Update of the 1972 Singer-Nicolson Fluid-Mosaic Model of Membrane Structure

In the investigation of the molecular organization of cell membranes it is often supposed that lipid molecules are arranged in a bimolecular film. X-ray diffraction data obtained in a direction perpendicular to the plane of suitably layered membrane systems have generally been interpreted in accord with such a model of the membrane structure. The present studies were begun in order to determine whether selected area electron diffraction would provide a tool of sufficient sensitivity to permit investigation of the degree of intermolecular order within lipid films. The ultimate objective would then be to apply the method to single fragments of cell membrane material in order to obtain data complementary to the transverse data obtainable by x-ray diffraction.

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Cellulose Acetate Reverse Osmosis Membrane Structure

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100095893 ◽

1972 ◽

Vol 30 ◽

pp. 528-529

Author(s):

H. K. Plummer ◽

E. Eichen ◽

C. D. Melvin

Keyword(s):

Cellulose Acetate ◽

Reverse Osmosis ◽

Membrane Structure ◽

Freeze Drying ◽

Dense Layer ◽

Water Removal ◽

Reverse Osmosis Membrane ◽

Correct Interpretation ◽

Electron Image ◽

Scanning Electron

Much of the work reported in the literature on cellulose acetate reverse osmosis membranes has raised new and important questions with regard to the dense or “active” layer of these membranes. Several thickness values and structures have been attributed to the dense layer. To ensure the correct interpretation of the cellulose acetate structure thirteen different preparative techniques have been used in this investigation. These thirteen methods included various combinations of water substitution, freeze drying, freeze sectioning, fracturing, embedding, and microtomy techniques with both transmission and scanning electron microscope observations.It was observed that several factors can cause a distortion of the structure during sample preparation. The most obvious problem of water removal can cause swelling, shrinking, and folds. Improper removal of embedding materials, when used, can cause a loss of electron image contrast and, or structure which could hinder interpretation.

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Warm and freeze-fracture of cotton seed radicles

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100129206 ◽

1987 ◽

Vol 45 ◽

pp. 984-985

Author(s):

E. L. Vigil ◽

E. F. Erbe

Keyword(s):

Thin Film ◽

Water Vapor ◽

Fracture Surface ◽

Membrane Structure ◽

Room Temperature ◽

Freeze Fracture ◽

Longitudinal Axis ◽

Fracture Plane ◽

Cotton Seeds ◽

Condensed Water

In cotton seeds the radicle has 12% moisture content which makes it possible to prepare freeze-fracture replicas without fixation or cryoprotection. For this study we have examined replicas of unfixed radicle tissue fractured at room temperature to obtain data on organelle and membrane structure.Excised radicles from seeds of cotton (Gossyplum hirsutum L. M-8) were fractured at room temperature along the longitudinal axis. The fracture was initiated by spliting the basal end of the excised radicle with a razor. This procedure produced a fracture through the tissue along an unknown fracture plane. The warm fractured radicle halves were placed on a thin film of 100% glycerol on a flat brass cap with fracture surface up. The cap was rapidly plunged into liquid nitrogen and transferred to a freeze- etch unit. The sample was etched for 3 min at -95°C to remove any condensed water vapor and then cooled to -150°C for platinum/carbon evaporation.

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The ultrastructure of the double membrane-bound bodies and endoplasmic reticulum in serial sections of wheat spot mosaic-affected wheat plants

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100161023 ◽

1990 ◽

Vol 48 (3) ◽

pp. 694-695

Author(s):

M. H. Chen ◽

C. Hiruki

Keyword(s):

Endoplasmic Reticulum ◽

High Resolution ◽

Membrane Structure ◽

Mosaic Disease ◽

Serial Sections ◽

Thin Sections ◽

Double Membrane ◽

Southern Alberta ◽

Membrane Bound ◽

Scanning Em

Wheat spot mosaic disease was first discovered in southern Alberta, Canada, in 1956. A hitherto unidentified disease-causing agent, transmitted by the eriophyid mite, caused chlorosis, stunting and finally severe necrosis resulting in the death of the affected plants. Double membrane-bound bodies (DMBB), 0.1-0.2 μm in diameter were found to be associated with the disease.Young tissues of leaf and root from 4-wk-old infected wheat plants were fixed, dehydrated, and embedded in Spurr’s resin. Serial sections were collected on slot copper grids and stained. The thin sections were then examined with a Hitachi H-7000 TEM at 75 kV. The membrane structure of the DMBBs was studied by numbering them individually and tracing along the sections to see any physical connection with endoplasmic reticulum (ER) membranes. For high resolution scanning EM, a modification of Tanaka’s method was used. The specimens were examined with a Hitachi Model S-570 SEM in its high resolution mode at 20 kV.

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