scholarly journals Correlation between the freeze fracture appearance and polypeptide composition of thylakoid membranes in barley

1977 ◽  
Vol 42 (6) ◽  
pp. 499-516 ◽  
Author(s):  
Otto Machold ◽  
David J. Simpson ◽  
Gunilla Høyer-Hansen
Keyword(s):  
Freeze Fracture ◽  
Thylakoid Membranes ◽  
Polypeptide Composition ◽  
Fracture Appearance

Freeze-fracture architecture and polypeptide composition of thylakoid membranes from euploid Ricinus cells

1981 ◽  
Vol 52 (1) ◽  
pp. 167-181
Author(s):  
M.P. Timko ◽  
R.E. Triemer ◽  
A.C. Vasconcelos
Keyword(s):  
Ricinus Communis ◽  
Relative Proportion ◽  
Freeze Fracture ◽  
Nuclear Genome ◽  
Electron Microscopic Examination ◽  
Thylakoid Membranes ◽  
Polypeptide Composition ◽  
Electron Microscopic ◽  
Size Category ◽  
Ploidy Levels

The freeze-fracture architecture and polypeptide composition of thylakoid membranes of euploid cells of Ricinus communis L. were examined. Electron microscopic examination of the chloroplasts of 1N 2N and 4N cells revealed little variation in the size of chloroplasts, lamellar structure and internal organization of plastids, despite increases in plastid numbers per cell observed to accompany the increase in nuclear ploidy. Thylakoid membranes from euploid cells were also similar in their freeze-fracture morphology. Two basic types of intramembranous particles were observed on the fracture faces of thylakoid membranes of euploid cells. The endoplasmic fracture (EF) face of experimentally unstacked thylakoid membranes of 1N, 2N and 4N cells contain 2 size categories of particles (115-121 A and 164–166 A), whereas the protoplasmic fracture (PF) face of these membranes contain a single size category of particles (85-88 A). The distribution and size of the EF- and PF-face particles were found to be similar among membranes from cells of the 3 ploidy levels. Analysis of the polypeptide composition of thylakoid membranes from 1N, 2N and 4N cells revealed no difference in the relative proportion of the constituent polypeptides of these membranes. The possible factors involved in the regulation of the development of thylakoid structure and composition in the presence of altered nuclear genome size are discussed.

The structure and function of grana-free thylakoid membranes in gerontoplasts of senescent leaves of vicia faba l.

1988 ◽  
Vol 43 (1-2) ◽  
pp. 149-154 ◽  
Author(s):  
H. Oskar Schmidt
Keyword(s):  
Vicia Faba ◽  
Thylakoid Membranes ◽  
Photochemical Activity ◽  
Structure And Function ◽  
Polypeptide Composition ◽  
Light Harvesting Complex ◽  
Vicia Faba L ◽  
Light Protection ◽  
Flotation Method ◽  
And Function

In the course of yellowing (senescence) the leaves of Vicia faba L. lose 95% of their chlorophyll. Gerontoplasts develop from chloroplasts and aggregate with the pycnotic mitochondria and the cell nucleus in the senescent cells (organelle aggregation). The gerontoplasts contain only a few, unstacked thylakoid membranes but a large number of carotinoid-containing plastoglobuli, which after the degration of chlorophyll presumably assume the light protection of the cells. The thylakoid membranes of the gerontoplasts were isolated by means of a flotation method. Their polypeptide composition is characterized by a high proportion of light-harvesting complex. Evidence of relatively high photochemical activity shows that functional thylakoid membranes are present in the premortal senescence state of leaves and this suggests that there is functional compartmentation of the hydrolytic processes in this stage of the leaves’ development

Changes of the Polypeptide Composition in Thylakoid Membranes during Differentiation

1990 ◽  
Vol 45 (3-4) ◽  
pp. 253-257 ◽  
Author(s):  
Magdolna Droppa ◽  
Jiri Masojidek ◽  
Gábor Horváth
Keyword(s):  
Molecular Weight ◽  
Chloroplast Development ◽  
Early Stage ◽  
Relative Concentration ◽  
Thylakoid Membranes ◽  
Low Molecular Weight ◽  
Polypeptide Composition ◽  
Lhc Ii

Changes in membrane polypeptide composition during greening of etiolated maize were investigated to confirm the existence of the developmental polypeptides of 12 - 15 kDa described recently in virescent soybean mutant [M. Droppa, M. L. Ghirardi, G. Horváth, and A. Melis, Biochim. Biophys. Acta 932, 138 - 145 (1988)]. These low molecular weight polypeptides were the most abundant proteins at the early stage of greening, but were largely absent from fully developed thylakoids. During greening the relative concentration of the 12-15 kDa polypeptides were inversely proportional to that of LHC II, suggesting a role of these polypeptides in the assembly of the LHC II and/or chloroplast development.

scholarly journals Freeze-fracture studies of nexuses between smooth muscle cells. Close relationship to sarcoplasmic reticulum.

1977 ◽  
Vol 72 (1) ◽  
pp. 26-34 ◽  
Author(s):  
G N Fry ◽  
C E Devine ◽  
G Burnstock
Keyword(s):  
Smooth Muscle ◽  
Sarcoplasmic Reticulum ◽  
Guinea Pig ◽  
Hexagonal Lattice ◽  
Freeze Fracture ◽  
Minimum Size ◽  
Mouse Vas Deferens ◽  
Chicken Gizzard ◽  
Close Relationship ◽  
Fracture Appearance

The freeze-fracture appearance of the nexus was compared in the smooth muscle of guinea pig sphincter pupillac, portal vein, pulmonary artery, taenia coli, uretzr, and vas diferens, mouse vas deferens, chicken gizzard and anterior mesenteric artery, and toad stomach. Nexuses are particularly numerous in the guinea pig sphincter pupillae; they are usually oval and their average area is 0.15 mum2, although some as large as 0.6 mum2 were seen. Small aggregations of particles were observed which would not be recognizable as nexuses in thin section. What constitutes the minimum size of a nexus is discussed. It is estimated that the number of nexuses per cell in this preparation is of the order of tens rather than hundreds. All nexuses examined had 6-9-nm particles in the PF face, with corresponding 3-4-nm pits on the EF face forming a polygonal tending towards a hexagonal lattice. The nexuses are arranged in rows parallel to the main axis of the cell, usually alternating with longitudinal rows of plasmalemmal vesicles. Many nexuses in the guinea pig sphincter pupillae, chicken gizzard, and toad stomach show a close relationship with sarcoplasmic reticulum. The possibility that this may have some role in current flow across this specialized junction is discussed.

scholarly journals Membrane particle changes attending the acrosome reaction in guinea pig spermatozoa

1977 ◽  
Vol 74 (2) ◽  
pp. 561-577 ◽  
Author(s):  
DS Friend ◽  
L Orci ◽  
A Perrelet ◽  
R Yanagimachi
Keyword(s):  
Plasma Membrane ◽  
Guinea Pig ◽  
Acrosome Reaction ◽  
Plasma Membranes ◽  
Freeze Fracture ◽  
Phosphatidylcholine Liposomes ◽  
Acrosomal Membrane ◽  
Large Particles ◽  
Fracture Appearance ◽  
Preparatory Stage

To examine the freeze-fracture appearance of membrane alterations accompanying the preparation of sperm membranes for fusions-the first preparatory stage occurring before physiological release of the acrosomal content, the second afterward-we induced the acrosome reaction in capacitated guinea pig spermatozoa by adding calcium to the mixture. The most common features observed before fusion of the acrosomal and plasma membranes were the deletion of fibrillar intramembranous particles from the E-fracture faces of both membranes, and the clearance of globular particles from the P face of the plasma membrane-events taking place near the terminus of the equatorial segment. Large particles, >12nm, remained not far from the cleared E-face patches. The P face of the outer acrosomal membrane is virtually clear from the outset. In addition, when fusion was completed, occasional double lines of large particles transiently embossed the P face of the plasma membrane (postacrosomal) side of the fusion zone. Behind the line of fusion, another series of particle-cleared foci emerged. We interpreted these postfusion membrane clearances as a second adaptation for sperm-egg interaction. Induction of the acrosome reaction in media containing phosphatidylcholine liposomes resulted in their apparent attachment, incorporation, or exchange in both the originally and secondarily cleared regions. Our observations support the concepts that membranes become receptive to union at particle- deficient interfaces, and that the physiologically created barren areas in freeze-fracture replicas may herald incipient membrane fusion.

Ultrastructural changes in chloroplasts resulting from fluctuations in NaCl concentration: freeze-fracture of thylakoid membranes in Dunaliella salina

1975 ◽  
Vol 18 (2) ◽  
pp. 287-299 ◽  
Author(s):  
A.O. Pfeifhofer ◽  
J.C. Belton
Keyword(s):  
Salt Concentration ◽  
Dunaliella Salina ◽  
Unit Area ◽  
Morphological Changes ◽  
Membrane Surface ◽  
Freeze Fracture ◽  
Thylakoid Membranes ◽  
Ultrastructural Changes ◽  
Thin Sections ◽  
Number Of Particles

The structure of chloroplasts isolated from Dunaliella salina has been studied with respect to changing concentrations of sodium chloride in the culture medium. Freeze-fracture replicas and thin sections of intact chloroplasts do not exhibit any noticeable changes in structure at concentrations ranging between 3.5 and 25% NaCl. Chloroplasts isolated from algal cells that have been acclimatized to the higher salt concentration show a change in the thylakoid membranes. The thylakoid membranes appear compressed over a major portion of the membrane surface, with only the end of the thylakoid membranes unappressed. The number of particles per unit area on the B face is also altered by the salt concentration. The chloroplasts acclimatized to 25% NaCl have about 3 times the number of particles per unit area on a B face of end-membranes as on a comparable face of thylakoid membranes acclimatized to low (3.5% NaCl) salt concentration. These morphological changes can be reversed if the chloroplasts acclimatized to high or low salt concentrations are returned to a medium of different salt concentration prior to freeze-fracturing.

scholarly journals Gap junction dynamics: reversible effects of hydrogen ions.

1980 ◽  
Vol 87 (3) ◽  
pp. 719-727 ◽  
Author(s):  
C Peracchia ◽  
L L Peracchia
Keyword(s):  
Gap Junctions ◽  
Divalent Cations ◽  
Structural Characteristics ◽  
Freeze Fracture ◽  
Low Ph ◽  
Hydrogen Ions ◽  
Intact Cells ◽  
Lens Fibers ◽  
Fracture Appearance ◽  
Particle Packings

Reversible crystallization of intramembrane particle packings is induced in gap junctions isolated from calf lens fibers by exposure to 3 x 10(-7) M or higher [H+] (pH 6.5 or lower). The changes from disordered to crystalline particle packings induced by low pH are similar to those produced in junctions of intact cells by uncoupling treatments, indicating that H+, like divalent cations, could be an uncoupling agent. The freeze-fracture appearance of both control and low pH-treated gap junctions is not altered by glutaraldehyde fixation and cryoprotective treatment, as suggested by experiments in which gap junctions of both intact cells and isolated fractions are freeze-fractured after rapid freezing to liquid N2 temperature according to Heuser et al. (13). In junctions exposed to low pH, the particles most often form orthogonal and rhombic arrays, frequently fused with each other. A number of structural characteristics of these arrays suggest that the particles of lens fiber gap junctions may be shaped as tetrameres.

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