Adaptation of nitrogenase to varying oxygen tension and the role of the vesicle in root nodules of Alnus incana ssp. rugosa

1988 ◽  
Vol 66 (9) ◽  
pp. 1772-1779 ◽  
Author(s):  
Warwick B. Silvester ◽  
Janet K. Silvester ◽  
John G. Torrey
Keyword(s):  
Flow System ◽  
Nitrogenase Activity ◽  
Root Nodules ◽  
Major Change ◽  
Dark Field ◽  
Alnus Incana ◽  
Major Barrier ◽  
Dark Field Microscopy ◽  
Nodule Morphology

Growth of Alnus incana ssp. rugosa plants with root systems at Po2 levels of 5, 21, and 40 kPa showed no significant differences among treatments over a 6-week period. Nitrogenase activity of attached nodulated foot systems run in an opencuvette continuous-flow system generally was responsive to Po2 over a broad range around the optimum. Plants expressed acetylene-induced and oxygen-induced transient declines in nitrogenase activity, from which they spontaneously recovered. Nitrogenase activity was seldom stable at any one Po2 during assay with apparent adaptation to both above- and below-ambient Po2 Nodule morphology showed quantitative decreases in aeration pathways as ambient Po2 was increased, with air spaces in the cortex and infected tissue being significantly affected. The major change in response to Po2 was the change in vesicle structure. Vesicles from nodules at low Po2 showed a vanishingly thin vesicle envelope under dark-field microscopy, while at high Po2 vesicles appeared very bright and apparently thickened. The results suggest that the major barrier to O2 diffusion in Alnus nodules is the vesicle envelope of the bacterium.

Nile red fluorescence demonstrates lipid in the envelope of vesicles from N2-fixing cultures of Frankia

1988 ◽  
Vol 34 (5) ◽  
pp. 656-660 ◽  
Author(s):  
Hayes C. Lamont ◽  
Warwick B. Silvester ◽  
John G. Torrey
Keyword(s):  
Nitrogenase Activity ◽  
Nile Red ◽  
Green Light ◽  
Dark Field ◽  
Free Medium ◽  
Frankia Strain ◽  
Dark Field Microscopy ◽  
Lipid Solvent ◽  
Nile Red Fluorescence ◽  
Fluorescent Stain

Using Nile red as a fluorescent stain for lipid, we investigated the composition of the envelope of vesicles of Frankia strain HFPCcI3 from cultures induced in N-free medium at 1 and 20 kPa O2. Vesicles and nitrogenase activity appeared in the cultures at both pO2; on average, vesicles viewed by dark-field microscopy were larger and had thicker envelopes at 20 kPa O2 than at 1 kPa O2. Envelopes of Nile red-stained vesicles fluoresced red under incident green light. When samples of CcI3 were extracted through a lipid-solvent series and then stained, vesicles still fluoresced red but lacked a distinct peripheral fluorescent ring. These results are consistent with the view that the envelope of Frankia vesicles consists largely of lipid and serves as a barrier to diffusion of O2.

Weak-Beam Imaging of Coherent Twin Boundaries After High-Temperature Deformation

1985 ◽  
Vol 43 ◽  
pp. 242-243
Author(s):  
Krishna Rajan
Keyword(s):  
High Temperature ◽  
Base Alloy ◽  
Dark Field ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Weak Beam ◽  
Dark Field Microscopy ◽  
Cobalt Base Alloy ◽  
Cobalt Base

Weak beam dark field microscopy has been used extensively to study deformation induced intragranular defects in materials. However as noted by Tones et al weak beam imaging is also an asset in examining intergranular defects. The localisation of strain contrast close to the defect core by weak beam imaging allows the interaction of matrix dislocations with the boundary (to form extrinsic dislocations) to be studied more easily. Also, the reduction in extinction distance with weak beam microscopy produces a higher density of extinction contours, which allows topographical discontinuities associated with long range strain fields to be more readily observed.Thus in the present study, where we were interested in interfacial phenomena during high temperature deformation processing of a cobalt base alloy (Co-Cr-Mo), weak beam imaging was used to obtain a better understanding of the role of intergranular defects.

Nitrogenase activity in response to restricted shoot growth in Alnus incana

1983 ◽  
Vol 61 (11) ◽  
pp. 2949-2955 ◽  
Author(s):  
Kerstin Huss-Danell ◽  
Anita Sellstedt
Keyword(s):  
Root Biomass ◽  
Shoot Growth ◽  
Nitrogenase Activity ◽  
Root Nodules ◽  
Alnus Incana ◽  
Nitrogen Fixing ◽  
Combined Nitrogen ◽  
Carbon Compounds ◽  
Source Sink ◽  
Nitrogen Percentage

In the Alnus–Frankia symbiosis the nitrogen-fixing root nodules are one of the sinks for carbon compounds newly formed in photosynthesis and exported from the leaves (source). The competition for assimilates between shoot tips and root nodules was studied by reducing shoot growth. Cloned plants of Alnus incana (L.) Moench were grown without combined nitrogen in a growth chamber. Shoot growth was inhibited by excision of all buds or by induced dormancy. The experiments showed an increased root biomass in the treated plants, indicating a changed source–sink balance. The treatments never caused an increased nitrogenase activity (C2H2-dependent C2H4 production); rather it was decreased. The nitrogenase activity was always correlated with leaf areas. It was also correlated with growth, which is shown by the similar nitrogen percentage in intact and treated plants.

The role of oxygen diffusion from the shoots and nodule roots in nitrogen fixation by root nodules of Myrica gale

1978 ◽  
Vol 56 (11) ◽  
pp. 1365-1371 ◽  
Author(s):  
John Tjepkema
Keyword(s):  
Nitrogen Fixation ◽  
Oxygen Uptake ◽  
Aqueous Phase ◽  
Acetylene Reduction ◽  
Nitrogenase Activity ◽  
Root Nodules ◽  
Myrica Gale ◽  
Before And After ◽  
Whole Plants

Nitrogenase activity (acetylene reduction) and oxygen uptake by root nodules of Myrica gale L. were measured before and after removal of nodule roots. There was no significant effect of nodule root removal when respiration was measured in the gas phase (0.05–0.2 atm pO2 (1 atm = 101.325 kPa)) or acetylene reduction in a stirred aqueous phase at 0.2 atm pO2. However, when acetylene reduction was measured in 0.05 atm pO2 in an unstirred aqueous phase, there was a 66 to 76% reduction in activity. These results indicate that nodule roots are important for oxygen uptake when the nodules are present in an aqueous phase at low pO2, which is probably the normal environmental conditions for many of the nodules. Other measurements showed that diffusion of oxygen from the shoot to the root nodules is not important for nitrogen fixation. These measurements were done on whole plants with the shoots in air (0.20 atm pO2) and the roots in water at the desired pO2 value. With 0.0 atmpO2 in the root environment, the rate of acetylene reduction was only 4% of the rate at 0.2 atmpO2. Thus, only small amounts of oxygen are transported from the shoot to the nodules.

Elastic Scattering in Electron Microscopy

1973 ◽  
Vol 31 ◽  
pp. 252-253
Author(s):  
J. Langmore ◽  
M. Isaacson ◽  
J. Wall ◽  
A. V. Crewe
Keyword(s):  
Electron Microscopy ◽  
Elastic Scattering ◽  
Cross Section ◽  
Quantum Noise ◽  
Dark Field ◽  
Elastic Cross Section ◽  
Biological Molecules ◽  
Dark Field Microscopy ◽  
Field Systems ◽  
Effects Of Radiation

High resolution dark field microscopy is becoming an important tool for the investigation of unstained and specifically stained biological molecules. Of primary consideration to the microscopist is the interpretation of image Intensities and the effects of radiation damage to the specimen. Ignoring inelastic scattering, the image intensity is directly related to the collected elastic scattering cross section, σɳ, which is the product of the total elastic cross section, σ and the eficiency of the microscope system at imaging these electrons, η. The number of potentially bond damaging events resulting from the beam exposure required to reduce the effect of quantum noise in the image to a given level is proportional to 1/η. We wish to compare η in three dark field systems.

Simulated Dark-Field Electron Micrographs of Point Defects and Organometallics

1975 ◽  
Vol 33 ◽  
pp. 200-201
Author(s):  
William Krakow
Keyword(s):  
Electron Micrographs ◽  
Point Defects ◽  
Structure Determination ◽  
Atomic Structure ◽  
Image Interpretation ◽  
Dark Field ◽  
Field Electron ◽  
Dark Field Microscopy ◽  
Dark Field Electron

Tilted beam dark-field microscopy has been applied to atomic structure determination in perfect crystals, several synthesized molecules with heavy atcm markers and in the study of displaced atoms in crystals. Interpretation of this information in terms of atom positions and atom correlations is not straightforward. Therefore, calculated dark-field images can be an invaluable aid in image interpretation.

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