Aerosol activity measurements associated with the burning of peat materials (evacuation zone of the Bryansk Region).

In April and August 2015, a massive fire occurred in the Chernobyl Exclusion zone. The fire spread to neighboring areas due to the prevailing strong winds. In this paper, we analyze the peat fires as a unique source of radioactive contamination. After an expedition directly to the peat fire site (the evacuation zone of the Bryansk region), we collected a number of aerosol samples. We came to the conclusion that peat fires cannot be the reason for radioactive particle transport in the Bryansk region as well as in the Chernobyl evacuation zone. During the peat fire, radioactive contamination was not transferred by aerosols beyond 500 m. The 137Cs concentration in the aerosol filters varied between 0.55 and 0.64 Bq/m3, and that at the same distance from the fire seat and peat edge was 4.4∙10-3 Bq/m3; the activity values in the peat bog and in the nearest inhabited locality did not exceed the background values. Strontium-90 was not found in aerosol samples. The soil-to-air transport rate of 137Cs was 2.7∙10-6. After the Chernobyl accident, the majority of the 137Cs was incorporated into the structure of clay minerals, and these did not change during the peat fire. The mobility of 137Cs in the flight peat material particles was established. To confirm the territory status of the evacuation zone, we also collected some food samples. Berries and mushrooms consumed at the assumed rate for dose estimation would result in doses that exceed the public dose limit by approximately a factor of five.

Changes in vacuolation in the root apex cells of soybean seedlings in microgravity.

Changes in the vacuolation in root apex cells of soybean (Glycine max L. [Merr.]) seedlings grown in microgravity were investigated. Spaceflight and ground control seedlings were grown in the absence or presence of KMnO4 (to remove ethylene) for 6 days. After landing, in order to study of cell ultrastructure and subcellular free calcium ion distribution, seedling root apices were fixed in 2.5% (w/v) glutaraldehyde in 0.1 M cacodylate buffer and 2% (w/v) glutaraldehyde, 2.5% (w/v) formaldehyde, 2% (w/v) potassium antimonate K[Sb(OH)6] in 0.1 M K2HPO4 buffer with an osmolarity (calculated theoretically) of 0.45 and 1.26 osmol. The concentrations of ethylene in all spaceflight canisters were significantly higher than in the ground control canisters. Seedling growth was reduced in the spaceflight-exposed plants. Additionally, the spaceflight-exposed plants exhibited progressive vacuolation in the root apex cells, particularly in the columella cells, to a greater degree than the ground controls. Plasmolysis was observed in columella cells of spaceflight roots fixed in solutions with relatively high osmolarity (1.26 osmol). The appearance of plasmolysis permitted the evaluation of the water status of cells. The water potential of the spaceflight cells was higher than the surrounding fixative solution. A decrease in osmotic potential and/or an increase in turgor potential may have induced increases in cell water potential. However, the plasmolysed (i.e. non-turgid) cells implied that increases in water potential were accompanied with a decrease in osmotic potential. In such cells changes in vacuolation may have been involved to maintain turgor pressure or may have been a result of intensification of other vacuolar functions like digestion and storage.

Cytochemical localization of calcium in soybean root cap cells in microgravity.

The antimonate precipitation technique was used to evaluate the effects of microgravity and ethylene on the cellular and subcellular distribution of free calcium ions in soybean root apices. Soybean (Glycine max L. [Merr.]) dry seeds were launched, activated by hydration, and germinated in the presence of KMnO4 (to remove ethylene) and in its absence onboard the space shuttle Columbia during the STS-87 mission. Primary root apices of 6-day old seedlings were fixed for electron microscopy after landing. Ultrastructural studies indicated that antimonate precipitation appeared as individual electron-dense particles which were more or less round in shape and varied in diameter from 10 nm (minimum size beginning from which the particles were well identified) to 90 nm. It was revealed that analyzed root cap cells varied in both the precipitate particle sizes and the amount particles per unit of the cellular area. In both flight and ground control treatments, antimonate precipitation level increases from apical meristem cells to peripheral (secretory) cells of root apices. In root cap statocytes, subcellular localization of precipitate particles was revealed in the cytoplasm, nucleus and small vacuoles. The quantitative analysis showed a reduction of precipitate density in the cytoplasm and the nucleus, and an increase in precipitate density in the vacuoles from statocytes of both spaceflight treatments in comparison with ground controls.

Crystallization and structure determination of the catalytic trimer of Methanococcus jannaschii aspartate transcarbamoylase.

Aspartate transcarbamoylase (ATCase) catalyzes the first step in the pyrimidine biosynthetic pathway, the reaction between carbamoyl phosphate and L-aspartate to form N-carbamoyl-L-aspartate and phosphate. The structural analysis of the ATCase catalytic trimer from Methanococcus jannaschii, a unicellular thermophilic archaeabacterium, has been undertaken in order to gain insight into the structural features that are responsible for the thermostability of the enzyme. As a first step, the catalytic trimer was crystallized in space group R32, with unit-cell parameters a = b = 265.3, c = 195.5 A and two trimers in the asymmetric unit. Its structure was determined using molecular replacement and Patterson methods. In general, structures containing multiple copies of molecules in the asymmetric unit are difficult to determine. In this case, the two trimers in the asymmetric unit are parallel to each other and use of the Patterson function greatly simplified the structure solution.

Characterization of the aspartate transcarbamoylase from Methanococcus jannaschii.

The genes from the thermophilic archaeabacterium Methanococcus jannaschii that code for the putative catalytic and regulatory chains of aspartate transcarbamoylase were expressed at high levels in Escherichia coli. Only the M. jannaschii PyrB (Mj-PyrB) gene product exhibited catalytic activity. A purification protocol was devised for the Mj-PyrB and M. jannaschii PyrI (Mj-PyrI) gene products. Molecular weight measurements of the Mj-PyrB and Mj-PyrI gene products revealed that the Mj-PyrB gene product is a trimer and the Mj-PyrI gene product is a dimer. Preliminary characterization of the aspartate transcarbamoylase from M. jannaschii cell-free extract revealed that the enzyme has a similar molecular weight to that of the E. coli holoenzyme. Kinetic analysis of the M. jannaschii aspartate transcarbamoylase from the cell-free extract indicates that the enzyme exhibited limited homotropic cooperativity and little if any regulatory properties. The purified Mj-catalytic trimer exhibited hyperbolic kinetics, with an activation energy similar to that observed for the E. coli catalytic trimer. Homology models of the Mj-PyrB and Mj-PyrI gene products were constructed based on the three-dimensional structures of the homologous E. coli proteins. The residues known to be critical for catalysis, regulation, and formation of the quaternary structure from the well characterized E. coli aspartate transcarbamoylase were compared.

Microgravity mediated changes in phytoferritin accumulation in soybean root cap cells.

Phytoferritin is an iron-protein complex analogous to the ferritin found in mammalian, bacteria and fungi cells. Phytoferritin molecules are large proteins, about 10.5 nm in diameter, visualised in an electron microscope as discrete, electron dense particles with iron-containing core, where several thousand atoms of iron lie within the proteinaceous shell (apoferritin). In higher plants, a plastid stroma is the site of phytoferritin storage. Phytoferritin is seen in all types of plastids. It is considered to be a mechanism used by cells to store iron in a non-toxic form. Phytoferritin-bound iron may subsequently be used to form iron-containing components. It was shown that low levels of phytoferritin are synthesised in normal green leaves, whereas chlorotic leaves do not have a measurable amount of phytoferritin and leaves of iron-loaded seedlings contain a high level of total iron, and phytoferritin well-filled by iron. Phytoferritin accumulation was observed in photosynthetic inactivity chloroplasts during senescence and disease. In this study we analised the effects of microgravity and ethylene on production of phytoferritin in the root cap columella cells of soybean seedlings.