The distribution of non-histone nuclear antigens was studied during early somatic embryogenesis of carrot using nuclear antibodies specific for small nuclear RNPs (snRNPs), nuclear matrix proteins and nucleolar proteins. Immunofluorescence showed that in interphase cells snRNPs and nuclear matrix proteins were localized in the nucleus with a speckled pattern. Immunoelectron microscopy indicated that the snRNPs were irregularly distributed while the nuclear matrix proteins showed a distribution preferentially over the condensed chromatin. None were localized in the nucleolus. The nucleolar proteins were localized in both dense fibrillar and granular components while the fibrillar centres were devoid of gold particles. The localization of these antibodies in plant cell nuclei, in a way comparable to the patterns described in animal cells, indicates the general presence of snRNPs in all eukaryotic nuclei. It further confirms the relation of the nuclear matrix proteins to plant cell proliferation events and the possible role of the nucleolar proteins in both rRNA transcription and preribosome assembly.
