On the landing response of the blowfly,Calliphora erythrocephala

The dependence of the landing response on the direction of moving stimuli (periodic gratings, single or double stripes) was studied in blowflies, Calliphora erythrocephala, of both sexes. Directions of motion eliciting maximally strong responses (preference direction) vary with the eye region stimulated: they are distributed radially from a common origin forming a flow-field. This origin lies at the intersection of the eye equators with the median plane of the animal. By changing its body posture relative to the direction of flight, the fly may align the pole of this flow field-with its direction of flight thus maximizing signal flow for the landing approach. Sex-specific differences were found for dorsal eye regions in which the shift of preference directions from vertical to obliquely inclined directions of motion (against the median plane) could only be determined for male flies.     

Nonlinear dynamic transfer characteristics of cells in the peripheral visual pathway of flies

White noise modulated stimuli were employed for studying the transfer characteristics of the intracellularly measured retinula cell responses of the chalky mutant of the blowfly Calliphora erythrocephala Meig. Average depolarization levels varied between 6 and 20 mV. Response modulation depths of up to ±44 % could be achieved. The analysis of the stimulus-response relationship, which takes into account nonlinear properties of the receptor cell response, reveals, that this system is essentially linear for an intermediate frequency range between approximately 5 and 30 Hz. For higher as well as lower frequencies the system becomes increasingly nonlincar.     

Lichtbedingte Orientierungen der Chlorophyllmoleküle in Algenchloroplasten

Der Mesotaenium-Chloroplast hat in Kantenstellung ein Extinktionsmaximum bei λ = 670 nm, in Flächenstellung ein solches bei λ = 680 nm. Chi 660 und 680 sind im Mesotaenium- und im Mougeotia-Chloroplasten parallel zur Thylakoidfläche orientiert. Das gleiche gilt für das Chl 670 des Mougeotia-Chloroplasten, während dieses Chlorophyll im Mesotaenium-Chloroplasten teils flächenparallel und teils flächennormal ausgerichtet ist. Das Molekül bzw. die Porphyrinebene des flächenparallel ausgerichteten Chlorophylls kann mit seinem Rotübergang (Elektronenoscillator für die Absorption roten Lichtes) bzw. mit seinem Blauübergang zusätzlich parallel zur Chloroplastenlängsachse orientiert sein. Die Ausrichtung der Chlorophyllmoleküle steigert sich mit der Lichtintensität, wird jedoch durch DCMU bzw. durch 4-Amino-6-isopropyl-3-thiomethyl-1,2,4-triazin-5-on gehemmt bzw. völlig unterbunden. Herrn Prof. Dr. G. Schulz , Fachbereich Physik der Universität des Saarlandes, danken wir für die Unterstützung bei der Durchführung statistischer Teste, den Farbenfabriken Bayer, Leverkusen, für die Überlassung des 1,2,4-Triazinons.     

Optomotorische Untersuchungen am visuellen System der Stubenfliege Musca domestica L

The compound eye of the housefly Musca domestica L. contains two different types of receptors. The visual acuity of the eye is determined by the divergence angle Δ? between the optical axes of neighbouring ommatidia. Δ? and its dependence on the mean pattern brightness is determined by an evaluation of the optomotor responses elicited from various test patterns. Based on the assumption that the visual fields of both types of receptors approximate the shape of a spatial Gaussian distribution they can be characterized by their half-width, designated as the acceptance angle ΔQ. The contrast transfer from the optical environment onto the receptor cells is limited by ΔQ. It is shown experimentally that ΔQ depends on the mean environmental brightness. The characteristic values Δ? and ΔQ constitute the limiting factors for the light flux received by the receptors. The light flux Φ exciting the receptor cells is proportional to (ΔQ·Δ?)². If the product ΔQ·Δ? is kept constant, there exists a certain ratio \(\frac{{\Delta _\rho }}{{\Delta _\varphi }}\) that leads to an optimal combination of both, contrast transfer and resolution. The ratio \(\frac{{\Delta _\rho }}{{\Delta _\varphi }}\) is experimentally determined and compared with the optimal condition. The torque exerted by fixed flying Muscae has been used as a measure of the reaction strength of the optomotor response elicited by the rotation of cylindrical patterns consisting of periodic distributions of surface brightness. The responses were investigated under different spatial wavelengths, contrasts, contrast frequencies and mean pattern brightness. Detailed results are:

1. The visual acuity (optical resolution power) of the compound eye of Musca is determined by the divergence angle Δ _? between the optical axes of those adjacent ommatidia which are not positioned in the same horizontally oriented row but — closer together — in neighboured rows.
2. Δ? and consequently also the visual acuity do not depend on the mean environmental brightness.
3. The acceptance angle ΔQ changes with the mean brightness of the environment. According to experimental conditions only the minimal acceptance angle Δ _min can be experimentally determined. Δ _min decreases with increasing mean pattern brightness from 3.6°–4.1° to 1.7°.
4. The decrease of ΔQ _min with increasing mean pattern brightness is not caused by a change of the acceptance angles of single receptors. The present tentative explanation is that the centrally located receptors No. 7 and 8 are participating in the uptake of relevant visual information at a critical brightness level.
5. Near the optomotor threshold the large acceptance angle ΔQ _min=3.6° at very dim light would thus be associated with the receptors No. 1 to 6, whereas the smaller acceptance angle ΔQ _min=1.7° with the receptors No. 7 and 8.
6. Due to a sample spacing of Δ?=2°, the acceptance angles of neighbouring receptors No. 1 to 6 show a considerable overlap.
7. Based on anatomical data, the difference in absolute light sensitivity for both receptor systems is calculated. It is predicted that the absorption rate of light quanta in the less sensitive system of the receptors No. 7 and 8 should be reduced by a factor of 24–48 compared to the more sensitive system of the receptors No. 1 to 6. This factor nicely meets the experimentally determined brightness thresholds of both receptor systems.
8. The optimal condition \(\frac{{\Delta _\rho }}{{\Delta _\varphi }}\) is nearly fulfilled by the receptor system No. 7 and 8 of Musca. The experimentally determined ratio amounts to \(\frac{{\Delta _\rho }}{{\Delta _\varphi }}\) =0.83. For the receptor system No. 1 to 6 one finds \(\frac{{\Delta _\rho }}{{\Delta _\varphi }}\) =1.86; in that system the transfer of spatial wavelengths is mainly limited by the reduced contrast transfer which drops to low values before the optical resolution limit is reached.
9. Based on the hypothesis that movement perception of the fly Musca is due to a correlation of sensory data one would expect an optomotor peak reaction at a spatial wavelength of λ _max=8° and a decrease of the optomotor response towards longer spatial wavelengths. The experimental data are in conflict with these predictions. The present notion is that the absence of the expected reaction decrease is not likely to be caused by a saturation effect in the reaction but rather is explainable in terms of a receptor system consisting of larger numbers of receptor types No. 1 to 6 whose excitations being summed before a correlation evaluation takes place.

     

On the influence of fructose-6-phosphate, ammonium, ATP and AMP on the conformation of the phosphofructokinase from rabbit muscle.

By means of circular dichroism measurements in the range from 210-240 nm and 250-300 nm it is shown that conformational changes of the phosphofructokinase from rabbit muscle correlate with the action of effectors on the enzyme. The postulated active and inactive states differ in the secondary structure. Addition of activators causes a conformational change which is interpreted as the transition of the inactive into the active state. At 210-240 nm no reversion could be observed but at 250-300 nm there are some indications for at least partial reversion.     

Characterization of a low molecular weight antigenic protein from the envelope of influenza virus

Eckert, Edward A. (The University of Michigan, Ann Arbor). Characterization of a low molecular weight antigenic protein from the envelope of influenza virus. J. Bacteriol. 92:1430-1434. 1966.-An antigenic protein from the lipid-extracted residue of influenza virus strain PR8 was solubilized with urea-dithiothreitol (DTT). The protein subunits had a sedimentation coefficient of 2S in urea-DTT and reassociated to a 4S state on dialysis. This form of the envelope protein did not agglutinate erythrocytes, but reacted with strain-specific antisera in the complement-fixation and blocking-antigen tests.     

The involvement of lipids in light-induced charge separation in the reaction center of photosystem II

Extraction of PS II particles with 50 mM cholate and 1 M NaCl releases several proteins (33-, 23-, 17- and 13 kDa) and lipids from the thylakoid membrane which are essential for O₂ evolution, dichlorophenolindophenol (DCIP) reduction and for stable charge separation between P680⁺ and Q_A ^-. This work correlates the results on the loss of steady-state rates for O₂ evolution and PS II mediated DCIP photo-reduction with flash absorption changes directly monitoring the reaction center charge separation at 830 nm due to P680⁺, the chlorophyll a donor. Reconstitution of the extracted lipids to the depleted membrane restores the ability to photo-oxidize P680 reversibly and to reduce DCIP, while stimulating O₂ evolution minimally. Addition of the extracted proteins of masses 33-, 23- and 17- kDa produces no further stimulation of DCIP reduction in the presence of an exogenous donor like DPC, but does enhance this rate in the absence of exogenous donors while also stimulating O₂ evolution. The proteins alone in the absence of lipids have little influence on charge separation in the reaction center. Thus lipids are essential for stable charge separation within the reaction center, involving formation of P680⁺ and Q_A ^-.Abbreviations A₈₃₀ Absorption change at 830 nm - Chl Chlorophyll - D₁ primary electron donor to P680 - DCIP 2,6-dichlorophenolindophenol - DPC 1,5-diphenylcarbazide - MOPS 3-(N-morpholino)propanesulfonic acid - P680 reaction center chlorophyll a molecule of photosystem II - PPBQ Phenyl-p-benzoquinone - PS II Photosystem II - Q_A, Q_B first and second quinone acceptors in PS II - V-DCIP rate of DCIP reduction - V-O₂ rate of oxygen evolution - Y water-oxidizing enzyme system - CHAPS 3-Cyclohexylamino-propanesulfonic acid     

Large scale spatial and temporal variation in recruitment to fish populations on coral reefs

Summary Visual census was used to sample young of the year of fish species recruited to each of two habitats on seven lagoonal platform reefs of the Capricorn-Bunker Group, Great Barrier Reef. The reefs sampled span an area 70 km in extent. In 1983, 62 species from 13 families were detected as recruits on reef slope sites. The total number of cruits, and the number of each of 6 of 16 species tested, differed significantly among reefs, despite the fact that differences among sites within reefs did not exist, and that sampled slopes were chosen to be hydrographically, and physiographically as similar as possible. Lagoonal patch reefs were sampled in two years. In 1982, 76 species of 11 families occurred as recruits. In 1983, 86 species of 12 families were recorded. All of 22 species common enough to test showed some significant variation in abundance among reefs, years, or both. For 9 species, significant year x reef interactions occurred, demonstrating that relative recruitment success among reefs varied between years. Reasons for the substantial levels of variability are discussed, and implications for the organisation of reef fish communities are considered.     

Clonal reproduction and patterns of genotypic diversity in Decodon verticillatus (Lythraceae)

Most perennial plants combine sexual reproduction with some form of clonal propagation. These mixed strategies may produce considerable variation among populations in levels of clonal diversity in response to ecological factors limiting one or other reproductive mode. Surveys of style morph frequencies in 163 populations of the eastern North American, clonal, tristylous aquatic, Decodon verticillatus (L.) Ell. (Lythraceae) suggested a wide range of clonal diversity among populations. Populations consisting of a single style morph were most common at the northern margin of the species' range and could have arisen through severe founder events followed by exclusive clonal propagation. Here, we test this hypothesis by comparing allozyme variation in populations monomorphic and polymorphic for style length located in Ontario and Michigan. Each of the four populations monomorphic for style length were fixed for a single three-locus allozyme genotype while the seven trimorphic and five dimorphic populations contained an average of 26 multilocus genotypes each. Measures of genotypic diversity were high in polymorphic populations (average D = 0.93 ± 0.02 standard error; D = 0.00 for all populations monomorphic for style length). Three of the populations monomorphic for style length were fixed for a heterozygous genotype at one of the loci surveyed, suggesting that each consists of a single clone. In contrast, genotype frequencies in polymorphic populations conformed to Hardy-Weinberg proportions indicative of sexual reproduction. The range of clonal diversity found in D. verticillatus is the largest reported for a clonal plant species, although the literature is too limited to determine whether this is truly unusual. Clonal diversity in D. verticillatus is likely to be regulated largely by ecological factors affecting seed production and establishment. However, genetically based sexual sterility also occurs in some populations.