title: Ultrastructural distribution of DNA within plant meristematic cell nucleoli during activation and the subsequent inactivation by a cold stress.
abstract: We have investigated the precise location of DNA within the meristematic cell nucleolus of Zea mays root cells and Pisum sativum cotyledonary buds, in the course of their activation and induced inactivation following a subsequent treatment at low temperature. For this purpose, we combined the acetylation method, providing an excellent distinction between the various nucleolar components, with the in situ terminal deoxynucleotidyl transferase-immunogold technique, a highly sensitive method for detecting DNA at the ultrastructural level. In addition to the presence of DNA in the condensed chromatin associated with the nucleolus, we demonstrated that a significant label was detected in the nucleolus of quiescent cells in both plant models. Evident labels were also found in the dense fibrillar component of actived nucleoli. Whereas in inactivated nucleoli no significant label was observed within the dense fibrillar component, an intense label was seen over the large heterogeneous fibrillar centres only during inactivation. The granular component was never significantly labelled. These results appear to indicate that the DNA present in the dense fibrillar component of activated nucleoli withdraws from this structure during its inactivation and becomes incorporated in the large fibrillar centres. These observations suggest that in plant cells inactivation of rRNA genes is clearly accompanied by changes in the conformation of ribosomal chromatin.
authors.affiliation: Service de Morphologie Végétale, Université de Liège, Bd du Rectorat B22, Sart-Tilman Liège, B-4000, Belgium.
authors.forename: P
authors.initials: P
authors.lastname: Mineur
authors.forename: A
authors.initials: A
authors.lastname: Jennane
authors.forename: M
authors.initials: M
authors.lastname: Thiry
authors.forename: R
authors.initials: R
authors.lastname: Deltour
authors.forename: G
authors.initials: G
authors.lastname: Goessens
mesh_terms: D002466:Cell Nucleolus / Q000648:ultrastructure*; D002843:Chromatin / Q000648:ultrastructure; D003080:Cold Temperature; D004247:DNA / Q000032:analysis* / Q000648:ultrastructure; D004253:DNA Nucleotidylexotransferase / Q000378:metabolism; D017343:Genes, Plant / Q000235:genetics; D018525:Germination; D007150:Immunohistochemistry; D016253:Microscopy, Immunoelectron; D018532:Pisum sativum / Q000648:ultrastructure*; D012335:RNA, Ribosomal / Q000235:genetics; D003313:Zea mays / Q000648:ultrastructure*
chemical_list: D002843:Chromatin; D012335:RNA, Ribosomal; D004247:DNA; D004253:DNA Nucleotidylexotransferase