Article Contentsp. 665p. 666p. 667p. 668p. 669p. 670p. 671Issue Table of ContentsAmerican Journal of Botany, Vol. 58, No. 7 (Aug., 1971), pp. 595-696Front Matter [pp. ]Structure and Histogenesis of the Embryo of Acer Saccharinum. I. Embryo Sac and Proembryo [pp. 595-603]Developmental Anatomy in Roots of Ipomoea Purpurea. I. Radicle and Primary Root [pp. 604-615]An Unusual Fossil Fructification from the Jurassic of Oaxaca, Mexico [pp. 616-620]Anatomy of a Lignitized Wood from Senftenberg [pp. 621-626]The Cell Wall Residue of Fossil Wood from Senftenberg [pp. 627-633]Morphology and Anatomy of New Species of Schizaea and Actinostachys [pp. 634-648]A Periodic Acid-Schiff's Substance Related to the Directional Growth of Pollen Tube into Embryo Sac in Paspalum Ovules [pp. 649-654]The Development of the Achene of Polygonum Pensylvanicum: Embryo, Endosperm, and Pericarp [pp. 655-664]The Quiescent Center in Cultured Roots of Convolvulus Arvensis L. [pp. 665-671]Structural Evidence for a Theory of Vein Loading of Translocate [pp. 672-675]The Effect of Various Fixation Schedules on the Scanning Electron Microscopic Image of Tropaeolum Majus [pp. 676-680]Surface Wax Deposits on Foliage of Picea Pungens and Other Conifers [pp. 681-687]Peroxidase Isozymes: A Measure of Molecular Variation in Ten Herbaceous Species of Datura [pp. 688-696]Back Matter [pp. ]The Quiescent Center in Cultured Roots of Convolvulus Arvensis L.Author(s): Harry L. Phillips, Jr. and John G. TorreySource: American Journal of Botany, Vol. 58, No. 7 (Aug., 1971), pp. 665-671Published by: Botanical Society of AmericaStable URL: http://www.jstor.org/stable/2441011 .Accessed: 23/08/2011 15:38Your 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. 58(7): 665-671. 1971. THE QUIESCENT CENTER IN CULTURED ROOTS OF CONVOLVULUS ARVENSIS L.' HARRY L. PHILLIPS, JR. AND JOHN G. TORREY Biological Laboratories, Harvard University, Cambridge, Massachusetts A B S T R A C T Cultured roots of Convolvulus arvensis were incubated in 0.2-0.3,uc/ml methyl-3H-thymidine for different intervals of time. In roots supplied with tritiated thymidine for 12 hr, 14 hr, 48 hr, or 14 hr followed by transfer to fresh medium for 24 hr, autoradiographs prepared of serial, longitudinal sections of the root tips showed the presence of a subterminal quiescent center in the root proper at the distal poles of the central cylinder and cortex. In addition, a zone of un- labelled cells in the columella, distal to the root cap initials, was present. In roots supplied con- tinuously with tritiated thymidine for 64 hr, 96 hr, and 120 hr, the quiescent center was either reduced in size or was not present. THE QUIESCENT CENTER, located subterminally in the apical meristem of elongating roots, was described by Clowes (1956a) as a population of cells which is metabolically inactive and which shows very low rates of cell division. Experiments following by autoradiography the incorporation of labelled precursors of deoxyribonucleic acid syn- thesis, protein synthesis, and the synthesis of insoluble polymers derived from the utilization of sucrose, have shown that quiescent centers are present in different types of roots at different developmental stages (Byrne and Heimsch, 1970; Clowes, 1956a, b, 1958a, b, 1961b; Fisher, 1968; Jensen, Kavaljian, and Martinot, 1960; Raju, Steeves, and Naylor, 1964; Riopel and Steeves, 1964; Thomas, 1967; Thompson and Clowes, 1968; Wilcox, 1962). Rabideau and _'Mericle (1953) studied the distribution of labelled compounds in the meristematic regions of the shoots and roots of corn seedlings by autoradiography after the seedlings had assimilated 14C-carbon dioxide through the leaves for 24 hr. Rabideau and Mericle did not comment on the lack of labelling in the cells of the quiescent center and in the cells of the columella of the root cap, though this lack of labelling is clearly evident in their published autoradiographs. Although Alfieri and Evert (1968) and Miksche and Greenwood (1966) reported the presence of quiescent centers in initial roots of Mledicago sativa L., Trifolium pratense L., and Allium cepa L. and in seedling roots of Glycine max Merr. respectively, their procedures for supplying tritiated thymidine for time periods which did not cover a significant portion of the cell cycle for cells of the apical meristem resulted in autoradiographs which did not sharply delimit the quiescent center. Wimber ' Received for publication 1 February 1971. This research was supported in part by research grant GM-08145 and a fellowship GM-41021 to H. L. P. from the National Institutes of Health, USPHS. (1960), Raju et al. (1964), and Alfieri and Evert (1968) reported that roots formed from cuttings of Tradescantia paludosa, the lateral roots of Euphorbia esula L., and seedling roots of Melilotus alba Desr., respectively, do not contain quiescent centers. However, Clowes (1969) noted that roots of Tradescantia may, in fact, be shown to have a quiescent center consisting of approximately 120 cells. In addition, Clowes and Stewart (1967) and Clowes (1969) noted that the technique used by Raju et al. (1964), which involved handling the lateral roots of Euphorbia, activates the cells of the quiescent center into division. In the case of Melilotus tritiated thymidine was supplied to the roots for a relatively short period of time, namely 1-2 hr. Only those meristematic cells in which DNA was being synthesized were labelled, where- as other meristematic cells not synthesizing DNA, yet having a similar cell cycle, were unlabelled. If the labelled precursor had been available for a longer period of time, such as 12 hr, more cells would have been labelled and a more accurate and reliable delimitation of the quiescent center would have been possible. The quiescent center may be operationally defined as comprising those cells of the apical meristem of the root