Low-temperature X-ray microanalysis of the differentiating vascular tissue in root tips of Lemna minor L

The fracture faces of bulk-frozen tissue offer a number of advantages for the analysis of diffusible elements. They are easy to prepare, remain uncontaminated, and, unlike most frozen-hydrated sections, can be shown to exist in a fully hydrated state throughout examination and analysis. Root tips of Lemna minor briefly treated with a polymeric cryoprotectant are quench frozen in melting nitrogen. Fractures are prepared using the AMRAY Biochamber, lightly etched if necessary to reveal surface detail and carbon coated while maintaining the specimen at 110 K. The frozen-hydrated fracture faces are analysed at 110 K using the P/B ratio method which is less sensitive to changes in surface geometry and variations in beam current. The method has been used to investigate the distribution of seven elements (Na+, Mg⁺⁺, P, S, Cl^?, K+ and Ca⁺⁺) in the developing vascular tissue of the root tip. The microprobe can measure relative elemental ratios at the cellular level and the results from this present study reveal important variations in different parts of the root. The younger, more actively dividing cells, appear to have a slightly higher concentration of diffusible ions in comparison to the somewhat older tissues which have begun to differentiate into what are presumed to be functional vascular elements.     

Microstructure-Based Estimation of Strength and Ductility Distributions for $$\alpha +\beta $$ Titanium Alloys

Titanium alloys are processed to develop a wide range of microstructure configurations and therefore material properties. While these properties are typically measured experimentally, a framework for property prediction could greatly enhance alloy design and manufacturing. Here a microstructure-sensitive framework is presented for the prediction of strength and ductility as well as estimates of the bounds in variability for these properties. The framework explicitly considers distributions of microstructure via new approaches for instantiation of structure in synthetic samples. The parametric evaluation strategy, including the finite element simulation package FEpX, is used to create and test virtual polycrystalline samples to evaluate the variability bounds of mechanical properties in Ti-6Al-4V. Critical parameters for the property evaluation framework are provided by measurements of single crystal properties and advanced characterization of microstructure and slip system strengths in 2D and 3D. Property distributions for yield strength and ductility are presented, along with the validation and verification steps undertaken. Comparisons between strain localization and slip activity in virtual samples and in experimental grain-scale strain measurements are also discussed.

     

Low temperature scanning electron microscopy: a review.

Low temperature scanning electron microscopy is useful for morphological and analytical studies both in situations where low temperature techniques are used during specimen preparation and where low temperature stages are used for specimen examination and analysis. Examples are given of different low temperature specimen preparation techniques and how they may be applied to different types of specimen. There are still a number of problems associated with morphological identification in fully frozen-hydrated samples and it is important to carry out parallel studies using more conventional transmission electron microscopy and light microscopy preparation techniques. A number of criteria are presented, some or all of which may be used to establish the existence of the frozen-hydrated state.     

Polymeric cryoprotectants in the preservation of biological ultrastructure. III. Morphological aspects.

Two high molecular weight polymers, polyvinylpyrrolidone (PVP) and hydroxyethyl starch (HES), have been used as cryoprotectants for preparing specimens to be freeze fractured. Solutions of 25% (w/w) suppress the formation of intracellular ice in single cells and tissue blocks from both plants and animals to the extent that fine structural details of the cell can be elucidates. The mode of action of these cryoprotectants, together with the structures they reveal and the peculiar advantages attached to their use, is discussed.     

Very low voltage sputter coating

Very low voltage sputter coating, in the range 175–300 V, has been used to produce finely structured thin films of noble and refractory metals for use in high resolution scanning electron microscopy. There is a marked diminution in the particle size with a decrease in cathode voltage. Although the sputtering times are longer than with conventional diode sputter coating, such times are shorter than those required to produce similar films by Penning or ion-beam sputtering. The refractory metals produce films which are fine grained and suitable for high resolution studies. The method has been used to sputter coat thin layers of aluminium. All attempts at sputtering carbon have failed; the reasons for this are discussed in some detail.     

Editorial

Automated scanning microphotometry provides an objective assessment of the distribution of metal-bearing (MB) amoebocytes in various tissues of the Pacific oyster, Crassostrea gigas. Silver-staining of these cells in paraffin-embedded sections gave good histochemical enhancement for effective photometric discrimination. Metal-associated pixel fractions (MAPF) for 0.41 mm² tissue-fields were calculated from the results of microphotometric scans, giving an estimate of the metal content and an expression of the population density of MB cells. Gut-associated MB cells in oysters obtained from two geographically-separate metalliferous estuaries had similar distribution patterns, with MAPF values that correlated with metal concentrations in visceral mass determined by atomic absorption spectrophotometry (AAS). The metal content of other tissues varied by two orders of magnitude, the gill having the highest MAPF values. Intermediate MAPF values were found for digestive diverticula and the lowest values in the gonad. There was little difference between gut-associated MB cell populations in oysters from the two collection sites, despite differences in size, glycogen content and gonadal maturation. This non-destructive method of tissue microanalysis may provide a better way of assessing tissue metal-load in individual organisms, and one that is independent of physiological variables.