Previously it has been found that in tobacco callus cells nucleolar vacuoles repeatedly form and contract. In this study, nucleolar vacuoles were investigated by using radioautography, actinomycin D, and electron microscopy. It was found, from grain counts of nucleoli labeled with uridine-3H, that nucleoli containing vacuoles had more than three times as many grains/µ2 of nucleolar substance as did nucleolei without vacuoles. Treatment of tobacco callus cells with various concentrations of actinomycin D caused the percentage of cells containing nucleolar vacuoles to decrease; with the highest concentration the percentage of these cells dropped from the normal level of about 70% to less than 10%. However, after removal of actinomycin D the cells regained nucleolar vacuoles up to the control level. When radioautography was used with actinomycin D, it was found that the actinomycin D inhibited the uptake of uridine-3H, i.e. inhibited RNA synthesis, in those nucleoli which lost their nucleolar vacuoles. In addition, after removal of the cells from actinomycin D, it was found that as the cells regained nucleolar vacuoles the nucleoli also began to incorporate uridine-3H. Electron micrographs showed the nucleoli to be composed of a compact, finely fibrous central portion surrounded by a layer of dense particles 100–150 A in diameter. Nucleolar vacuoles occurred in the fibrous central portion. Dense particles similar to those in the outer layer of the nucleoli were found scattered throughout the vacuoles and in a dense layer at their outer edge. These data suggest that in cultured tobacco callus cells the formation and contraction of nucleolar vacuoles is closely related to RNA synthesis in the nucleolus.
Article| November 01 1969
A STUDY OF NUCLEOLAR VACUOLES IN CULTURED TOBACCO CELLS USING RADIOAUTOGRAPHY, ACTINOMYCIN D, AND ELECTRON MICROSCOPY
J. Morris Johnson
From the Whitman Laboratory, The University of Chicago, Chicago, Illinois 60637.
Dr. Johnson's present address is Department of Science and Mathematics, Oregon College of Education, Monmouth, Oregon 97361
Received: December 03 1968
Revision Received: June 22 1969
Online Issn: 1540-8140
Print Issn: 0021-9525
Copyright © 1969 by The Rockefeller University Press.
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J. Morris Johnson; A STUDY OF NUCLEOLAR VACUOLES IN CULTURED TOBACCO CELLS USING RADIOAUTOGRAPHY, ACTINOMYCIN D, AND ELECTRON MICROSCOPY . J Cell Biol 1 November 1969; 43 (2): 197–206. doi: https://doi.org/10.1083/jcb.43.2.197
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