NUCLEOLAR EVOLUTION AND COILED BODIES DURING MEIOTIC PROPHASE IN OLEA-EUROPAEA - DIFFERENTIAL LOCALIZATION OF NUCLEIC-ACIDS

We studied the ultrastructural evolution of the nucleolus during meiot ic prophase in olive microsporocytes. During prophase, nuclear bodies morphologically similar to coiled bodies were observed. The nucleic ac id composition of these bodies was examined in microsporocytes using e lectron microscopic techniques with EDTA preferential ribonucleoprotei n staining, anti-DNA immunolabeling, the in situ terminal deoxynucleot idyl transferase-immunogold technique, and in situ hybridization with 188 rRNA and U3 snoRNA digoxigenin-labeled probes. The ultrastructural appearance of the meiocyte nucleolus indicated a low level of activit y from the early prophase stage: the granular component was practicall y absent and nucleoli were constituted almost exclusively by dense fib rillar component containing large fibrillar centers that lacked chroma tin inclusions. However, the appearance of reactivation vacuoles in th e nucleolus during zygotene and high levels of rRNA in the nucleoplasm during pachytene support the presence of a peak in rRNA synthesis. Ou r results also show that the nuclear bodies that appear during prophas e I are ribonucleoproteinaceous in nature; neither DNA nor ribosomal R NA were detected. The presence of U3 snoRNA, as shown by in situ hybri dization in nuclear bodies from plant material, is also evidence that these structures are coiled bodies. We suggest that coiled bodies are involved not only in pre-and post-splicing events but also in the stor age, transport or recycling of rRNA maturation elements.