Statistical study of rapid mechanodependent cell movements in deformed explants of African clawed frog Xenopus laevis embryonic tissues

Computer analysis of artificially deformed (stretched or compressed) double explants (sandwiches) of the blastocoel roof (BRs) and suprablastoporal region (SBRs) of African clawed frog Xenopus laevis early gastrula has been performed using frames of time-lapse microfilming. During the first 14 min after cutting off, the velocities and displacement angles of several hundreds of cells relative to one another, as well as to fixed points and the extension axis, were measured in the control and deformed samples. It has been found that the deformation of samples leads to a rapid reorientation of large cell masses and increase in the velocities of movements along the extension axes or perpendicularly to the compression axes. In addition, an increase in the velocities of mutual cell displacements in the stretched BRs and cell convergence to the extension axes have been observed. Comparison of different angular sectors demonstrates a statistically significant positive correlation between the mean velocities of cell movements and the number of cells moving within an individual sector. This suggests cooperativity of mechanodependent cell movements. In general, these results demonstrate an important role of mechanical factors in regulation of collective cell movements.     

Salicylic acid induces resistance to <Emphasis Type="Italic">Septoria nodorum</Emphasis> berk. in wheat

The effect of salicylic acid (SA) on oxalate oxidase and peroxidase activities and hydrogen peroxide (H₂O₂) production in leaf cells has been studied in wheat of the susceptible cultivar Zhnitsa infected by Septoria nodorum, a pathogen of wheat leaf blotch. The results show that fungal hyphae spread into interstices between mesophyll cells and that infected tissues contain H₂O₂. Treatment with SA results in enhanced H₂O₂ production in mesophyll cells, which is due to activation of oxalate oxidase and peroxidase in the cell wall. It is proposed that the modulating effect of SA on oxidoreductase activities is involved in the induction of protective response to fungal infection in wheat plants.     

Effect of hydrogen peroxide on morphological characteristics and resistance of wheat calluses to <Emphasis Type="Italic">T. caries</Emphasis> Tul.

We studied the effect of hydrogen peroxide on morphological characteristics and resistance of common wheat calluses ( Triticum aestivum L.) to Tilletia caries Tul. The induction of the defense response and morphogenesis in calluses depended on H₂O₂ concentration. A correlation was revealed between the elevated concentration of hydrogen peroxide in wheat calluses and high activity of oxalate oxidase in the cell wall. Administration of H₂O₂ into the callus culture medium was followed by rhizogenesis, induced the formation of dense regions, and inhibited fungal growth on calluses. Hydrogen peroxide at high concentrations was less potent in inhibiting the growth of fungi. A relationship was found between oxalate oxidase activity, H₂O₂ concentration, and morphogenetic and defense responses of calluses induced by exogenous hydrogen peroxide. These data suggest that the induction of H₂O₂ generation is one of the approaches to increase callus resistance.     

Cloning, Characterization, and Functional Expression in Escherichia coli of argH Encoding Argininosuccinate Lyase in the Cyanobacterium Nostoc sp. Strain PCC 73102

A gene argH, encoding argininosuccinate lyase (ASL), has been cloned from a cosmid library of the filamentous cyanobacterium Nostoc sp. strain PCC 73102. The argH open reading frame encodes a protein comprised of 461 amino acids with a calculated molecular mass of 51,349 Da. Protein sequence comparisons reveal significant similarities of the Nostoc PCC 73102 ASL to related proteins from other organisms. In an Escherichia coliΔargH strain, the Nostoc PCC 73102 ASL expressed from a recombinant plasmid could restore the ability to grow on medium without arginine. Moreover, cell extracts show a specific ASL activity of 16.2 nmoles of urea · min⁻¹· (mg protein)⁻¹. Partially purified, His-tagged ASL runs as a 53-kDa protein band in SDS-PAGE and about 215-kDa protein in native-PAGE, suggesting that the native protein is a tetramer. Received: 6 December 2000 / Accepted: 9 February 2001     

Sorption of neutral red by actomyosin threads during contraction and heating]

Studies of the equilibrium distribution of the cation dye-neutral red by actomyosin threads allowed to establish the fact that different concentrations of dye reveal the existence of different bonds with contractile proteins. Firm bonds (7.3 ccal/M) are discovered at low dye concentrations, and weaker bonds (4.5 ccal/M) are seen at higher concentrations. The contraction of actomyosin threads evoked by ATP or heating is accompanied with similar changes, i. e. by the diminishing of the maximum dye sorption within the range of low dye concentrations and by the increase in the maximum dye sorption within the range of high concentrations.     

Characteristics of the motor potentials in disorders of the subcortical motor structures of the human brain

Properties of motor potentials (MPs) were studied in patients with disturbance of function of subcortical motor structures--disturbance causing parkinsonism manifestations. MPs components are singled out preceding movement--"readiness potential" (N1), "motor potential" (N2) and MP components which are electrophysiological correlates of realization processes (component P2) and movement completion (component N3). It is revealed that MPs in patients with parkinsonism are changed in comparison with the norm; the most significant differences are observed in components N1, P2, N3, what is expressed in prolongation and a certain amplitude decrease of these components. Amplitude-temporal parameters most similar to the norm belong to the component N2, which is considered as an electrophysiological correlate of movement triggering. A hypothesis is suggested on its cortical origin.     

Introduction of two chromosomal translocations of Sus scrofa nigripes and Sus scrofa scrofa into the genome of Sus scrofa domestica

Summary Hybrids between wild and domestic pigs with two types of translocations in the karyotype were studied. The translocations of type I were first detected in a population of the Middle Asian wild boars. Type II was identified in a populations of the Central European subspecies. A large number of Middle Asian and Central European hybrids and their F₁-F₃ hybrids from crosses with domestic pigs were viable. By means of differential chromosome staining, the mechanism of the formation of synthetic karyotypes, as well as some features of translocation inheritance, were established.The introduction of two translocations into a single genome and the same chromosome set of these hybrids not only modified chromosome number, but also the composition of the linkage groups. The hybrids heterozygous for two translocations and their hybrid progeny are characterized by an obligatory heterozygozity for a large number of genes, gene complexes and linked genes. It is suggested that this heterozygozity may be associated with heterotic events. The use of such hybrids in pig breeding may provide heterosis for viability and productivity.     

Plant resistance inductors and active forms of oxygen. II. The influence of chitooligosaccharides on the production of hydrogen peroxide with the involvement of oxalate oxidase in common cultures of wheat calluses and bunt pathogen

We have studied the influence of various concentrations of chitooligosaccharides (CO) on hydrogen peroxide (H2O2) generation, with the involvement of oxalate oxidase (OO), in rhizoids and in zones of hard brand pathogen penetration, as well as on oxalate oxidase activity in wheat calluses. In the control group, diaminobenzidin (DAB)-staining was typical of 30% of peripheral rhizoid cells, which provided their resistance during infection. In the zone of fungus penetration, the appearance of DAB-stained parenchyma-like cells was observed. Simultaneously, the activity OO cytoplasmic fraction increased, whereas OO activity in its ion-bound fraction was suppressed. Low concentrations of medication induced rhizoid formation, increased the number of DAB-stained cells in the pathogen penetration zone, and induced OO activity in cytoplasmic and ionically cell wall-bound fractions. On the contrary, a high concentration of CO (100 mg/ml) suppressed rhizoid formation, Oo activity and the fungus growth. The discovered correlation between enzymatic activation under CO influence, the high level of protective response during infection, and the intensity of rhizoid formation may suggest the community of protective and morphogenetic mechanisms of reactions in plant cells in respect to hydrogen peroxide production.     

Hydrogenases in Nostoc sp. Strain PCC 73102, a Strain Lacking a Bidirectional Enzyme

The present study was carried out in order to examine and characterize the bidirectional hydrogenase in the cyanobacterium Nostoc sp. strain PCC 73102. Southern hybridizations with the probes Av1 and Av3 (hoxY and hoxH, bidirectional hydrogenase small and large subunits, respectively) revealed the occurrence of corresponding sequences in Anabaena variabilis (control), Anabaena sp. strain PCC 7120, and Nostoc muscorum but not in Nostoc sp. strain PCC 73102. As a control, hybridizations with the probe hup2 (hupL, uptake hydrogenase large subunit) demonstrated the presence of a corresponding gene in all the cyanobacteria tested, including Nostoc sp. strain PCC 73102. Moreover, with three different growth media, a bidirectional enzyme that was functional in vivo was observed in N. muscorum, Anabaena sp. strain PCC 7120, and A. variabilis, whereas Nostoc sp. strain PCC 73102 consistently lacked any detectable in vivo activity. Similar results were obtained when assaying for the presence of an enzyme that is functional in vitro. Native polyacrylamide gel electrophoresis followed by in situ hydrogenase activity staining was used to demonstrate the presence or absence of a functional enzyme. Again, bands corresponding to hydrogenase activity were observed for N. muscorum, Anabaena sp. strain PCC 7120, and A. variabilis but not for Nostoc sp. strain PCC 73102. In conclusion, we were unable to detect a bidirectional hydrogenase in Nostoc sp. strain PCC 73102 with specific physiological and molecular techniques. The same techniques clearly showed the presence of an inducible bidirectional enzyme and corresponding structural genes in N. muscorum, Anabaena sp. strain PCC 7120, and A. variabilis. Hence, Nostoc sp. strain PCC 73102 seems to be an unusual cyanobacterium and an interesting candidate for future biotechnological applications.