Humic Substances. Structural Aspects, and Photophysical, Photochemical and Free Radical Characteristics

Osmoregulatory mechanisms in algae were investigated mainly from a physiological point of view (KAUSS 1977, HELLEBUST 1976). In Porphyra two osmotic agents, i. e. floridoside/isofloridoside (KAUSS 1968) and certain ions, such as K+ and Na+(EPPLEY et al. 1960) are considered for osmotic balance. Accumulations of ions (particularly Na+) in the cytoplasm during osmotic adaptation is improbable, because the activity of enzymes is generally inhibited by high ionic concentrations (FLOWERS et al. 1977).The cellular organization of Porphyra was studied with special emphasis on the development of the vacuolar system under different hyperosmotic conditions. Porphyra was cultivated at various strengths of the culture medium ASP 12 (PROVASOLI 1961) ranging from normal to 6 times concentrated (6x) culture medium. Por electron microscopy freeze fracturing was used (specimens fixed in 2% glutaraldehyde and incubated in 30% glycerol, preparation in a BALZERS BA 360 M apparatus), because chemical fixation gave poor results.

Download Full-text

Molecular Structure of the Outermost Cell Wall Component of Spirillum Serpens

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100079218 ◽

1977 ◽

Vol 35 ◽

pp. 342-343

Author(s):

Wah Chiu ◽

David Grano

Keyword(s):

Molecular Structure ◽

Cell Wall ◽

Outer Membrane ◽

Gel Electrophoresis ◽

Electron Microscopic Examination ◽

Electron Microscopic ◽

Cell Wall Component ◽

Protein Components ◽

Exposure Technique ◽

Structural Aspects

The periodic structure external to the outer membrane of Spirillum serpens VHA has been isolated by similar procedures to those used by Buckmire and Murray (1). From SDS gel electrophoresis, we have found that the isolated fragments contain several protein components, and that the crystalline structure is composed of a glycoprotein component with a molecular weight of ∽ 140,000 daltons (2). Under an electron microscopic examination, we have visualized the hexagonally-packed glycoprotein subunits, as well as the bilayer profile of the outer membrane. In this paper, we will discuss some structural aspects of the crystalline glycoproteins, based on computer-reconstructed images of the external cell wall fragments.The specimens were prepared for electron microscopy in two ways: negatively stained with 1% PTA, and maintained in a frozen-hydrated state (3). The micrographs were taken with a JEM-100B electron microscope with a field emission gun. The minimum exposure technique was essential for imaging the frozen- hydrated specimens.

Download Full-text

7-beam lattice images of (110) oriented Ge

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100108593 ◽

1978 ◽

Vol 36 (1) ◽

pp. 290-291

Author(s):

J.R. Parsons ◽

C.W. Hoelke

Keyword(s):

Image Features ◽

Objective Lens ◽

Lattice Plane ◽

Lattice Image ◽

Crystalline Defects ◽

Transmission Electron ◽

Lattice Images ◽

Electron Microscopes ◽

Structural Aspects ◽

Beam Lattice

The direct imaging of a crystal lattice has intrigued electron microscopists for many years. What is of interest, of course, is the way in which defects perturb their atomic regularity. There are problems, however, when one wishes to relate aperiodic image features to structural aspects of crystalline defects. If the defect is inclined to the foil plane and if, as is the case with present 100 kV transmission electron microscopes, the objective lens is not perfect, then terminating fringes and fringe bending seen in the image cannot be related in a simple way to lattice plane geometry in the specimen (1).The purpose of the present work was to devise an experimental test which could be used to confirm, or not, the existence of a one-to-one correspondence between lattice image and specimen structure over the desired range of specimen spacings. Through a study of computed images the following test emerged.

Download Full-text

Structural aspects of tracheary element differentiation in suspension cultures of Zinnia elegans

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100155815 ◽

1989 ◽

Vol 47 ◽

pp. 768-769

Author(s):

C. H. Haigler ◽

A. W. Roberts

Keyword(s):

Tracheary Element ◽

Vesicle Fusion ◽

Zinnia Elegans ◽

Cellulose Synthesis ◽

Tracheary Elements ◽

Animal Cells ◽

Mesophyll Cells ◽

Fixation Techniques ◽

Localized Patterns ◽

Structural Aspects

Tracheary elements, the water-conducting cells in plants, are characterized by their reinforced walls that became thickened in localized patterns during differentiation (Fig. 1). The synthesis of this localized wall involves abundant secretion of Golgi vesicles that export preformed matrix polysaccharides and putative proteins involved in cellulose synthesis. Since the cells are not growing, some kind of endocytotic process must also occur. Many researchers have commented on where exocytosis occurs in relation to the thickenings (for example, see), but they based their interpretations on chemical fixation techniques that are not likely to provide reliable information about rapid processes such as vesicle fusion. We have used rapid freezing to more accurately assess patterns of vesicle fusion in tracheary elements. We have also determined the localization of calcium, which is known to regulate vesicle fusion in plant and animal cells.Mesophyll cells were obtained from immature first leaves of Zinnia elegans var. Envy (Park Seed Co., Greenwood, S.C.) and cultured as described previously with the following exceptions: (a) concentration of benzylaminopurine in the culture medium was reduced to 0.2 mg/l and myoinositol was eliminated; and (b) 1.75ml cultures were incubated in 22 x 90mm shell vials with 112rpm rotary shaking. Cells that were actively involved in differentiation were harvested and frozen in solidifying Freon as described previously. Fractures occurred preferentially at the cell/planchet interface, which allowed us to find some excellently-preserved cells in the replicas. Other differentiating cells were incubated for 20-30 min in 10(μM CTC (Sigma), an antibiotic that fluoresces in the presence of membrane-sequestered calcium. They were observed in an Olympus BH-2 microscope equipped for epi-fluorescence (violet filter package and additional Zeiss KP560 barrier filter to block chlorophyll autofluorescence).

Download Full-text

Potentiation of bromotrichloromethane hepatotoxicity in male rats exposed to 10 ppm dietary chlordecone: Electron Microscopic and biochemical study

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100158972 ◽

1990 ◽

Vol 48 (3) ◽

pp. 284-285

Author(s):

O. M. Faroon ◽

R. W. Henry ◽

M. G. Soni ◽

H. M. Mehendale

Keyword(s):

Free Radical ◽

Biochemical Study ◽

Prior Exposure ◽

Male Rats ◽

Cellular Injury ◽

Low Doses ◽

Mixed Function Oxidase ◽

Electron Microscopic ◽

Potent Inducer ◽

Cellular Energy

Previous work has shown that mirex undergoes photolytic dechlorination to chlordecone (CD) (KeponeR) in the environment. Much work has shown that prior exposure to nontoxic levels of CD causes potentiation of hepatotoxicity and lethality of CCl4, BrCCl3 and other halomethane compounds. Potentiation of bromotrichloromethane hepatotoxicity has been associated with compounds that stimulate the activity of hepatic mixed-function oxidase (MFO). An increase in the metabolism of halomethane by the MFO to a free radical initiates peroxidative decomposition of membranal lipids ending in massive cellular injury. However, not all MFO inducers potentiate BrCCl3 hepatotoxicity. Potentiation by much larger doses of phenobarbital is minimal and th at by a more potent inducer of MFO, mirex, is negligible at low doses. We suggest that the CD and bromotrichloromethane interaction results in a depletion of cellular energy and thereby reducing the cellular ability to undergo mitosis.

Download Full-text