Electrical Properties and Ultrastructure of Mycoplasma Membranes

Mycoplasma, in particular species laidlawii and gallisepticum, are found to have a very small, low frequency conductivity as would be predicted by the dielectric model for bacteria and their apparent lack of cell wall structure. Membrane capacitance values for the two organisms are both about 0.9 μF/cm², although electron micrographs show that the membrane of M. gallisepticum is 20-40 A thicker than that of M. laidlawii.     

Male external genitalia and systematic relationships of the Japanese macaque (Macaca fuscata Blyth, 1875)

Penial morphology was studied in six preserved specimens of the Japanese macaque,Macaca fuscata. Structure of the glans penis and baculum inM. fuscata is essentially similar to that in the rhesus macaque,M. mulatta. With age the skin of the penis inM. fuscata apparently becomes progressively more darkly and extensively pigmented, and the baculum becomes progressively longer. One immature specimen examined, with penial skin unpigmented and baculum cartilaginous, appears to be abnormally retarded in penial development. Penial morphology suggests that the allopatric speciesM. fuscata, M. mulatta, M. cyclopis, andM. fascicularis constitute a closely interrelated group. Contrary to a previous report, there is no evidence that penial morphology inM. fuscata is transitional to that inM. radiata andM. sinica. InM. fuscata, M. mulatta, andM. fascicularis, latitudinal variation of body size and relative tail length conforms toBergmann's rule andAllen's rule; external proportions in three specimens ofM. cyclopis only partly conform to this pattern.     

THE FINE STRUCTURE OF CHONDROCOCCUS COLUMNARIS : I. Structure and Formation of Mesosomes

Cells of Chondrococcus columnaris were sectioned and examined in the electron microscope after fixation by two different methods. After fixation with osmium tetroxide alone, the surface layers of the cells consisted of a plasma membrane, a dense layer (mucopeptide layer), and an outer unit membrane. The outer membrane appeared distorted and was widely separated from the rest of the cell. The intracytoplasmic membranes (mesosomes) appeared as convoluted tubules packaged up within the cytoplasm by a unit membrane. The unit membrane surrounding the tubules was continuous with the plasma membrane. When the cells were fixed with glutaraldehyde prior to fixation with osmium tetroxide, the outer membrane was not distorted and separated from the rest of the cell, structural elements (peripheral fibrils) were seen situated between the outer membrane and dense layer, and the mesosomes appeared as highly organized structures produced by the invagination and proliferation of the plasma membrane. The mesosomes were made up of a series of compound membranes bounded by unit membranes. The compound membranes were formed by the union of two unit membranes along their cytoplasmic surfaces.     

THE FINE STRUCTURE OF CHONDROCOCCUS COLUMNARIS : II. Structure and Formation of Rhapidosomes

When cells of C. columnaris were broken open, treated with PTA, and examined in the electron microscope, tubular structures (rhapidosomes) were present in the preparations. The rhapidosomes are approximately 300 A in diameter. Their length varies from about 500 to about 15,000 A. An axial hole which runs the length of the rhapidosomes appears to widen and narrow with a regular periodicity. End-on views of short segments of rhapidosomes revealed the presence of subunits around their outside peripheries. The results of studies of lysed cells and of sectioned cells indicate that the rhapidosomes are produced during the disintegration of cells. It seems likely that the compound membranes of the mesosomes break down to give rise to the tubular structures. The mesosomal origin of rhapidosomes is postulated only for the rhapidosomes of C. columnaris, since the origin of rhapidosomes from other organisms was not investigated during this study. The rhapidosomes of C. columnaris may be unrelated to those of S. grandis, S. myxococcoides, A. violaceum, and Sorangium 495, since there was a difference in the details of fine structure between rhapidosomes from C. columnaris and those found in the other four organisms.     

Filamentous Cells of Escherichia coli Formed in the Presence of Mitomycin

The effects of mitomycin C on cell elongation of Escherichia coli B were studied. Filament formation was most marked in cultures treated with a moderate level (1 mug/ml) of the antibiotic, becoming less obvious at higher levels (10 mug/ml). Cells treated with a bacteriostatic concentration (0.1 mug/ml or less) of mitomycin C were also significantly elongated. The filamentous or elongated cells appeared to lack septa, since their spheroplasts were considerably larger than those formed from normal cells. The appearance of empty spheres also indicated some defects in the surfaces of the filamentous cells. Electron micrographs of the filaments revealed a characteristic difference in the arrangement of the nuclei in the filaments formed in the presence of low (0.1 mug/ml) and high (5 mug/ml) concentrations of mitomycin C. The filaments formed by the low level of mitomycin C had normal well-defined nuclear bodies distributed along the long axis, whereas those formed by the elevated level of the antibiotic contained smaller nuclei. The latter were characteristically confined to the center of the cells and did not extend out to the tips of the filaments.     

THE FINE STRUCTURE OF ACOUSTIC GANGLIA IN THE RAT

Nerve cell bodies in the spiral and vestibular ganglia of the adult rat are surrounded by thin (about ten lamellae) myelin sheaths which differ in several respects from typical axonal myelin. In some instances lamellae surrounding perikarya appear as typical major dense lines, and in others as thin Schwann cell sheets in which cytoplasm persists. Discontinuities and irregularities appear in the structure of perikaryal myelin. Lamellae may terminate anywhere within the sheaths; they may bifurcate; they may reverse their direction; or they may merge with each other. The number of lamellae varies from one part of a sheath to another. In addition, the myelin of a single perikaryal sheath may receive contributions from more than one Schwann cell, which overlap and interleave with each other. The ganglion cells are of two types: those which are densely packed with the usual cytoplasmic organelles but have few neurofilaments (granular neurons), and those which exhibit large areas containing few organelles but have a high concentration of neurofilaments (filamented neurons). The latter cell type is ensheathed by myelin which is generally more compact that that surrounding the former. The formation and the physiologic significance of perikaryal myelin are discussed.     

SUBSURFACE CISTERNS AND THEIR RELATIONSHIP TO THE NEURONAL PLASMA MEMBRANE

Subsurface cisterns (SSC's) are large, flattened, membrane-limited vesicles which are very closely apposed to the inner aspect of the plasma membranes of nerve cell bodies and the proximal parts of their processes. They occur in a variety of vertebrate and invertebrate neurons of both the peripheral and central nervous systems, but not in the surrounding supporting cells. SSC's are sheet-like in configuration, having a luminal depth which may be less than 100 A and a breadth which may be as much as several microns. They are separated from the plasmalemma by a light zone of ~50 to 80 A which sometimes contains a faint intermediate line. Flattened, agranular cisterns resembling SSC's, but structurally distinct from both typical granular endoplasmic reticulum (ER) and from Golgi membranes, also occur deep in the cytoplasm of neurons. It is suggested that membranes which are closely apposed may interact, resulting in alterations in their respective properties. The patches of neuronal plasmalemma associated with subsurface cisterns may, therefore, have special properties because of this association, resulting in a non-uniform neuronal surface. The possible significance of SSC's in relation to neuronal electrophysiology and metabolism is discussed.     

A bibliography on howler monkeys (Alouatta sp.)

Reports dealing with howler monkeys since1900 have been assembled in the present bibliography. The references marked with(R) have been taken verbatim from Ruch's Bibliographia Primatologica. Papers identified by^* deal more extensively withAlouatta.     

Gibberellin Effect on Tryptophan Metabolism, Auxin Destruction, and Abscission in Coleus

Application of gibberellic acid (GA) to the apical region of the stem enhances ¹⁴CO₂ release from tryptophan-l-¹⁴C in cell free preparations of the apical region. Although GA when applied to the apical region markedly accelerates abscission rates of debladed petioles at the 4th node, the enhancement effect on tryptophan metabolism appears to be restricted to the apical bud region. The increased levels of diffusible auxin in Coleus stems, observed earlier by Muir and Valdovinos (1965), appear to be due to the GA effect on auxin precursor conversion rather than to an altered rate of auxin destruction. GA pre-treatment does not significantly alter destruction rates of auxin in the stem tissue. This is demonstrated by the release of ¹⁴CO₂ from IAA-1-¹⁴C by sections of internode tissue. While a multiple deblading pattern retards abscission of debladed petioles considerably, application of GA to debladed petioles at the basal region of the stem restores the normal rates of abscission at debladed distal nodes. No significant change in the abscission rates at treated nodes is observed. The GA effect on abscission at distal nodes is attributed to the effect of the growth substance on auxin precursor conversion in the apical region. In these experiments, as in the case of plants treated in the apical region with GA, auxin destruction rates in the stem are not altered significantly.