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Dimensions and distribution of intercellular spaces in cryo-planed soybean nodules (1993)

Cauwenberghe, Owen R. ; Newcomb, William ; Canny, Martin J. ; [et al.]

Oxford, UK : Blackwell Publishing Ltd

Physiologia plantarum 89 (1993), S. 0

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ISSN: 1399-3054

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: The ability of legume nodules to regulate their permeability to gas diffusion has been attributed to physiological control over the size and distribution of gas-filed intercellular spaces within the nodule cortex. To examine the size and distribution of intercellular spaces and to determine whether they were filled with gas (high diffusion permeability) or liquid (low diffusion permeability), whole nodules were frozen in liquid nitrogen slush (-210°C), and then either cryo-fractured or cryo-planed before being examined by cold-stage scanning electron microscopy (SEM). The cryo-planed tissue was found to have many advantages over cryo-fractured nodules in providing images which were easier to interpret and quantify. Intercellular spaces throughout the nodule were examined in both tangential and medial planed faces. Since no differences were observed between views in either the size or shape of the open intercellular spaces, it was concluded that the intercellular spaces of nodules were not radially oriented as assumed in many mathematical models of gas diffusion. The inner cortex region in the nodules had the smallest intercellular spaces compared to other zones, and less than 10% of the intercellular spaces were occluded with any type of material in the central zone regions. Vacuum infiltration of nodules with salt solutions and subsequent cryo-planing for SEM examination showed that open and water-filled intercellular spaces could be differentiated. The potential is discussed for using this method to study the mechanism of diffusion barrier regulation in legume nodules.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1399-3054.1993.tb00151.x

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Evidence that short-term regulation of nodule permeability does not occur in the inner cortex (1994)

Cauwenberghe, Owen R. ; Hunt, Stephen ; Newcomb, William ; [et al.]

Oxford, UK : Blackwell Publishing Ltd

Physiologia plantarum 91 (1994), S. 0

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ISSN: 1399-3054

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: Regulation of nodule permeability in response to short-term changes in environmental and physiological conditions is thought to occur by occlusion of intercellular spaces in the nodule inner cortex. To test this hypothesis, the permeability of legume nodules was altered by adapting them to either 20 or 80% O2 over a 2.5-h period. The nodules were then rapidly frozen, cryo-planed and examined under cryo-scanning electron microscopy for differences in the number, area or shape factor of intercellular spaces. Comparisons were made between whole nodules and specific nodule zones (outer cortex, middle cortex, inner cortex and central zone) in each treatment. Gas analysis measurements indicated that nodules equilibrated at 20% O2 had a 6.6-fold higher permeability than those equilibrated at 80% O2 However, no significant differences were observed between pO2 treatments in the number of open intercellular spaces, the cross-sectional area of those spaces, or the proportion of the tissue area present as open space in whole nodules or any nodule zone. Also, although nodules in both treatments possessed a boundary layer of tightly packed cells in the inner cortex, the total area of intercellular spaces between cells bordering this layer did not differ between treatments. Together these observations do not support the currently favored hypothesis that nodule permeability is regulated by opening or occlusion of intercellular spaces in the nodule inner cortex. Highly significant differences (P= 0.0006) were observed between O2 treatments in the shape factor of the open intercellular spaces in all nodule zones. Nodules equilibrated at 80% O2 had significantly more isodiametric spaces while those equilibrated at 20% O2 had more long, narrow spaces. This observation suggests that the critical step in the regulation of nodule permeability to O2 may be localized in the central, infected zone and involve changes in the ratio of the surface area of the intercellular space to the volume of the infected cell.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1399-3054.1994.tb02977.x

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Contributions of the surface of the root tip to the growth of Zea roots in soil (1994)

McCully, Margaret E. ; Canny, Martin J.

Springer

Plant and soil 165 (1994), S. 315-321

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ISSN: 1573-5036

Keywords: cell wal's ; epidermis ; growth ; root development ; soil penetration ; stiffness ; Zea diploperennis ; Zea mays

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract The development of the epidermal layer of roots of Zea is traced from the quiescent centre to the zone where root hairs develop. In the zone of cell division a three layered coat forms on the outside of the epidermal cells consisting of the outer epidermal walls, overlaid by a two-layered pellicle composed of a thick fibrillar inner layer of polysaccharide, and a thin fibrillar outer layer of protein. The epidermal cells divide several times in the same longitudinal file but rarely across a radius to give a new longitudinal file. Thus, the radial walls become much thicker than all but the original transverse walls, and packets of up to 32 daughter cells derived from a single initial may be distinguished. The pellicle develops during these divisions as a continuum over the outer walls of the daughter cells. It is proposed that the pellicle provides a stiffening to the forward end of the root which permits it to penetrate soil without bending. Support for this hypothesis is shown by the Zea mays mutant Ageotropic in which the pellicle is absent, the epidermal surface is disorganized, and which grows crookedly through soil. In the zone of extension growth of normal roots of two Zea species the pellicle thins and disappears. Circumferential strips of the pellicle were peeled off the young epidermal cells and could be stretched to twice their length. This deformation is partly the result of the pellicle stretching and breaking above the attachments of the radial walls. After normal thinning of the pellicle, detachment of the radial walls at their outer ends produces a corrugated surface in the proximal zone of the root tips. In dicotyledons (e.g., soybean), there is no similar pellicle, but a stiff root tip is produced by a long multi-layered root cap, the proximal portion of which covers the elongating epidermal surface.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00008075

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Planing frozen hydrated plant specimens for SEM observation and EDX microanalysis (1994)

Huang, Cheng X. ; Canny, Martin J. ; Oates, Kenneth ; [et al.]

New York, NY [u.a.] : Wiley-Blackwell

Microscopy Research and Technique 28 (1994), S. 67-74

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ISSN: 1059-910X

Keywords: Al coating ; Frozen hydrated specimens ; Gels ; Longitudinal sections ; Microanalysis ; Morphometric analysis ; Plant tissues ; SEM ; Serial sections ; Life and Medical Sciences ; Cell & Developmental Biology

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Natural Sciences in General

Notes: A procedure is described for forming a flat face on a frozen piece of plant tissue, which may then be observed fully-hydrated or lightly etched, and coated or uncoated with a metal film, in scanning electron microscopy (SEM). The frozen sample was planed with a glass knife at -80°C in cryo-ultramicrotome. The sections were discarded, and the planed block face placed on the cold stage in the microscope column, either for observation uncoated at low kV, or for light etching (-90°C) to reveal the cell outlines. If a higher accelerating voltage was needed, the face was given an evaporative coating of Al in the cryo-preparation chamber and returned to the column. The advantages of the planed face over the usual fracture face are illustrated: imaging at a chosen rather than a chance position; clearer cellular and subcellular detail; preservation of hydrated gels like mucilage and swollen cell walls; the possibility of making serial parallel sections through the same piece of tissue; opportunities for accurate morphometric analyses on the planed face; capacity to produce longitudinal sections; preservation of very delicate structures that are destroyed by fixation and drying. A major advantage of the Al-coated planed face is the increased accuracy of energy-dispersive X-ray (EDX) microanalyses on a smooth rather than a rough surface. Tests are included which show that neither the light etching employed, nor successive planing, interferes with the analyses of elements in the frozen face. © 1994 Wiley-Liss, Inc.

Additional Material: 14 Ill.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1002/jemt.1070280108

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