Journal of Cell Science, Vol 12, 369-383, Copyright © 1973 by Company of Biologists

Submitted on July 14, 1972

An Ultrastructural and Radioautographic Investigation of the Nucleolonemal Component of Plant Interphase Nucleoli

¹ Laboratoire de Biologie cellulaire et moléculaire, Département de Biologie, Faculté des Sciences, Université Laval, Québec 10, Canada

The interphase nucleolus in Allium porrum meristematic cells is characterized by the presence of 1-4 dense fibrillar zones of rather complex organization. Each such zone appears to consist essentially of a convoluted, evacuolated, filamentous structure approximately 1.5 µm in diameter. At the ultrastructural level, these structures exhibit an intricate array of lacunar spaces each of which is surrounded by a dense coating. These lacunae are filled with a loose fibrillar material and the largest ones sometimes also show a dense central core. In appropriate preparations, certain of the peripherally located lacunae are found to be continuous with segments of chromosomes. High-resolution radioautography reveals, moreover, that DNA is present within both the dense and lighter portions of the nucleolar loops. These observations add further support to the hypothesis that the convoluted filamentous structures in question correspond to loops of chromosomal origin and are thus related to the nucleolar organizer.