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J C Tu

Publications and source records attributed to J C Tu.

30 records · Page 2Linked to original sources
PubMed1978

Plasma membrane of Phycomyces: sequential changes in the structure during spore formation.

The plasma membrane of sporangiospores (spores) of Phycomyces blakeleeanus has distinct structural features that distinguish it from the plasma membrane of the sporangiophores. The plasma membrane of the spores is, however, derived from that of the sporangiophore. A study of sequential development of spores shows that the mass of cytoplasm in a sporangial initial is cleavaged by proliferation and subsequent anastomosis and membrane fusion of the clevage vesicles. The plasma membrane of the cleavage vesicles has a reversed curvature (inside out) to that of the sporangial plasma membrane. Otherwise, the distribution of intercalated membranous particles (Imp) on the fractured faces is similar to that of the plasma membrane of the sporangium. Lather, as a result of fusion of cleavage vesicles, curvature of the plasma membrane in the spore initials returns to their original state. In the processes of spore maturation, a new type of structural feature appears in the plasma membrane, which is not present either in the plasma membrane of spore initials or in the plasma membrane of sporangiophores or mycelia. This feature often is seen as large particles (30--35 nm) which are randomly distributed on the exoplasmic face (EF) with corresponding depressions on the plasmic half (PF) in freeze-fractured replicas. They increase in number with increasing spore maturity. These particles are, in fact, the inward protrusions of the plasma membrane of the spore. A change in the number of 5--8 nm intramembranous particles on the fractured faces is also noted during spor maturation, with an increase on the EF face and a corresponding decrease on the PF face. This alteration may result from vertical movement of Imp or from a change in the fracture plane as a consequence of alteration in the lipid content during maturation.

Cell Membrane↗
PubMed1977

The significance of cAMP induced alterations in the cellular structure of Phycomyces.

Effect of cyclic AMP (cAMP) on Phycomyces blakesleeanus was studied by growing sporangiospores on glucose-asparagine agar or liquid medium containing three different levels of cAMP (10, 20 and 40 micronM) in addition to the control (no cAMP added). The response of Phycomyces to the exogenous cAMP concentration in the medium is as follows: (1) the time required for germ tube emergence is reduced; (2) the diameter of the mycelium is increased (sometimes more than 10 times) and frequency of branching is also increased; (3) the cell wall of the mycelium is thickened (in some cases more than 5 times); (4) the glycogen in the cytoplasm is decreased as visualized in thin sections and also demonstrated in biochemical quantitation; and (5) the distribution of intercalated membranous particles (Imp) on plasma membrane is altered and this can be easily detected in freeze-fractured replica. Such a change in Imp is seen in the formation of small clusters of aggregated particles on the plasmic half (PF) and craters on the complementary exoplasmic half (EF) of the plasma membrane. Although the mechanism of cAMP action requires further exploration, it is possible that the addition of cAMP to the culture medium leads to degradation of glycogen and enhancement of chitin synthesis since the cell wall is largely composed of chitin. The alteration in Imp may be related to a change in the activity of chitin synthetase which is a plasma membrane-bound enzyme.

Cyclic AMP↗
PubMed1976

The formation of sporangiospores in Phycomyces.

The multinucleate state of the vegetative spores of Phycomyces blakesleeanus arises as a consequence of cleavage of cytoplasm containing a variable number (1-6) of pre-existing nuclei. No nuclear division or incorporation of 3H-thymidine was detected during maturation of the spores.

Cell Nucleus↗
PubMed1975

Functional characterization of types of plasma membranes in cerebral cortex.

The cerebral cortex of normal oxygenated and of asphyxiated mice has been studied by freeze-fracturing technique with a twofold purpose. First, to investigate changes, if any, in the molecular organization of the plasma membrane of any specific cell type(s) that could be correlated with permeability changes thought to take place as a consequence of asphyxiation. Secondly, to attempt characterization of plasma membranes on the basis of the organization of their fractured faces. The decrease in the extracellular material in asphyxiated cerebral cortex seen in electron micrographs of thin sections could not be correlated with change(s), if any, in the molecular organization of the plasma membrane of any particular cell type. Plasma membranes of various types could be characterized on the basis of the arrangement of particles on the fractured faces. Some of these types correspond to identifiable cell processes, while others have not yet been identified with certainty. Fusion of synaptic vesicles with the presynaptic membrane is mediated through clustering of 100-150 A membrane-associated particles.

Animals↗
PubMed1975

Structural similarity of the membrane envelopes of rhizobial bacteroids and the host plasma membrane as revealed by freeze-fracturing.

The freeze-fracture technique was used to study the host plasma membrane and the membrane envelope of bacteroids in rhizobial root nodules of three host-rhizobium combinations. In all three combinations studied, the membrane envelopes of bacteroids are structurally similar to their host plasma membrane. However, the membrane appears to be reversed, because the number and arrangement of particles in the outer fractured face (face A, concave) and in the inner fractured face (face B, convex) of the host plasma membrane are seen, respectively, in the inner fractured face (face B, convex) and in the outer fractured face (face A, concave) of the membrane envelope of the bacteroids at an early stage. This reversion of the membrane surface is consistent with the hypothesis that the membrane envelopes of bacteroids are derived from the host plasma membrane during endocytotic engulfment.

Cell Membrane↗
PubMed1974

Relationship between the membrane envelope of rhizobial bacteroids and the plasma membrane of the host cell as demonstrated by histochemical localization of adenyl cyclase.

By using adenyl cyclase as a marker enzyme, the relationship between the membrane envelope of the bacteroids of rhizobia and the plasma membrane of the host cell was demonstrated histochemically. Electron-dense deposits were found on the outer surface of the plasma membrane of the host cell and on the inner surface of the membrane envelopes of the bacteroids, but not in vacuole membranes, endoplasmic reticula, Golgi apparatus, and mitochondrial membranes. The results suggest that the membrane envelopes of the bacteroids are closely related to the host plasma membrane, and that entry of the bacteroids into the cytoplasm is in a manner similar to endocytosis.

Adenylyl Cyclases↗