Immuno-gold labelling of tubulin in ultrathin cryosections of cultured carrot cells

Ultrathin cryosections of somatic embryos from carrot suspension cultures were labelled for tubulin with colloidal gold and post-embedded in London Resin White. Good contrast, ultrastructure and antigenicity were preserved. The distribution of immuno-gold labelled tubulin was studied in individual cell organelles. The highest densities of gold particles were found in the cytoplasm, especially the cortical cytoplasm. Nuclei, and notably the nucleoli showed a less intense but positive labelling. The labelling of plastids and mitochondria might be aspecific but it cannot be excluded that some tubulin is present here. Vacuoles and cell walls were negative. Control experiments, in which at least the first antibody was omitted, were negative too. Although the results have to be interpreted carefully, they indicate that differences exist in the distribution of tubulin amongst and within individual cell organelles. The method, therefore, might be useful to study developmental changes in the microtubular cytoskeleton at a high resolution level.