Abundanzdynamik und reproduktionsphasen limnophiler tricladen (Turbellaria) Aus stehenden kleingewässern

Dynamics of abundance and reproductive cycles of limnophileous triclads (Turbellaria) from little ponds.

1. Studying 18 little ponds in Lower Southern-Saxonia (West-Germany), in 14 ponds seven triclad-species were found.
2. Phagocata vitta occurs from October to July in 1–2 generations. In the area the species reproduces by fissipary. Maximum abundances and rates of reproduction are reached in December and January. In the ponds, where P. vitta and Dugesia polychroa live together, there is no competition between the two species.
3. After dry periods Dendrocoelum hercynicum emigrates from interstitial habitats as facultative inhabitant of surface-waters.
4. In low abundances Dendrocoelum lacteum lives in one pond only. The breeding period (production of cocoons) lasts from January to March. Low densities of this species are probable caused by interspecific food-competition with Polycelis nigra.
5. Likewise, Dugesia tigrina inhabits only one pond. The species is competitive to P. nigra at temperatures of about 20°C. High abundances in the months July to October fall together with high fissipareous-rates.
6. Dugesia polychroa occurs in low densities over the year or dependent on dry-periods. Cocoons are produced between March and May, in low numbers till autumn.
7. In the stagnant pond Bursfelde Polycelis nigra is the absolute dominant triclad-species with densities of up to 800 individuals/0,I m³. The maximum-abundances are caused by two intense reproductive periods in spring and autumn, together with optimum temperatures and food conditions.

     

Synthesis and hydrolysis of ATP by intact chloroplasts under flash illumination and in darkness

ATP concentrations were measured in isolated intact spinach chloroplasts under various light and dark conditions. The following results were obtained: (1) Even in darkened chloroplasts and in the absence of exogenous substrates, ATP levels in the chloroplast stroma were significant. They decreased on addition of glycerate, phosphoglycerate or dihydroxyacetone phosphate. When dihydroxyacetone phosphate and oxaloacetate were added together, ATP levels increased in darkened chloroplasts owing to substrate level phosphorylation. (2) Under illumination with saturating single turnover flashes, oxygen evolution in the presence of phosphoglycerate, whose reduction requires ATP, was no lower on a unit flash basis at the low flash frequency of 2 Hz than at higher frequencies. Quenching of 9-aminoacridine fluorescence, which indicates the formation of a proton gradient in intact chloroplasts, decreased with decreasing flash frequencies, until there was no significant fluorescence quenching at a flash frequency of about 2 Hz. In contrast to intact chloroplasts, broken chloroplasts did not phosphorylate much ADP at the low flash frequency of 2 Hz. (3) Flashing at extremely low frequencies (0.2 Hz) caused ATP hydrolysis rather than ATP synthesis in intact chloroplasts. At higher flash frequencies, synthesis replaced hydrolysis. Still, even at high frequencies (10 Hz), the first flashes of a series of flashes given after a long dark time always decreased chloroplast ATP levels.From these results, it is concluded that the enzyme, which mediates ATP synthesis in the light, is inactive in darkened intact chloroplasts. Its light activation can be separated from the formation of the high energy condition, which results in ATP synthesis. After its activation, the enzyme catalyzes a reversible reaction.     

Loss of function of biomembranes and solubilization of membrane proteins during freezing

Isolated thylakoid membranes are damaged during freezing in dilute salt solutions, as shown by the inactivation of photochemical thylakoid reactions. After freezing, a number of membrane proteins were found in the particle-free supernatant. Up to 5% of the total membrane protein was solubilized by freezing, and the pattern of released proteins as seen in sodium dodecyl sulfate gel electrophoretograms was influenced by the nature of the solutes present. Membranes protected by sucrose did not release much protein during freezing. Concentrated salt solutions caused protein release also in the absence of freezing. Among the proteins released were ferredoxin—NADP⁺ reductase, plastocyanin and coupling factor CF₁. Subunits of CF₁ were found in different proportions in the supernatants of thylakoid suspensions after freezing in the presence of different salts. Cyclic photophosphorylation was largely inactivated before significant protein release could be detected.It is suggested that protein release is the final consequence of the non-specific suppression of intramembrane ionic interactions by the high ionic strength created in the vicinity of the membranes by the accumulation of salts during slow freezing. Salt effects on water structure and alterations of nonpolar membrane interactions by the incorporation of (protonated) lipophilic anions from organic salts into the membrane phase during freezing may also be involved.     

Dynamic light-scattering studies of internal motions in DNA. I. Applicability of the rouse-zimm model

The intermediate scattering function G(K,t) for any polymer model obeying a linear separable Langevin equation can be expressed in terms of the eigenvalues and eigenvectors of its normal coordinate transformation. An algorithm for the extract numerical evaluation of G(K,t) for linear Rouse-Zimm chains in the presence of hydrodynamic interaction has been developed. The computed G(K,t)² were fit to C(t) = A exp(?t/τA) + B, and apparent diffusion coefficients calculated according to D_app ≡ 1/(2τ_AK²). G(K,t)² was surprisingly well-fit by single-exponential decays, especially at both small and large values of Kb, where K is the scattering vector and b the root-mean-squared subunit extension. Plots of D_app vs K² in-variably showed a sigmoidal rise from D₀ at K² = O up to a constant plateau value at large K²b². Analytical expression for G(K,t), exact in the limit of short times, were obtained for circular Rouse-Zimm chains with and without hydrodynamic interaction, and also for free-draining linear chains, and in addition for the independent-segment-mean-force (ISMF) model. The predicted behaviors for G(K,t) at large Kb (or KR_G) was found in all cases to be single-exponential with 1/τ ∝ K² at large Kb, in agreement with the computational results. A simple procedure for estamating all parameter of the Rouse-Zimm model from a plot of D_app vs K² is proposed. Experimental data for both native and pH-denatured calf-thymus DNA in 1.0M Nacl with and without EDTA clearly plateau behavior of D_app at large values of K, in harmony with the present Rouse-Zimm and ISMF theories, and in sharp contrast to previous predictions based on the Rouse-Zimm model.     

Brownian motion of highly charged poly(L-lysine). Effects of salt and polyion concentration

The Brownian motion of a single sample of high-molecular-weight poly(L -lysine) [(Lys)_n, n = 955] has been studied by dynamic light scattering over a wide range of NaBr concentrations and at three different polyion concentrations. A substantial decrease in scattered intensity is associated with the transition from the ordinary phase to the low-salt extraordinary phase. At the salt concentration where the transition takes place the relaxations are non-exponential and appear to exhibit at all angles a rapid relaxation (τ ? 10 μsec) that is presumed to be a manifestation of the kinetics of the transition process. The K² dependence of the slow relaxation rates in the extraordinary phase has been confirmed within the experimental error. The extrapolated infinite-dilution values of the diffusion coefficients in the ordinary phase are observed to decline precipitously below 10^?2M salt to astonishingly small values, indicating a dramatic rise in the friction factors of the isolated polyions. An extensive discussion of these findings in relation to the theory employed here and to existing data in the literature is also given.     

The protective action of disodium cromoglycate on alveolar macrophages in phagocytosis of fibrogenic silica.

Treatment of fibrogenic silica (DQ-12) with Disodium Cromoglycate (DSCG) prior to its in-vitro and in-vivo phagocytosis by alveolar macrophages prevents the destruction of the cells and the fibrosis of lung tissue which are a consequence of phagocytosis. However, the treatment of alveolar macrophages with DSCG before phagocytosis of the silica had no, or a negligible, protective effect on the cells. Acid phosphatase activity which was significantly enhanced above the control in cells phagocytosing the silica was returned to the range found in phagocytosis of inert dust when silica treated with DSCG was phagocytized. The inhibitor of DNA- dependent RNA synthesis actinomycin D caused an increase of acid phosphatase activity. DSCG did not depress the phagocytic ability of alveolar macrophages. It appears that the catabolic enzyme process predominant in cells phagocytosing DQ-12 was under control in cells phagocytosing DQ-12 treated with DSCG and that DSCG probably acted as a regulator of the factors permitting catabolism. From the results it is suggested that the equilibrium of the enzyme reactions which accompany phagocytosis was such that the integrity of the phagocytes was preserved.     

Distribution of RNA polymerase on Drosophila polytene chromosomes as studied by indirect immunofluorescence

Using indirect immunofluorescence visualization techniques we investigated the in situ distribution of RNA polymerase B on Drosophila melanogaster polytene chromosomes. The enzyme was found at many sites distributed throughout the genome in a pattern clearly distinct from that observed for histone H1, but it was especially concentrated in puffs induced by heat shock.     

The mechanism of electrical breakdown in the membranes ofValonia utricularis

Summary The dielectric breakdown in the membranes of cells ofValonia utricularis was investigated using intracellular electrodes and 500-sec current pulses. Electrical breakdown, which occurs when the membrane potential reaches a well-defined critical value, is not associated with global damage to the cell or its membranes (the membrane reseals in <5 sec). It was thus possible to investigate the effect of temperature on dielectric breakdown in single cells. It was found that the critical potential for breakdown was strongly dependent on temperature, decreasing from 1000 mV at 4°C to 640 mV at 30°C. The decrease in the breakdown potential with increasing temperature and the very short rise-time of the breakdown current (1 sec) suggests that the Wien field dissociation does not play a major role in the breakdown process. It is shown that the nonlinearI–V characteristics observed at different temperatures can be accurately accounted for with no adjustable parameters, by considerations of the mechanical compression of the membrane due to stresses induced by the electric field. Electrical breakdown on this scheme results from an electromechanical instability in the membrane. On this basis the present results indicate that the elastic modulus of the region of the membrane where breakdown occurs, decreases by a factor of 2 with increasing temperature from 4 to 30°C. On the assumption of a thickness of 4.0 nm and a dielectric constant of 5, the elastic modulus is estimated to have a value of 5×10⁶ Nm^–2 at 20°C.