scholarly journals Studies in Translocation II. Submicroscopic Anatomy of The Phloem

1961 ◽  
Vol 14 (4) ◽  
pp. 506 ◽  
Author(s):  
Margaret Duloy FV Mercer ◽  
Nele Rathgeber
Keyword(s):  
Aqueous Solution ◽  
Cucurbita Pepo ◽  
Sieve Element ◽  
Sieve Plate ◽  
Side Walls ◽  
Mature Sieve Element

Electron.microscope studies have been made of the cells of the phloem and pericyclic ground parenchyma of the stem of Cucurbita pepo (Duchesne). The mature sieve element contains no cytoplasm, either on the side walls or at the sieve plate, such as occurs in other cells. The walls are lined with a parietal layer which encloses an aqueous solution in which are dispersed fibrils of slime.

Development of sieve tubes in Acer pseudoplatanus

1966 ◽  
Vol 163 (993) ◽  
pp. 524-537 ◽  
Keyword(s):  
Close Association ◽  
Wall Material ◽  
Acer Pseudoplatanus ◽  
Sieve Plate ◽  
Mature Cell ◽  
Golgi Bodies ◽  
Functional Relationships ◽  
Sieve Tubes ◽  
Laminar Material ◽  
Mature Sieve Element

Observations on the development of the sieve-plate pores of Acer pseudoplatanus have enabled five stages in the differentiation of the cell to be recognized. The functional relationships of the endoplasmic reticulum to the formation of the sieve plate and its close association with other organelles of the cell during development have been described in detail. During differentiation slime bodies are formed and these disaggregate to form the fibrillar material present in the lumen of the mature cell. It is probable that the fibres found in the slime body arise from granular bodies which may consist of ribosomes, seen within the organelles. The granules are thought to form the fibrils which are linear subunits of the fibres of the slime body and the sieve-plate pores. An account is given of the degeneration of the nucleus and the changes in the fine structure of the mitochondria and plastids which accompany the differentiation of a cambial initial into a mature sieve element. The formation of laminar material and other inclusions found in the mature cell is also described. Autoradiographic techniques have been used to show the function of the Golgi bodies and their associated vesicles in the development of the cell wall and also to indicate that some of the callose formed at the sieve plate is deposited after the general formation of wall material. This latter observation lends support to the view that callose is deposited at the sieve plate in response to wounding of the tissue.

scholarly journals TUBULAR AND FIBRILLAR COMPONENTS OF MATURE AND DIFFERENTIATING SIEVE ELEMENTS

1967 ◽  
Vol 34 (3) ◽  
pp. 801-815 ◽  
Author(s):  
James Cronshaw ◽  
Katherine Esau
Keyword(s):  
Light And Electron Microscopy ◽  
Protein Body ◽  
Sieve Element ◽  
Protein Component ◽  
Sieve Plate ◽  
Sieve Elements ◽  
P Protein ◽  
Ontogenetic Study ◽  
P2 Protein ◽  
Fibrillar Component

An ontogenetic study of the sieve element protoplast of Nicotiana tabacum L. by light and electron microscopy has shown that the P-protein component (slime) arises as small groups of tubules in the cytoplasm. These subsequently enlarge to form comparatively large compact masses of 231 ± 2.5 (SE)A (n = 121) tubules, the P-protein bodies. During subsequent differentiation of the sieve element, the P-protein body disaggregates and the tubules become dispersed throughout the cell. This disaggregation occurs at about the same stage of differentiation of the sieve elements as the breakdown of the tonoplast and nucleus. Later, the tubules of P-protein are reorganized into smaller striated 149 ± 4.5 (SE)A (n = 43) fibrils which are characteristic of the mature sieve elements. The tubular P-protein component has been designated P1-protein and the striated fibrillar component P2-protein. In fixed material, the sieve-plate pores of mature sieve elements are filled with proteinaceous material which frays out into the cytoplasm as striated fibrils of P2-protein. Our observations are compatible with the view that the contents of contiguous mature sieve elements, including the P-protein, are continuous through the sieve-plate pores and that fixing solutions denature the proteins in the pores. They are converted into the electron-opaque material filling the pores.

Nuclear crystalloids in sieve elements of Boraginaceae: a protein digestion study

1983 ◽  
Vol 64 (1) ◽  
pp. 37-47
Author(s):  
J. Thorsch ◽  
K. Esau
Keyword(s):  
Proteolytic Enzymes ◽  
Differential Response ◽  
Sieve Element ◽  
Enzyme Digestion ◽  
The Other ◽  
Sieve Plate ◽  
Protein Digestion ◽  
Sieve Elements ◽  
P Protein ◽  
Parallel Arrangement

Nuclear crystalloids have been found in sieve elements of several Boraginaceae. Nuclei of differentiating sieve elements of Echium and other genera except Amsinckia contain one or more crystalloids composed of thin rods densely packed in parallel arrangement. After the nuclei disintegrate in the maturing sieve element the crystalloids are released into the cell lumen where they persist intact. In Amsinckia the crystalloid consists of two components: a dense component, similar to the crystalloid in the other genera and a loosely arranged paracrystalline component. The proteinaceous nature of the nuclear crystalloids and their possible similarity to P-protein was investigated by enzyme digestion techniques. Three proteolytic enzymes were employed in this study: protease, pepsin and trypsin. Successful digestion of the dense crystalloid in both Echium and Amsinckia was obtained with each enzyme tested. P-protein plugging the sieve plate pores was also digested. The loose component in Amsinckia and the aggregated and dispersed P-protein were not affected by the enzyme digestion procedures. These results seemed to indicate that the density or compactness of the proteinaceous inclusions may play a role in the differential response.

Fine structure of the differentiating sieve elements of Vicia faba

1969 ◽  
Vol 17 (3) ◽  
pp. 441 ◽  
Author(s):  
S Zee
Keyword(s):  
Fine Structure ◽  
Vicia Faba ◽  
Inclusion Bodies ◽  
Close Association ◽  
Membrane System ◽  
Sieve Element ◽  
Sieve Plate ◽  
Starch Granules ◽  
Sieve Elements ◽  
Early Stages

The fine structure of the sieve elements of the primary phloem of the epicotyl of Vicia faba is described. The cytoplasm of the young sieve element contains four distinct forms of "slime" body: amorphous, crystalline, tubular (each tubule measuring about 140 Å in diameter), and short fibrillar (each fibril measuring about 350 Å in diameter). At the very early stages of differentiation, polysome helices are prevalent often in close association with the amorphous but not the other forms of "slime" bodies. At the early stages of development of the sieve element the tubular form of "slime" is closely associated with the endoplasmic reticulum, which suggests their possible origin. The plastids of the sieve element lack a well-developed internal membrane system but contain two characteristic types of inclusion bodies, starch granules and crystalloids identical to those revorted for the secondarv vhloem of the root of Pisum sativum. Mitochondria - remain apparently unchanged throughout sieve element development. Microtubules are present during the early stages of sieve element development but become scarce at later stages. Dictyosomes, coated vesicles, ribosomes, polysomes, and nucleus disappear as the sieve element matures. The fine structure of the sieve plate pore initial is complex. It consists of an outer electron-dense ring ("desmotubule") which encloses a central dark core. The developmental pattern of the sieve plate pore has been traced from the very young to the mature stages.

Structures Formed by Cryoprotective Agents Used in Freezc-Etching

1971 ◽  
Vol 29 ◽  
pp. 448-449
Author(s):  
G. G. Cocks ◽  
C. E. Cluthe
Keyword(s):  
Aqueous Solution ◽  
Polyethylene Oxide ◽  
Liquid Nitrogen Temperature ◽  
Ice Crystals ◽  
Etching Technique ◽  
Structural Constituent ◽  
Cryoprotective Agents ◽  
Quick Freezing ◽  
Freeze Etching ◽  
Fractured Surface

The freeze etching technique is potentially useful for examining dilute solutions or suspensions of macromolecular materials. Quick freezing of aqueous solutions in Freon or propane at or near liquid nitrogen temperature produces relatively large ice crystals and these crystals may damage the structures to be examined. Cryoprotective agents may reduce damage to the specimem, hut their use often results in the formation of a different set of specimem artifacts.In a study of the structure of polyethylene oxide gels glycerol and sucrose were used as cryoprotective agents. The experiments reported here show some of the structures which can appear when these cryoprotective agents are used.Figure 1 shows a fractured surface of a frozen 25% aqueous solution of sucrose. The branches of dendritic ice crystals surrounded hy ice-sucrose eutectic can be seen. When this fractured surface is etched the ice in the dendrites sublimes giving the type of structure shown in Figure 2. The ice-sucrose eutectic etches much more slowly. It is the smooth continuous structural constituent surrounding the branches of the dendrites.

Preparation and characterisation of vanadium pentoxide supported rhodium catalyst

1988 ◽  
Vol 46 ◽  
pp. 946-947
Author(s):  
A. Legrouri
Keyword(s):  
Aqueous Solution ◽  
Thermal Decomposition ◽  
Physicochemical Properties ◽  
Surface Area ◽  
Vanadium Pentoxide ◽  
High Purity ◽  
Gas Adsorption ◽  
Rhodium Catalyst ◽  
Optical Methods ◽  
Reducible Oxides

The industrial importance of metal catalysts supported on reducible oxides has stimulated considerable interest during the last few years. This presentation reports on the study of the physicochemical properties of metallic rhodium supported on vanadium pentoxide (Rh/V2O5). Electron optical methods, in conjunction with other techniques, were used to characterise the catalyst before its use in the hydrogenolysis of butane; a reaction for which Rh metal is known to be among the most active catalysts.V2O5 powder was prepared by thermal decomposition of high purity ammonium metavanadate in air at 400 °C for 2 hours. Previous studies of the microstructure of this compound, by HREM, SEM and gas adsorption, showed it to be non— porous with a very low surface area of 6m2/g3. The metal loading of the catalyst used was lwt%Rh on V2Q5. It was prepared by wet impregnating the support with an aqueous solution of RhCI3.3H2O.

TEM observation of iron oxide pillars in montmorillonite

1990 ◽  
Vol 48 (4) ◽  
pp. 882-883
Author(s):  
H. Mori ◽  
Y. Murata ◽  
H. Yoneyama ◽  
H. Fujita
Keyword(s):  
Aqueous Solution ◽  
Iron Oxide ◽  
Fine Particles ◽  
Aqueous Suspension ◽  
Volume Ratio ◽  
Exchange Capacity ◽  
Nano Composites ◽  
Pillared Montmorillonite ◽  
Topographic Features ◽  
Transmission Electron

Recently, a new sort of nano-composites has been prepared by incorporating such fine particles as metal oxide microcrystallites and organic polymers into the interlayer space of montmorillonite. Owing to their extremely large specific surface area, the nano-composites are finding wide application[1∼3]. However, the topographic features of the microstructures have not been elucidated as yet In the present work, the microstructures of iron oxide-pillared montmorillonite have been investigated by high-resolution transmission electron microscopy.Iron oxide-pillared montmorillonite was prepared through the procedure essentially the same as that reported by Yamanaka et al. Firstly, 0.125 M aqueous solution of trinuclear acetato-hydroxo iron(III) nitrate, [Fe3(OCOCH3)7 OH.2H2O]NO3, was prepared and then the solution was mixed with an aqueous suspension of 1 wt% clay by continuously stirring at 308 K. The final volume ratio of the latter aqueous solution to the former was 0.4. The clay used was sodium montmorillonite (Kunimine Industrial Co.), having a cation exchange capacity of 100 mequiv/100g. The montmorillonite in the mixed suspension was then centrifuged, followed by washing with deionized water. The washed samples were spread on glass plates, air dried, and then annealed at 673 K for 72 ks in air. The resultant film products were approximately 20 μm in thickness and brown in color.

The microstructure of functionalized poLyacrylonitrile beads for bioseparations

1990 ◽  
Vol 48 (4) ◽  
pp. 1094-1095
Author(s):  
Eduardo A. Kamenetzky ◽  
David A. Ley
Keyword(s):  
Aqueous Solution ◽  
Affinity Chromatography ◽  
Pore Size Distribution ◽  
Pore Size ◽  
Surface Coverage ◽  
Vacuum Impregnation ◽  
Thin Sections ◽  
Selective Staining ◽  
Low Viscosity ◽  
Diamond Knife

The microstructure of polyacrylonitrile (PAN) beads for affinity chromatography bioseparations was studied by TEM of stained ultramicrotomed thin-sections. Microstructural aspects such as overall pore size distribution, the distribution of pores within the beads, and surface coverage of functionalized beads affect performance properties. Stereological methods are used to quantify the internal structure of these chromatographic supports. Details of the process for making the PAN beads are given elsewhere. TEM specimens were obtained by vacuum impregnation with a low-viscosity epoxy and sectioning with a diamond knife. The beads can be observed unstained. However, different surface functionalities can be made evident by selective staining. Amide surface coverage was studied by staining in vapor of a 0.5.% RuO4 aqueous solution for 1 h. RuO4 does not stain PAN but stains, amongst many others, polymers containing an amide moiety.

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