Distribution of rDNA in the nucleus of Giardia lamblia: detection by Ag-I silver stain.
Previous investigations have proved that diplomonads have primitive cell nuclei and lack a nucleolus. We determined the distribution of ribosomal DNA (rDNA) in diplomonad nuclei that lacked a nucleolus. Giardia lamblia was used as the experimental organism with Euglena gracilis as the control. The distribution of rDNA was demonstrated indirectly by the modified Ag-I silver technique that can indicate specifically the nucleolus organizing region (NOR) by both light and electron microscopy. In ultrathin sections of silver stained Euglena cells, all silver grains were concentrated in the fibrosa of the nucleolus, while no silver grains were found in the cytoplasm, nucleoplasm, condensed chromosomes or pars granulosa of the nucleus. In the silver stained Giardia cells, no nucleolus was found, but a few silver grains were scattered in the nucleus. This suggests that the rDNA of Giardia does not form an NOR-like structure and that its nucleus is in a primitive state.
Guo
J
J
College of Life Science, Nanjing Normal University, Nanjing, 210097, P.R. China. jguo58@yahoo.com
Chen
Y
Y
Zhou
K
K
Li
J
J
D000818:Animals; D002466:Cell Nucleolus / Q000648:ultrastructure; D002467:Cell Nucleus / Q000648:ultrastructure*; D004275:DNA, Ribosomal / Q000378:metabolism* / Q000648:ultrastructure*; D016829:Giardia lamblia / Q000648:ultrastructure*; D009697:Nucleolus Organizer Region / Q000648:ultrastructure; D016622:Silver Staining
D004275:DNA, Ribosomal