Retinoic acid fails to induce differentiation in human teratocarcinoma cell lines that express high levels of a cellular receptor protein

Human embryonal carcinoma (EC) cells and other human teratocarcinoma-derived cells lines were not observed to differentiate in culture in response to retinoic acid. Nevertheless, they express high levels of a cellular binding protein (cRABP) which, in murine EC cells, appears to be necessary for the induction of differentiation by retinoic acid.     

Geomorphological features drive spatiotemporal dynamics of young-of-the-year brown trout populations in a large New Zealand river catchment

1. Determining the factors driving population dynamics of stream salmonids across broad landscapes is important for understanding stream ecosystem functioning and for the management and conservation of the populations of such fish. A few studies have described the determinants of the early life history of salmonids across catchments, but none of them have examined how this spatial variation develops temporally.
2. We hypothesised that: (1) spatiotemporal dynamics of young-of-the-year (YoY) trout populations vary within the catchment, with loss rates (emigration plus mortality) being higher in lower elevation, downstream reaches than in higher elevation, upstream ones; and (2) loss rate would be density dependent, leading to reduced intra- and inter-cohort competition and supporting establishment of resident populations.
3. We tested the first hypothesis by examining relationships between geomorphic characteristics of spawning streams and temporal dynamics of YoY brown trout density, loss rate and biological traits through an austral summer across the catchment of New Zealand's fourth-longest river, the Taieri River. To test the second hypothesis, we examined whether initial YoY density in spring and other biotic determinants affected loss rate and cohort structure dynamics, resulting in density-dependent self-thinning of YoY fish to avoid resource limitation.
4. Spring YoY density and subsequent loss rate was higher in low elevation sites, corresponding to stream accessibility to migratory spawners. These significant correlations of YoY density and related biotic variables with elevation disappeared later in the season, indicating that regardless of their origin, brown trout YoY tend to form stream resident populations with multicohort structure and densities low enough to limit intraspecific competition.
5. Our findings provide evidence that geomorphological features of the landscape affect temporal dynamics of YoY trout populations driven by density-dependent self-regulatory mechanisms that can control the abundance of growing fish.

     

Noncontact dipole effects on channel permeation. III. Anomalous proton conductance effects in gramicidin

Proton transport on water wires, of interest for many problems in membrane biology, is analyzed in side-chain analogs of gramicidin A channels. In symmetrical 0.1 N HCl solutions, fluorination of channel Trp(11), Trp-(13), or Trp(15) side chains is found to inhibit proton transport, and replacement of one or more Trps with Phe enhances proton transport, the opposite of the effects on K(+) transport in lecithin bilayers. The current-voltage relations are superlinear, indicating that some membrane field-dependent process is rate limiting. The interfacial dipole effects are usually assumed to affect the rate of cation translocation across the channel. For proton conductance, however, water reorientation after proton translocation is anticipated to be rate limiting. We propose that the findings reported here are most readily interpreted as the result of dipole-dipole interactions between channel waters and polar side chains or lipid headgroups. In particular, if reorientation of the water column begins with the water nearest the channel exit, this hypothesis explains the negative impact of fluorination and the positive impact of headgroup dipole on proton conductance.     

Scour and fill patterns in a New Zealand stream and potential implications for invertebrate refugia

1. The hyporheic zone has long been regarded as a potential refugium for lotic invertebrates during disturbance. However, there have been few attempts to quantify the stability of this habitat during high flow events. In a New Zealand stream with an unstable bed, the present authors monitored spatial patterns of scour and fill in a riffle in a wide flood plain and at two sites in a constrained reach: a pool-riffle with bedrock outcrops and a plane-bed (a bedform characterized by long stretches of planar stream bed). 2. At each 20-m site, 100 scour chains were installed in a systematic grid with about 1 m between chains. Scour was measured by comparing the length of chain exposed before and after a high flow event, whereas filling depth was equivalent to the thickness of the sediment deposited on top of the chains during the event. For each chain, the present authors noted dominant particle size and degree of packing of the surrounding bed, water depth and presence or absence of large stones upstream. Chains were re-located after four smaller spates, one intermediate event and one large flood. 3. Most events caused a complex mosaic of bed patches which experienced scour, fill or remained undisturbed. These patterns, which were mostly site- and event-specific, were often significantly influenced by the longitudinal or lateral position of the chains in the spatial grids. 4. The cumulative effect of the six high flow events differed substantially between sites. The first site experienced predominantly scour, the second both scour and fill, and the third almost exclusively fill. These differences were partly explained by channel geomorphology. The bedrock outcrops at the constrained pool-riffle site forced the flow at high discharge, causing deep scour in these areas, whereas a backwater effect at the third site reduced near-bottom shear stress during larger events and led to sediment deposition. 5. Except for a single event at the second site, scour affected mainly the uppermost 10–15 cm of the stream bed. Therefore, almost the entire hyporheic zone below this depth would have been available as refugium for invertebrates, in addition to the often consider-able number of bed patches which remained undisturbed during the six high flow events. 6. Fill without earlier scour during the same high flow event was common at all sites. Most previous studies have assumed that lotic invertebrates are mainly affected by scour during high flow events, but the consequences of sediment deposition may be just as far reaching.     

Das Gestaltproblem

Ohne Zusammenfassung     

Vergleichende Untersuchungen des Eiweiss-Haushalts beim Streckungswachstum von Blütenblättern und anderen Organen

Ohne ZusammenfassungMit 15 TextabbildungenDissertation der Mathematisch-Naturwissenschaftlichen Fakultät der Universität Bonn.