Kinetic analysis of the annealing period in the formation of the poly(A)·2poly(U) triple helix

The slow kinetics of annealing processes in multistranded nucleic acids is spectrophotometrically investigated using poly(A)·2poly(U) as a model system. The absorbance changes at specific wavelengths show that double-helical (A·U) base pairs appear as transient intermediates. The annealing process is identified by the enlargement of triple-helical sequences at the cost of (A·U) base pairs and unpaired (U) residues. A large time range in the reorganization of mismatched chain configurations is characterized by a logarithmic dependence on time. This observation is quantitatively described by a kinetic model developed by Jackson. In Jackson's model the rate-limiting process in the slow annealing phase of maximizing triple-helical sequences, is the removal of strand entanglements, knots, and hairpin loops by complete unwinding of those helical stretches which stabilize the mismatched configurations. The results of the present study are briefly discussed in terms of optimum conditions for hybridization experiments and for the preparation of polynucleotide complexes commonly used to produce interferons.     

Quantitative Bestimmung der wachstumsbedingten Veränderungen in der Ultrastruktur von frei suspendierten Kalluszellen der Petersilie (Petroselinum crispum [Mill.] A. W. Hill)1)

Mittels morphometrischer Methoden wurden die ultrastrukturellen Veränderungen, die in Petersilien-Kalluszellen in Suspensionskultur während des Kulturzyklus ablaufen, quantitativ erfaßt. Stichproben wurden in Abständen von fünf Tagen zu Beginn und zum Ende der logarithmischen Phase und in der stationären Phase der Kultur genommen Embryogenese, Zelldifferenzierungen und Chloroplastenentwicklung finden in den Kulturen nicht statt Nach Beginn der logarithmischen Phase haben die Zellen den höchsten durchschnittlichen Cytoplasmagehalt (55 Volumen-% gegen 40 Volumen-% Vakuolenanteil); das Cytoplasma weist die höchste Ribosomendichte auf, der Nucleolus erreicht seine maximale Ausdehnung Bis zum Ende der logarithmischen Phase erreichen Kern, Plastiden, Mitochondrien und der Golgi-Apparat ihre höchsten Volumenanteile bezogen auf das Cytoplasmavolumen. Die Zellen deponieren Stärke und ätherische Öle In der stationären Phase kommt es zur Vakuolisierung der Zellen (durchschnittlicher Vakuolenanteil 68 Volumen-% gegen 24 Volumen-% Cytoplasmaanteil). Die deponierte Stärke wird bereits zu Beginn der stationären Phase wieder mobilisiert Vom Beginn der logarithmischen Phase bis zum Ende der Kulturzeit kommt es nahezu zu einer Verdoppelung der Wandstärken. Die größte Zunahmerate fällt in die stationäre Phase Wir danken Herrn Prof. Dr. F. MAYER (Göttingen) und Herrn Dr. U. SEITZ (Tübingen) für anregende Diskussionen, Herrn Dr. W. ALFERMANN (Tübingen) für die Gaschromatographie, Fräulein I. HEIMES und Fräulein B. SCHÄFER für technisdie Assistenz. Der Deutschen Forschungsgemeinsdiaft (U.S.) und der Stiftung Volkswagenwerk wird für Sachmittelunterstützung gedankt.     

Bildung und differenzierung der keimblätter bei chrysopa perla (L.)

Zusammenstellung der wesentlichsten Ergebnisse Die Bildung und Segmentierung der Keimblätter beruht auf allgemeiner Zelldifferenzierung des ursprünglich gleichförmigen Blastoderms. Diese Differenzierung geht von einem prothorakalen Differenzierungszentrum aus und schreitet von da nach vorn und hinten weiter. Dadurch entsteht im Längsschnitt des Keimes ein Differenzierungsgefälle, das bis in späte Stadien der Organbildung nachzuweisen ist.Der Unterlagerungsvorgang erfolgt auf der Grundlage der Segmentierung. Er beginnt mit der Einsenkung der Mittelplatte und endet mit der Bildung der Coelomepithelien. Die Einsenkung der Mittelplatte ist auf Zelldifferenzierung zurückzuführen. Die Coelomblätter sind in einer Schichtung der Mesodermzellen vorgebildet, die nach Einsenkung der Mittelplatte unter der Mitte des Ektoderms entsteht.Als spezielle Zelldifferenzierung beginnt die Organbildung im Ektoderm vor, im Mesoderm nach der Unterlagerung. Sie schreitet innerhalb eines jeden Segmentes und in allen Keímschichten von der Mitte des Keimes nach den Seiten fort. Am Chrysopa-Ei konnte these Gesetzmäßigkeit in der Differenzierung des Querschnittes erstmalig bis in alle Einzelheiten der Zelldifferenzierung nachgewiesen werden. Es ist zu erwarten, daß she für die Entwicklung aller Insekten typisch ist.     

On the invariance of visual stimulus efficacy with respect to variable spatial positions

Summary In the fly,Calliphora erythrocephala, visual stimuli presented in an asymmetrical position with respect to the fly elicit roll or tilt movements of the head by which its dorsal part is moved towards the light areas of the surroundings (Figs. 4–7). The influence of passive body roll and tilt (gravitational stimulus) on the amplitude of these active head movements was investigated for two types of visual stimuli: (1) a dark hollow hemisphere presented in different parts of the fly's visual field, and (2) a moving striped pattern stimulating the lateral parts of one eye only.The response characteristics of the flies in the bimodal situation in which the gravitational stimulus was paired with stimulation by the dark hollow hemisphere can be completely described by the addition of the response characteristics for both unimodal situations, i.e. by the gravity-induced and visually induced characteristics (Figs. 8, 9). Therefore, the stimulus efficacy of the dark hollow hemisphere is independent of (=invariant with respect to) the flies' spatial position. The advantage of this type of interaction between gravity and visual stimulation for the control of body posture near the horizontal is discussed.In contrast, the efficacy of moving patterns depends on (=non-invariant with respect to) the spatial position of the walking fly. Regressive pattern movements exhibit their stronger efficacy with respect to progressive ones only when the gravity receptor system of the legs is stimulated. The stronger efficacy of downward vs upward movements can only be demonstrated when the flies are walking horizontally, independently of whether the leg gravity receptor system is stimulated by gravity or not (Fig. 10).The results are discussed with respect (1) to the invariance and non-invariance of the efficacy of visual stimuli with respect to the direction of the field of gravity, (2) to the formation of reference lines by the gravitational field which are used by the walking fly to determine the orientation of visual patterns, and (3) to the possible location of the underlying convergence between gravitationally and visually evoked excitation. As all types of head responses occur only in walking flies, we also discussed the possible influences of some physiological processes like arousal, proprioceptive feedback during walking and various peripheral sensory inputs on the performance of behavioural responses in the fly (Fig. 11).     

The close phylogenetic relationship of Nitrobacter and Rhodopseudomonas palustris

The phylogenetic position of Nitrobacter winogradskyi and two other nitrite-oxidizing bacteria was elucidated comparing oligonucleotides of the 16S ribosomal RNA. Nitrobacter winogradskyi and the Nitrobacter isolate Yukatan are genetically nearly identical; Nitrobacter isolate X14 is more distantly related. Phylogenetically, Nitrobacter is a member of a group of purple non-sulfur bacteria that is defined by various species of Rhodopseudomonas, Rhodomicrobium vannielii, Rhodospirillum rubum and their non-phototrophic relatives. Nitrobacter shares a high sequence similarity to Rhodopseudomonas palustris. These findings are in accord with several common taxonomic characteristics, and in addition support the conversion hypothesis for the origin of this group of chemolithotrophic bacteria.     

Microautoradiographic studies of phloem loading and transport in the leaf of Zea mays L.

Microautoradiographs showed that [¹⁴C]sucrose taken up in the xylem of small and intermediate (longitudinal) vascular bundles of Zea mays leaf strips was quickly accumulated by vascular parenchyma cells abutting the vessels. The first sieve tubes to exhibit ¹⁴C-labeling during the [¹⁴C]sucrose experiments were thick-walled sieve tubes contiguous to the more heavily labeled vascular parenchyma cells. (These two cell types typically have numerous plasmodesmatal connections.) With increasing [¹⁴C]sucrose feeding periods, greater proportions of thick- and thin-walled sieve tubes became labeled, but few of the labeled thin-walled sieve tubes were associated with labeled companion cells. (Only the thin-walled sieve tubes are associated with companion cells.) When portions of leaf strips were exposed to ¹⁴CO₂ for 5 min, the vascular parenchyma cells-regardless of their location in relation to the vessels or sieve tubes-were the most consistently labeled cells of small and intermediate bundles, and label (¹⁴C-photosynthate) appeared in a greater proportion of thin-walled sieve tubes than thick-walled sieve tubes. After a 5-min chase with ¹²CO₂, the thin-walled sieve tubes were more heavily labeled than any other cell type of the leaf. After a 10-min chase with ¹²CO₂, the thin-walled sieve tubes were even more heavily labeled. The companion cells generally were less heavily labeled than their associated thin-walled sieve tubes. Although all of the thick-walled sieve tubes were labeled in portions of leaf strips fed ¹⁴CO₂ for 5 min and given a 10-min ¹²CO₂ chase, only five of 72 vascular bundles below the ¹⁴CO₂-exposed portions contained labeled thick-walled sieve tubes. Moreover, the few labeled thick-walledsieve tubes of the transport region always abutted ¹⁴C-labeled vascular parenchyma cells. The results of this study indicate that (1) the vascular parenchyma cells are able to retrieve at least sucrose from the vessels and transfer it to the thick-walled sieve tubes, (2) the thick-walled sieve tubes are not involved in long-distance transport, and (3) the thin-walled sieve tubes are capable themselves of accumulating sucrose and photosynthates from the apoplast, without the companion cells serving as intermediary cells.     

Structural changes in bacteriorhodopsin induced by electric impulses

Electric impulses of high field intensity (2 × 10⁵ to 3 × 10⁶ Vm^?1, 1 to 20 μs duration) cause transient changes in the optical absorbance of suspended purple membranes of Halobacterium halobium. The electric dichroism at 1 mm NaCL, pH ≈ 6 and at 293K is dependent on field strength, pulse duration and wavelength of the monitoring, plane-polarized light in the range 400 to 650 nm. The optically detected processes are, however, independent of bacteriorhodopsin concentration, of ionic strenght and of the intensity of the monitoring light. These data together with the analysis of time course ands steady state of the reduced dichroism, suggest electric field-sensitive, intramemembraneous structural changes which lead to restricted orientation changes of the chromophore. A thoretical analysis of restricted orientation is developed and applied to the electro-optic data. As a result, it is found that the electric dichroism of purple membrane is associated with a large polarizability anisotropy of 2.4 × 10^?30 Fm² (2.2 × 10^?14 cm³); the electric permanent dipole moment which is involved amounts to 4.7 × 10^?28 Cm(140 Debye). The kinetic data suggest a cyclic reaction scheme with at least five different conformations. The high polarizability is probably due to displaceable ionic groups within the cooperative lattice of bacteriorhodopsin molecules in purple membranes.     

On the occurrence of antimicrobial substances in the course of composting of municipal garbage

Summary Various extracts obtained from different phases of composting municipal garbage were tested for their effect on the growth of Bacillus megaterium and a mixed bacterial population. The results showed that antimicrobial substances are present in the fresh garbage. Their biocidal efficiency decreases during the rotting process and no new antimicrobial substances are produced during rotting. The evolution of heat as well as a certain kind of detoxication is important for the sanitation of garbage by the composting process.Extract from the Dissertation I. in der Schmitten, Giessen 1979     

The influence of prostaglandins on sperm motility

Prostaglandin E₂ and F_2α were measured in ejaculates from 10 fertile and 55 infertile men. Prostaglandin F_2α was negatively correlated with motility (r=0.77; p<0.01) in normal men. In patients with disturbed fertility, prostaglandin F_2α was always higher than in the controls, while prostaglandin E₂ was elevated only in patients with persisting varicocele and in those with very low sperm counts and severely impaired motility. There was neither synthesis of prostaglandins in spermatozoa nor were binding sites for prostaglandin E₂ and F_2α detectable. Inactivation of seminal prostaglandins by incubation with prostaglandin 15-hydroxydehydrogenase resulted in a dramatic fall in motility. The results suggest that prostaglandin F_2α act on motility, but the action is not mediated by receptors.