Action Potentials in Lupinus angustifolius L. Shoots: III. DETERMINATION OF THE REFRACTORY PERIODS

The refractory periods for action potentials (AP) were investigatedin Lupinus shoots by application of pairs of electrical stimuli(d.c). The response (AP) for the second stimulus is characterized.The second response differs in amplitude, range, and propagationvelocity from the first, depending on the strength of the stimuliand the time interval between them. The absolute refractoryperiod determined on this basis lasts 12 min, and the relativeone from 12 to about 90 min. The character of the refractoryphenomenon is similar in the case of nerves, only the processesin Lupinus are 10³ to 10⁵ times slower. The possibility of transmission of excitation from cell to cellis discussed.     

Phylogenetic relationships and rate of early diversification of Australian Sphenomorphus group scincids (Scincoidea, Squamata)

The Australian Sphenomorphus group is a morphologically and ecologically diverse clade of lygosomine scincids, collectively comprising more than one‐half of the Australian scincid fauna. A previous phylogenetic analysis of mitochondrial 12S and 16S rRNA, and ND4 and adjacent tRNA sequences for a series of Australian Sphenomorphus group scincids recovered several well‐supported, major clades, although these were generally separated by relatively short branches associated with low support values. Applying a recently described methodology for inferring lineage‐level polytomies, I employ ATP synthetase‐β subunit intron sequences and the existing mitochondrial (mt)DNA data set (with sequences for additional taxa) to assess the hypothesis that the poorly resolved basal relationships within the Australian Sphenomorphus group are a consequence of the major clades having originated essentially simultaneously. Phylogenetic analyses of the separate mtDNA and intron sequence data reveal a number of congruent clades, including Anomalopus, Calyptotis, Ctenotus, Lerista, the Eulamprus quoyii group, the Glaphyromorphus crassicaudis group (including Glaphyromorphus cracens, Glaphyromorphus darwiniensis, and Glaphyromorphus fuscicaudis), Glaphyromorphus gracilipes + Hemiergis, Coeranoscincus reticulatus + Ophioscincus truncatus + Saiphos, and Eulamprus amplus + Eulamprus tenuis + Gnypetoscincus + Nangura. The relationships among these clades indicated by the two data sets, however, are generally incongruent. Although this may be partially ascribed to error in estimating phylogenetic relationships due to insufficient data, some incongruence is evident when uncertainty in inferred relationships is allowed for. Moreover, the congruent clades are typically separated by very short branches, several having a length insignificantly different from zero. These results suggest that initial diversification of Australian Sphenomorphus group scincids was rapid relative to the substitution rates of the mtDNA and intron fragments considered, if not essentially simultaneous. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 92 , 347–366.     

The Fabrication of H+-Selective Liquid-Membrane Micro-electrodes for Use in Plant Cells

The hydrogen ion-sensitive liquid-membrane micro-electrode,as described by Amman, Lanter, Steiner, Schulthess, Shijo, andSimon (1981) has been developed further and made applicablefor turgescent plant cells even with tough cell walls, by treatmentwith polyvinylchloride (PVC). Such an electrode is slower (t=5–10s) than the untreated electrode (t=2–6 s), but displays55–59 mV/pH-unit between pH 4·3 and 9·0,and is almost insensitive towards different buffers and K⁺.The electrodes are usable on more than one cell and have stillgood recalibration properties. Testing the electrodes on 11different cell types of Riccia fluitans, Sinapis alba, Zea mays,Avena sativa, Kalanchöe daigremontiana, Lemna gibba andChara corallina, we find the internal pH slightly alkaline (7·1–7·6)in ten cases (exception: old rhizoids of Riccia, pH₁=4·8).From that we conclude that the pH-electrode measures in thecytosol. According to the different plant material, severalprocedures for internal pH-measurements are presented and supportedby data: Application of cyanide and acetic acid causes internalacidification. Light-off transiently alkalinazes, light-on transientlyacidifies the internal pH. The advantages and limitations ofthe method are critically discussed, and it is concluded thatthis electrode is a powerful tool in plant physiology. Key words: Internal pH, pH-sensitive micro-electrode     

Breeding success and the question of clutch size of Northwestern Crows Corvus caurinus

The breeding biology of two island populations of the Northwestern Crow was studied in British Columbia over a period of five years. Both populations laid an average of four eggs per clutch, of which approximately 75% hatched. More young survived to fledge on Mandate than on Mitlenatch Island. The young from nests close (< 100 m) to the beach on Mitlenatch had a higher survival rate than those from further inland. The number of eggs lost or failing to hatch was lowest in clutches of four eggs. There was a non-significant trend for chick survival to be inversely related to clutch size. The net result was that clutches of five eggs produced no more young than did clutches of four eggs. It is suggested that the major limiting factor on clutch size is food availability but the decreased hatching success of any remaining eggs once hatching has started is also a contributing factor.     

Osmotic responses of unicellular blue-green algae (cyanobacteria): changes in cell volume and intracellular solute levels in response to hyperosmotic treatment

Abstract Changes in cell volume and solute content upon hyperosmotic shock have been studied for six unicellular blue-green algae (cyanobacteria): Synechococcus PCC 6301, PCC 6311; Synechocystis PCC 6702, PCC 6714, PCC 6803 and PCC 7008. The extent of change in volume was shown to be dependent upon the solute used to establish the osmotic gradient, with cells in NaCl showing a reduced shrinkage when compared to cells in media containing added sorbitol and sucrose. Uptake of extracellular solutes during hyperosmotic shock was observed in Synechocystis PCC 6714, with maximum accumulation of external solutes in NaCl and minimum solute uptake in sucrose solutions. Conversely, solute loss from the cells (K⁺ and amino acids) was greatest in sucrose-containing media and least in NaCl. The results show that these blue-green algae do not behave as ‘ideal osmometers’ in media of high osmotic strength. It is proposed that short-term changes in plasmalemma permeability in these organisms may be due to transient membrane instability resulting from osmotic imbalance between the cell and its surrounding fluid at the onset of hyperosmotic shock.     

The DNA of Acanthamoeba spp.; A Method for Extraction and Its Characterization

SYNOPSIS. A method is described which permits the recovery of a high yield of undegraded DNA from Acanthamoeba castellanii. The DNA of A. castellanii is comprised of 2 species: the buoyant density of the major component is 1.720 and of the minor component, 1.693. The renaturation characteristics of the minor component suggest that it is of mitochondrial origin. Two components are also present in the DNA of A. palestinensis, A. polyphaga and A. astronyxis. The buoyant densities of major and minor components differ between species.     

Reproductive strategy and the life cycle in graptoloid colonies

Urbanek, A. 1990 10 15: Reproductive strategy and the life cycle in graptoloid colonies. Lethaia , Vol. 23, pp. 333–340. Oslo. ISSN 0024–1164.
Graptoloid colonies were clones composed in all probability of hermaphroditic zooids. Their breeding system approaching that of amphicarpic plants, namely distant out crossing combined with selfing, was exceptionally flexible. Moreover, the balanced coexistence of these extreme means of reproduction may be visualized as an evolutionarily stable strategy (ESS). The evolutionary consequences of such a breeding system might have accounted for the overall high rates of graptoloid evolution as well as for the rapid transformations in large populations. Sexual reproduction of graptoloid colonies was complemented by a multiplication through occasional fragmentation of colonies and subsequent regeneration from the fragments. Fragmentation of colonies played an important role in the survival of graptoloid colonies during catastrophic events such as hurricanes and later in recruitment. Fragmentation followed by regeneration, and only later by sexual reproduction of regenerated fragments, constituted the so-called great cycle (GC), whereas the regular course of events initiated by sexual reproduction in an undisturbed (complete) colony resulted in normal colony formation (astogeny) and is termed the small cycle (SC). Thus the adaptive significance of the sexual process in the life cycle is in the restoration of the perfect' pattern of the complete colony, which offered the best hydrodynamic properties and highest fitness. ▭ Graptolithina, Graptoloidea, breeding sysfem, reproductive strategy, fragmentation, life cycle .     

Indirect effects of fish predation on calcite supersaturation, precipitation and turbidity in a shallow prairie lake

SUMMARY.

• 1 We tracked calcite saturation and seston composition during 1987 and 1988 in a shallow, hardwater prairie lake, 1 year before and 1 year after a lake-wide fish removal. We also measured the contribution of calcite to turbidity during 1988.
• 2 In both years calcite saturation increased rapidly after all ice had thawed and peaked during mid-late summer with the mineral saturation index of calcite (SI) sometimes exceeding 30.
• 3 Removal of calcite from lake seston by gentle acidification of unfiltered water samples showed suspended calcite to be an important source of lurbidity in this lake.
• 4 The lake-wide fish removal produced detectable changes in the annual cycle of calcite saturation and precipitation. Increased grazing by Daphnia galeata and Daphnia pulex apparently reduced calcite saturation during early summer by suppressing the phytoplankton, and lowering the demand for CO₂.
• 5 Lower calcite precipitation, as well as direct removal of calcite by Daphnia grazing, probably contributed to the improvement in water transparency observed after the fish kill.