Search

We report on the growth and characterization of sapphire single crystals for X-ray optics applications. Structural defects were studied by means of laboratory double-crystal X-ray diffractometry and white-beam synchrotron-radiation topography. The investigations confirmed that the main defect types are dislocations. The best quality crystal was grown using the Kyropoulos technique. Therein the dislocation density was 102-103 cm−2 and a small area with approximately 2*2 mm2 did not show dislocation contrast in many reflections. This crystal has suitable quality for application as a backscattering monochromator. A clear correlation between growth rate and dislocation density is observed, though growth rate is not the only parameter impacting the quality. [ABSTRACT FROM AUTHOR]

The straightforward calculation of small-angle scattering intensity by hard spheres at different concentrations is performed. For the same system of hard spheres, the scattering intensities were found both using the product of the form factor and the structure factor {based on the work of Kinning & Thomas [ Macromolecules, (1984), 17, 1712-1718]} and using the correlation function {based on the work of Kruglov [ J. Appl. Cryst. (2005), 38, 716-720] and Hansen [ J. Appl. Cryst. (2011), 44, 265-271; J. Appl. Cryst. (2012), 45, 381-388]}. All three intensities are in agreement at every concentration. The values of the radii of gyration found from the Guinier plot are shown to be noticeably underestimated compared to the true radius of gyration of a single sphere. Presented are the calculated correction factors that should be applied to the experimentally found radius of gyration of spheres. Also, the concentration effects are shown to have an even greater impact on the radius of gyration of prolate particles that is found from the Guinier plot. [ABSTRACT FROM AUTHOR]

The pattern of changes in the activity of various forms of invertase (acid soluble, alkaline, and acid insoluble) and the content of sugars (glucose, fructose, and sucrose) in the course of plant adaptation to prolonged (6 days) hypothermia (5°C) was investigated in the leaves of potato plants ( Solanum tuberosum L., cv. Desiree) produced in vitro. We used the wild-type plants as a control and transformed plants with carbohydrate metabolism modified by inserting the yeast gene for invertase (apoplastic enzyme). In the course of adaptation to hypothermia, the activity of acid invertase was shown to rise and the content of sucrose and glucose to increase in the leaves of both genotypes. The greatest activity of acid invertases by the third day of cold acclimation corresponded to the peak level of sugars; in transformed plants, these characteristics exceeded those in the control plants. The transformed plants were more cold resistant than the control plants as suggested by the lack of disturbance of ion permeability of their membranes. It was concluded that owing to accumulation of low-molecular carbohydrates in the course of cold acclimation caused by activation of acid invertase cold resistant plants better adapt to temperature drop. [ABSTRACT FROM AUTHOR]

Growth, CO2 exchange, and the ultrastructure of chloroplasts were investigated in the leaves of potato plants ( Solanum tuberosum L., cv. Désirée) of wild type and transformed with a gene for yeast invertase under the control of patatin class I B33 promoter (for apoplastic enzyme) grown in vitro on the Murashige and Skoog medium supplemented with 2% sucrose. At a temperature of 22°C optimal for growth, the transformed plants differed from the plants of wild type in retarded growth and a lower rate of photosynthesis as calculated per plant. On a leaf dry weight basis, photosynthesis of transformed plants was higher than in control plants. Under hypothermia (5°C), dark respiration and especially photosynthesis of transformed plants turned out to be more intense than in control material. After a prolonged exposure to low temperature (6 days at 5°C), in the plants of both genotypes, the ultrastructure of chloroplasts changed. Absolute areas of sections of chloroplasts and starch grains rose, and the area of plastoglobules decreased; in transformed plants, these changes were more pronounced. By some ultrastructural characteristics: a reduction in the cold of relative total area of sections of starch grains and plastoglobules (in percents of the chloroplast section area) and in the number of granal thylakoids (per a chloroplast section area), transformed plants turned out to be more cold resistant than wild-type plants. The obtained results are discussed in connection with changes in source-sink relations in transformed potato plants. These changes modify the balance between photosynthesis and retarded efflux of assimilates, causing an increase in the intracellular level of sugars and a rise in the tolerance to chilling. [ABSTRACT FROM AUTHOR]