The dual effect of internal tetramethylammonium ions on the open states of the sodium channel in the squid giant axon.

Voltage-clamp recordings of INa in squid axons dialysed with Cs or TMA, and bathed in low Na choline seawater, showed that, except close to threshold, the initial peak of fast-inactivating current was invariably decreased by TMA, whereas the non-inactivating current in the steady state was simultaneously increased. The results suggest that although TMA does not act directly on the movements of the voltage sensors that activate the sodium system, it blocks single-channel conductance in a voltage-dependent fashion in both the open states of the Na channel, while it has an entirely different type of action by increasing the probability of late openings in the steady state. Another difference between the two open states was that the sodium permeability coefficient had a Q10 of 1.8 in the initial open state, whereas in the steady state the effect of temperature was much smaller or even negative.     

The ecology of Black Guillemot Cepphus grylle grylle chicks in the Baltic Sea region: insights into their diet,survival, nest predation and moment of fledging

Capsule: The diet of Black Guillemot Cepphus grylle grylle chicks in the Baltic Sea region was dominated by Viviparous Eelpout Zoarces viviparus. Risk of nest predation by avian and mammalian predators was perceived to be low, and hatching and fledging success were high.

Aims: To gain insight into the ecology of nestling Black Guillemots in the Baltic Sea region to fill knowledge gaps and benefit its conservation.

Methods: Two island groups in the Baltic Sea were visited several times during the breeding season of 2014 and 2015 to monitor nestling survival and fledging. In addition, camera traps were used in 2014 to monitor prey brought to chicks by adults and record possible nest predation events.

Results: Hatching success was 0.89 and 0.73 in 2014 and 2015, respectively, and fledging success was very high (0.95 and 0.97). No incidences of avian or mammalian predation were observed. Chicks fledged at night between 32 and 38 days after hatching. Viviparous Eelpout made up 95% of the prey items brought to the chicks by adults.

Conclusions: The hatching rate and fledging rate of the Black Guillemot was high in our study region. Juveniles seemed highly dependent on the availability of eelpout. Changes in the abundance of this species may therefore have negative effects on chick survival.     

Zur genetik der 6-Phosphogluconatdehydrogenase (EC:1.1.1.44) bei Säugern

Zusammenfassung Das Enzym 6-PGD zeigt bei den verschiedensten Species einen genetisch gesteuerten Polymorphismus, der sich bei elektrophoretischer Darstellung in einer Variabilität des Isoenzymmusters äußert. Die Befunde bei den bislang untersuchten Säugern unter Einschluß des Menschen lassen sich formalgenetisch nach dem Modell: 1 Genlocus mit multipler Allelie interpretieren. Zur Prüfung der Frage, ob das Säugergenom einheitlich nur ein Gen für dieses Enzym enthält oder ob bei einzelnen Species eine Duplikation dieses Gens existiert, wurdene eine Anzahl Säuger verschiedener Ordnungen untersucht. In einer ersten Mitteilung wird hier über 6 verschiedene Species der Microtinae berichtet. Die Befunde sprechen durchweg für die Existenz von jeweils nur 1 Genlocus der 6-PGD. Bei Microtus oeconomus wurden 2 Allele an diesem locus nachgewiesen, bei Microtus ochrogaster 3 verschiedene Allele. Durch Familienuntersuchungen bei diesen beiden Species werden alle möglichen Kombinationen dieser Allele nachgewiesen.

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The genetics of 6-PGD (EC: 1.1.1.44) in various mammals I. Studies on 6 species of Microtinae, Rodentia. Isoenzyme polymorphism and family studies in Microtus oeconomus and Microtus ochrogaster

Summary The enzyme 6-PGD exhibits a genetically determined polymorphism which results in a variability of the isoenzyme pattern. In mammals so far examined the findings are to be interpreted according to the model of multiple alleles at one single gene locus. In order to test whether the mammalian genome is uniformly endowed with one single locus for this enzyme or whether a duplication of this locus is present in certain species, we examined various mammals of different orders. Our results in this first communication on 6 different Microtinae species are all in agreement with the assumption of a single 6-PGD locus. In Microtus oeconomus 2 alleles could be demonstrated and in Microtus ochrogaster 3 different alleles. Family studies performed with both species revealed the occurrence of all the expected combinations of these alleles.

     

The age-distribution of cell cycle populations in plant root meristems : Complex tissues

The durations of the mitotic cycle periods, the proportions of cells in each cycle period of the proliferative and nonproliferative populations, and the rates of cell progression from G1-S and from G2-M were used to characterize the cytokinetics in root meristems of four plant species. The observed age-distribution of cells in the cycle of each meristem was not comparable to either a theoretical exponential or uniform age-distribution. A more exact fit of the observed age-distributions with theoretical distributions was hindered by proliferative cells which halted temporarily in G1 and/or in G2 in relative proportions similar to the nonproliferative cells in the meristem. Moreover, the preponderant cycle period in which cells halted temporarily differed among the species observed: it was G1 in Helianthus and Triticum and G2 in Pisum and Vicia. The cell populations of these complex tissues can be subdivided kinetically into three types: (1) rapidly proliferating cells; (2) slowly proliferating cells that halt temporarily in G1 and/or in G2; and (3) nonproliferating cells that halt in G1 and/or in G2.     

Pea (Pisum sativum) cells arrested in G2 have nascent DNA with breaks between replicons and replication clusters

DNA fiber autoradiography and alkaline sucrose sedimentation of DNA of cultured pea-root cells (Pisum sativum) arrested in G2 by carbohydrate starvation demonstrated that nascent DNA molecules of replicon (16–27 × 10⁶ D) and apparent cluster (~330 × 10⁶ D) size were not joined. That the arrested cells were in G2 was confirmed by single-cell autoradiography and cytophotometry. In pea there are about 18 replicons per average cluster, 4.2 × 10³ clusters, and 7.7 × 10⁴ replicons per genome.     

Replication of the rRNA and legumin genes in synchronized root cells of pea (Pisum sativum): evidence for transient EcoR I sites in replicating rRNA genes

Summary The temporal pattern of replication of the rRNA and legumin genes differs in synchronized pea root cells. The relative number of rRNA genes replicated hourly during the first five hours of S phase ranges between 5 and 10 percent. In late S phase, during hours six through nine, the number of rRNA genes replicated increases reaching a maximum of about 25 percent at the ninth hour. Unlike the rRNA genes, the legumin genes have a wave-like pattern of replication peaking in early S phase at the third hour and again in late S phase at the eighth hour.Replicating rDNA, isolated by benzoylated naphthoylated DEAE-column chromatography, has EcoR I restriction sites that are absent in non-replicating rDNA sequences. The cleavage of these sites is independent of the time of rDNA replication. The transient nature of the EcoR I sites suggests that they exist in a hemimethylated state in parental DNA.The two Hind III repeat-size classes of rDNA of var. Alaska peas are replicated simultaneously as cells progress through S phase. Thus, even if the 9.0 kb and 8.6 kb repeat classes are located on different chromosomes, their temporal order of replication is the same.     

Measurement and prediction of digestibility of forage maize in The Netherlands

Results of digestibility trials on fresh and ensiled maize (aerial parts) were analysed and compared with laboratory data.

Digestibility of the organic matter of ears was almost constant at 84–85%. Digestibility of organic matter of stover showed great variation. Variation between animals in apparent digestibility of organic matter was greater for maize diets than for diets based on grass products. Most of the differences between animals were caused by differences in the digestion of cell walls. When the true digestibility of cell contents was assumed to be complete, endogenous excretion was, on average, only 7% with respect to organic matter intake, and seemed dependent on digestibility of organic matter.

Prediction of apparent digestibility was more accurate with digestibility in vitro than with crude fibre, although for maize silage, significant relationships were found between crude fibre content and digestibility of organic matter. Standard deviation of organic matter digestibility between lots of fresh and ensiled maize grown on commercial farms amounted to only about 1.2 –2%. As this was only twice the accuracy of digestibility in vivo with four animals, fixed values will be presented to farmers, possibly corrected for year, hybrid selection and cropping practice.