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     

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 .     

TRANSPORT OF GLUTATHIONE S-CONJUGATES IN THE YEASTSSACCHAROMYCES CEREVISIAE

Transport of 2,4-dinitrophenyl-S-glutathione (DNP-SG) and a fluorescent glutathione S-conjugate, bimane-S-glutathione (B-SG) was studied in the baker's yeasts (S. cerevisiae). Both conjugates were exported from the cells; the transport was inhibited by fluoride and vanadate like in mammalian cells. B-SG was also found to be accumulated in the vacuoles. The transport rate of DNP-SG outside the cell was higher in a vacuolar-deficient strain. A significant ATP-dependent uptake of (³H)-DNP-SG by vacuoles was found. These results indicate thatS. cerevisiaetransport glutathione S-conjugates both outside the cells and into the vacuoles.     

Influence of sampling strategy on the relationships between fauna and vegetation structure,plant lifeform and floristics

The effect of sampling strategy on animal-habitat relationships was evaluated with data collected from a 50 ha area containing a sequence of tropical vegetation types. Sampling sites were located randomly within defined habitat types (i.e. stratified random sampling) and systematically irrespective of habitat type. At each site the fauna, comprising birds (63 species), reptiles (15 species), amphibia (13 species) and grasshoppers (32 species) were sampled for the abundance of species. Simultaneously, vegetation and related data, comprising vertical structure (52 attributes), ground surface condition (18 attributes), plant lifeform (18 attributes) and the abundance of plant species (200) were recorded. Random and systematic data matrices, comprising sites defined by animal or vegetation attributes, were reduced dimensionally by correspondence analysis. Animal first dimension vectors were then regressed on the first dimension vectors of vegetation structure, lifeform and floristics, respectively. With stratified random sampling, vegetation structure (comprising vertical and ground attributes) and lifeform explained most of the variation in the fauna; floristics were not a significant factor. On the other hand with the systematic data, fioristics explained almost all of the variation in animal abundance and distribution. By removing the ecotonal sites from the systematic data set and recalculating vectors, the animal—vegetation relationships became similar to those generated from the stratified random sampling data. Clearly, the sampling strategy employed in a faunal survey has a major influence on the inventory of species, and on the relative importance of vegetation structure, lifeform and floristics in explaining animal distribution. The presence of ecotones in the systematic data set was highlighted as the key to the difference between the sampling strategies.     

Character selection in relation to the numerical taxonomy of some male Diaspididae (Homoptera: Coccoidea)

A quantitative comparison of the classifications of 24 species of male Diaspididae by principal component and principal coordinate analysis was extended to allow the comparison of classifications based on selected subsets of the 101 available characters. It was shown that subsets of 25–28 characters could be chosen numerically and used to construct classifications that resembled very closely the classification based on the reference set of characters. The conclusions are discussed in relation to other views on character-weighting and in relation to classifications of the Diaspididae based on traditional taxonomic characters provided by the females.