A cytochemical and radioautographic study of the ultrastructural organization of puff-like fibrillar structures in plant interphase nuclei (Allium porrum)

A cytochemical and radioautographic study of the ultrastructural organization of puff-like fibrillar structures in interphase nuclei of plant meristematic cells (Allium porrum) was performed. Roots were fixed with either formaldehyde or glutaraldehyde before cytochemical testing for DNA, RNA and proteins. Some specimens were labelled with 3H-thymidine for high-resolution radioautographic observations. Staining with diaminobenzidine (DAB) revealed that nuclear puff-like formations consisted partly of a loose fibrillar meshwork containing nucleic acids. Part of this fine fibrillar reticulum persisted whether the preparations were digested with DNase or RNase before staining with DAB indicating that these nuclear structures contained both DNA and RNA. These formations also incorporated thymidine suggesting that they corresponded to specific chromosome segments. Staining with ethanolic phosphotungstic acid or digestion of specimens with proteinase K showed that these loose fibrillar structures also consisted of proteins. Judging from their ultrastructure, their association with the chromatin reticulum and their cytochemical characteristics, these nuclear formations most likely correspond to centromeres. Since DNA is present within these structures it is possible to distinguish them from other spherical nuclear formations, observed in certain plant species, generally referred to as karyosomes or micronucleoli which appear to consist of ribonucleoproteins. (author)