PROTEIN UBIQUINATION IN DIPLOID PARTHENOGENESIS AND EARLY EMBRYOS OF NORWAY SPRUCE

Ontogenetically programmed cell death or apoptosis was initiated in in dividual nuclei by endonucleases and by the ubiquitin-mediated turnove r of proteins. The salvage of degradation products ensured that a nutr ient supply was available for survival of the developing embryos. In d iploid parthenogenesis, the egg-equivalent nucleus underwent parthenog enesis and released proembryos from the egg cytoplasm as the egg cell was eliminated. Immunochemical evidence for the ubiquination of protei ns was found mainly in nucleoli of viable cells in the proembryo, embr yonal group of the early embryo, and throughout nuclei of abortive cel ls. During development of the axial tier of early embryos, the differe ntiation of embryonal suspensors was characterized by enucleation, nuc leolar release, and by the processing of ubiquinated nuclear fragments by proteasome-like associations. Abortive early embryos, which compri sed less than 5% of the population, under went massive apoptosis givin g a strong ubiquitin reactivity with degrading nuclei and chromatin fi bers. Proteins were color-coded by Stains-all as to their location in the axial tier and on SDS-PAGE gels for correlation with Western blots . Regulatory proteins from all cells along the tier were programmed fo r turnover. Ubiquinated, high-molecular-weight proteins in suspensors were released as mucilage into the culture medium. For viable early em bryos, peroxisomes, which encode genes for the ubiquitin-conjugating p rotein family, accounted for the characteristic aceto-carmine staining of the cytoplasm in the embryonal group.