Surface Topography and Cytomatrix Elements in Protoplasts from Plant Cells

We studied the surface topography of protoplasts from callus of Daucus sativus(Hofm.) Roehl. and from mesophyll cells of Nicotiana tabacumL. We also followed the distribution of actin elements of the cytomatrix in the subcortical cytoplasm layer. Protoplasts were prepared for scanning electron microscopy by a modified method without drying in the critical point apparatus. After postfixation with OsO₄, carrot and tobacco protoplasts had a similar topography of the surface: it was rough and had few pores. When carrot protoplasts were not postfixed with OsO₄, their surface looked different: it was folded and had 1.5-m pores, which sometimes were bordered with globules 0.3 m in diameter, or it consisted of conical cells varying in depth and size of their bases. We believe that, when protoplasts were not fixed with OsO₄, they lost lipid-containing structures from their surface, and what remained was the protein carcass of the plasmalemma and the underlying layer of the cytoplasm. The inner surface of opened carrot protoplasts had elaborate topography, apparently produced by the elements of the cytomatrix, that is, a relatively thick layer of the cortical cytoplasm, where, using phalloidin–colloidal gold and transmission electron microscopy, we could observe a dense network of actin filaments.