synthetic nutrient medium supplemented with auxin or auxin and cytokinin. Nuclear DNA contents were measured in cells of the explants at the outset and at specified times during culture up to seven days. Fixed and sectioned preparations were stained with the Feulgen method using the DNA-specific dye auramin-O. Fluorescent microspectro-photometric measurements of indi- vidual nuclei were made from each cortical population. At day zero all cortical nuclei mea- sured were either 2c or 4c with respect to their DNA content. In the presence of the auxins, indoleacetic acid and 2,4-dichlorophenoxyacetic acid, and the cytokinin, kinetin, DNA values increased to multiples of the 2c level with populations at the 8c and 16c level predominating after three days of culture as well as at seven days. In the presence of auxins alone no change in DNA values was observed during three days. Kinetin concentrations as low as 0.01 ppm were already effective. The data are interpreted to show that cytokinin, in the presence of auxin, induces two rounds of DNA synthesis prior to the first mitoses, the first round being connected with chromosome doubling by endoreduplication and the second one with normal mitosis. From this we inferred that tetraploid cells in leguminous root nodules might have arisen in the same way, i.e., by endoreduplication prior to the first mitoses induced by the rhizobial division stimulus, unless the chromosome number of root cortical cells had already been doubled by endoreduplication in the normally differentiating root systems. IN MOST LEGUMINOUS SPECIES root nodules arise in the mature root cortex (Bond, 1948). Two explanations are given for the occurrence of tetra- ploid cells in root nodules. Either the tetraploid cells stem from a preexisting tetraploid cortical cell, which is selectively triggered by the infecting microorganism to divide (Wipf and Cooper, 1940; Nutman, 1965, many others), or the tetraploid cells stem from diploid cortical cells in which the chromosome complement was doubled by endore- duplication brought about by the infecting micro- organism (Bhaskaran and Swaminathan, 1958; Kodama, 1968, 1970). Torrey (1961) found that in pea root segments cultured on a synthetic nu- trient medium auxins trigger divisions in diploid cells and auxins plus cytokinins in tetraploid cells. Since in this system the dividing diploid and tetra- ploid cells belong to two different tissue types, the 1 Received for publication 21 June 1972. This research was supported in part by research grants GM-08145 from the National Institutes of Health, USPHS and GB-31480 from the National Science Foundation, by a fellowship to the senior author from the Netherlands Organization for the Advancement of Pure Research (Z. W. 0.), and by the Cabot Foundation of Harvard University. The authors are indebted to Usha Dhall and Joan Miller for technical assistance. 2 Present address: Department of Experimental Botany, University of Leiden, Nonnensteeg 3, Leiden, the Nether- lands. pericycle and the cortex, respectively, the question remained whether or not auxins plus cytokinins act specifically on preexisting endotetraploid (cor- tical) cells. In order to study this problem we selected the pea cultivar 'Little Marvel' since pre- liminary experiments proved that most mature root cortical cells of this cultivar are diploid. The ex- periments reported here involve the determination of the relative DNA content of individual nuclei of cortical cells before and after culture in a synthetic nutrient medium containing auxins with or without added kinetin. MATERIALS AND METHODS-Culture Methods- The materials and methods used by Torrey and Fosket (1970) were modified for the experiments described here. After surface sterilization, seeds of Pisum sativum, cv. 'Little Marvel' were imbibed