Journal of ultrastructure research最新文献

It is argued here that the projections which are frequently seen on the matrix side of the mitochondrial inner membranes and which are characterized as globules or spherical projections or as knob-on-stalks are an artifact of the preparation and/or of the staining of the submitochondrial particles or mitochondria. In sectioned or freeze-fractured preparations of intact cells or mitochondria, the externalized spheres are rarely seen on the membranes. They are, however, almost always seen on fragmented preparations, especially if they have been negatively stained with phosphotungstate.

Beet western yellows virus in vein border parenchyma cells of Pennycress leaves induces some unusual cellular modifications, particularly to the cytoplasmic organelles. Relatively advanced stages of infection were examined in leaves 4 weeks after aphid inoculation with the virus. The most severe ultrastructural modifications occurred in parenchyma cells bordering the veins. The effects included virions in nuclei, virions in cytoplasm, virus vesicles, structural modification to plastids, and appearance of fibrillar inclusions in mitochondria. Oil bodies in the cytoplasm assumed striking proportions. Adjacent cells did not show equivalent changes, and therefore, one may postulate that the border cells show the most adverse effects due to their functional significance in solute transfer.

We have discovered cell-to-cell fusion between fiber cells of adult frog lensesin situ. Stereo scanning electron microscopy (SEM) revealed fusion between neighboring fiber cells in radial cell columns (RCCs) and in the same growth ring, respectively. Cell-to-cell fusion of fiber cells in the lens produced fusion zones that in cross-section were larger and of different polygonal shapes than unfused fiber cells. The shape and sizes of fiber cells surrounding fusion zones and the alignment of RCCs were also altered. Serial sectioning through fusion zones confirmed that they were areas of cell-to-cell continuity established by the union of neighboring fiber cells as seen by SEM. Fusion zones represent a previously unrecognized intercellular pathway in the adult frog lens. Although numerous fusion zones were seen throughout the lens cortex and nucleus, cell-to-cell fusion was rarely observed to have occurred between elongating fiber cells. Interestingly, communicating junctions with an unusual ultrastructure that closely resembles the appearance of membranes in the process of fusion demonstrated in other systems were frequently seen in the region of the superficial cortex where fusion zones were most numerous. The fact that such unusual communicating junctions were not found in any other region of the lens leads us to speculate that structural changes in fiber cell communicating junctions may herald the formation of fusion zones and that the initial site of cell-to-cell fusion between fiber cells may be within communicating junctional plaques.

The new 13+0 axonemal model has been described in the proturanNeocondeellum. All the doublets are devoid of dynein arms and the spermatozoa are immotile. A protruded acrosome is evident in the mature coiled spermatozoa. On the basis of the spermatological results Protentomidae seem closely related to Acerentomidae.

The effects of zinc on the ribonucleoprotein (RNP) constituents of HEp-2 cells have been analyzed. Pulse-chase autoradiographic experiments show a preferential inhibition of nucleolar RNA synthesis and a block in the transport of nucleolar and extranucleolar RNA in zinc-treated cells. Concomitantly with the disturbance in RNA metabolism and in protein synthesis, nucleolar condensation, accumulation of perichromatin granules and fibrils, condensation of interchromatin fibrils, and appearance of dense granular bodies occur. Accumulation of perichromatin fibrils and condensation of interchromatin fibrils appear to be related to the block in the transport of heterogeneous nuclear RNA. Depletion of certain proteins required for the assembly of RNP particles could share in the abnormal behavior of RNA and lead to the accumulation of perichromatin granules and the appearance of dense granular bodies.

Pancreatic A cells of the lizardVaranus niloticus are characterized by the presence of two types of mitochondria: (a) normal, small mitochondria (about 0.4 × 1μm), and (b) giant mitochondria, measuring up to 9 μm in length and 1 μm in diameter. Giant mitochondria show various shapes. Their matrix is filled with tubules, filaments, and dense granules. Transverse sections of tubules are polygonal in shape and about 20 nm in diameter. They are grouped in bundles. The filaments, about 9–10 nm in diameter, are arranged in parallel layers crossing each other at a 57° angle. In a closely related species,Varanus exanthematicus, pancreatic A cells do not show these peculiar features.