Zur Physiologie und Cytologie der Fettbildung bei Endomyces vernalis

Ohne ZusammenfassungD 93.—Als vorläufige Mitteilung erschien: M. Steiner, Ernährung und Fettbildung bei Endomyces vernalis. Ber. d. Deutsch. bot. Ges. 56, 73, 1938.     

Muscle-specific RING finger-1 interacts with titin to regulate sarcomeric M-line and thick filament structure and may have nuclear functions via its interaction with glucocorticoid modulatory element binding protein-1

Signaling from receptor tyrosine kinases (RTKs)* requires the sequential activation of the small GTPases Ras and Rac. Son of sevenless (Sos-1), a bifunctional guanine nucleotide exchange factor (GEF), activates Ras in vivo and displays Rac-GEF activity in vitro, when engaged in a tricomplex with Eps8 and E3b1-Abi-1, a RTK substrate and an adaptor protein, respectively. A mechanistic understanding of how Sos-1 coordinates Ras and Rac activity is, however, still missing. Here, we demonstrate that (a) Sos-1, E3b1, and Eps8 assemble into a tricomplex in vivo under physiological conditions; (b) Grb2 and E3b1 bind through their SH3 domains to the same binding site on Sos-1, thus determining the formation of either a Sos-1-Grb2 (S/G) or a Sos-1-E3b1-Eps8 (S/E/E8) complex, endowed with Ras- and Rac-specific GEF activities, respectively; (c) the Sos-1-Grb2 complex is disrupted upon RTKs activation, whereas the S/E/E8 complex is not; and (d) in keeping with the previous result, the activation of Ras by growth factors is short-lived, whereas the activation of Rac is sustained. Thus, the involvement of Sos-1 at two distinct and differentially regulated steps of the signaling cascade allows for coordinated activation of Ras and Rac and different duration of their signaling within the cell.     

Comparison and Validation of Methods To Quantify Cry1Ab Toxin from Bacillus thuringiensis for Standardization of Insect Bioassays

Standardization of toxin preparations derived from Bacillus thuringiensis (Berliner) used in laboratory bioassays is critical for accurately assessing possible changes in the susceptibility of field populations of target pests. Different methods were evaluated to quantify Cry1Ab, the toxin expressed by 80% of the commercially available transgenic maize that targets the European corn borer, Ostrinia nubilalis (Hübner). We compared three methods of quantification on three different toxin preparations from independent sources: enzyme-linked immunosorbent assay (ELISA), sodium dodecyl sulfate-polyacrylamide gel electrophoresis and densitometry (SDS-PAGE/densitometry), and the Bradford assay for total protein. The results were compared to those obtained by immunoblot analysis and with the results of toxin bioassays against susceptible laboratory colonies of O. nubilalis. The Bradford method resulted in statistically higher estimates than either ELISA or SDS-PAGE/densitometry but also provided the lowest coefficients of variation (CVs) for estimates of the Cry1Ab concentration (from 2.4 to 5.4%). The CV of estimates obtained by ELISA ranged from 12.8 to 26.5%, whereas the CV of estimates obtained by SDS-PAGE/densitometry ranged from 0.2 to 15.4%. We standardized toxin concentration by using SDS-PAGE/densitometry, which is the only method specific for the 65-kDa Cry1Ab protein and is not confounded by impurities detected by ELISA and Bradford assay for total protein. Bioassays with standardized Cry1Ab preparations based on SDS-PAGE/densitometry showed no significant differences in LC₅₀ values, although there were significant differences in growth inhibition for two of the three Cry1Ab preparations. However, the variation in larval weight caused by toxin source was only 4% of the total variation, and we conclude that standardization of Cry1Ab production and quantification by SDS-PAGE/densitometry may improve data consistency in monitoring efforts to identify changes in insect susceptibility to Cry1Ab.     

Phasenverschiebungen der endogenen Tagesrhythmik durch Reduktion der Atmung

Zusammenfassung der Ergebnisse Untersucht wurden die Phasenverschiebungen durch atmungsreduzierende Einflüsse bei den endogen-tagesperiodischen Primärblattbewegungen vonPhaseolus multiflorus und den Öffnungs- und Schließungsbewegungen vonKalanchoe blossfeldiana.Selbst eine 4stündige Einwirkung einer Temperatur von +2°, die schon Turgorverlust hervorruft, bedingt beiPhaseolus in einigen Phasen des Cyclus nur eine Verzögerung um etwa 2 Std, in anderen Phasen Verzögerungen, die die Dauer der Kälteeinwirkung übersteigen.Eine 4stündige Sauerstoffverdrängung durch Stickstoff bedingt bei beiden Versuchsobjekten nach der Einwirkung in einigen Phasen keine signifikante Verschiebung, nach der Einwirkung in anderen Phasen Verzögerungen, die 4 Std oder etwas mehr erreichen können.Das unterschiedliche Ansprechen der einzelnen Phasen des Cyclus auf Sauerstoffverdrängung durch Stickstoff geht dem unterschiedlichen Ansprechen auf niedrige Temperatur nicht parallel.DNP-Vergiftung wirkt beiPhaseolus ähnlich wie Sauerstoffverdrängung. Jedoch treten hierbei, noch extremer bei KCN-Vergiftung, nicht nur Phasenverzögerungen, sondern auch Vorverlegungen auf.

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The induction of phase shifts in endogenous diurnal rhythms through the reduction of respiration

Summary Experiments were carried out in order to determine the effect of reducing respiration on the phases of endogenous diurnal movements inPhaseolus multiflorus (primary leaves) andKalanchoe blossfeldiana (opening and closing of the flowers). Such an effect was examined by measuring the delay occurring in peak formation, 2 or more days after treatment.In the case ofPhaseolus, treatment for 4 hours at +20°C caused a phase shift of only about 2 hours when given at certain times in the 24 hours cycle. The same treatment at other points in the cycle resulted in a phase shift which greatly exceeded the duration of the treatment (Fig. 1).Periods of anaerobic conditions were provided at different times during the 24 hour cycle. It was found that, in both species, there were points in the 24 hour cycle at which the treatment did not result in phase shifts in the following peaks, and also points at which the treatment resulted in marked phase shifts (Figs. 2, 3 and 4).These points in the 24 hour cycle with no significant response to the anaerobic conditions are not identical with those at which little or no response is obtained after low temperature treatment.Poisons, such as DNP and KCN, can also induce phase shifts. However, both delays and advances in the clock can result from such treatments (Fig. 5). This is interpreted as being due to a more extreme interruption of the energy supply, which not only delays, but also partially upsets the processes involved in the working of the clock.

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Mit 5 Textabbildungen     

Recovery of adenine-nucleotide pools in terrestrial blue-green algae after prolonged drought periods

Summary The response of Nostoc commune and Nostoc flagelliforme (terrestrial blue-green algae), grown in their natural habitat, towards rewetting after prolonged drought periods (2 weeds up to five years) has been investigated. In Nostoc flagelliforme, the energy charge (EC) about 0.18 in dry condition increases rapidly (EC=0.7 after 1 h) and more slowly in a second phase (EC=0.8 after 6 h). The total content of AXP (=ATP+ADP+AMP) apparently increases due to de novo synthesis of adenine nucleotides. ATP-build-up after a drought period is probably provided by oxidative phosphorylation. It has been found to be about the same, regardless of whether the foregoing drought period had been extended over 6 months or 5 years.Dry samples of colony mats of N. commune exhibit very low ATP-, but high ADP-contents. Within 6 h after rewetting, the final level of extractable ATP (60–100 nmol/mg chlorophyll) is recovered.     

Biofilm formation by Salmonella enterica serovar Typhimurium colonizing solid tumours

Systemic administration of Salmonella enterica serovar Typhimurium to tumour bearing mice results in preferential colonization of the tumours and retardation of tumour growth. Although the bacteria are able to invade the tumour cells in vitro, in tumours they were never detected intracellularly. Ultrastructural analysis of Salmonella-colonized tumours revealed that the bacteria had formed biofilms. Interestingly, depletion of neutrophilic granulocytes drastically reduced biofilm formation. Obviously, bacteria form biofilms in response to the immune reactions of the host. Importantly, we tested Salmonella mutants that were no longer able to form biofilms by deleting central regulators of biofilm formation. Such bacteria could be observed intracellularly in immune cells of the host or in tumour cells. Thus, tumour colonizing S. typhimurium might form biofilms as protection against phagocytosis. Since other bacteria are behaving similarly, solid murine tumours might represent a unique model to study biofilm formation in vivo.     

Drosophila projectin: relatedness to titin and twitchin and correlation with lethal(4) 102 CDa and bent-dominant mutants.

We have investigated projectin, a large protein of insect muscles, in Drosophila melanogaster. The 5.3 kilobases of coding sequence reported here contains Class I and Class II motifs characteristic of titin and twitchin, arranged in a three domain ... [II-I-I] [II-I-I] ... pattern. Two mutants mapped to the location of the projectin gene in the 102C subdivision of chromosome 4, lethal(4) 102 CDa and bent-Dominant, have DNA rearrangements within their projectin gene. The lethal(4) 102 CDa mutant has a 141 nucleotide insertion containing stop codons in all three reading frames within an exon sequence, showing that it cannot synthesize normal projectin. Both bent-Dominant and lethal(4) 102 CDa homozygotes die at the completion of embryogenesis because they are unable to escape the egg vitelline membrane. We propose that this hatching failure is due to muscle weakness caused by projectin defects.