Zooplankton species composition in the Oosterschelde (SW Netherlands) before,during and after the construction of a storm-surge barrier

During the period of construction of a storm-surge barrier current velocities decreased strongly and the Eastern compartment of the basin obtained a lagoon-like character. The rotifer Synchaeta spp., already abundant in the neighbouring salt and brackish lakes, profited from this condition. Higher and less fluctuating salinities caused the estuarine character of this compartment to disappear in the post-barrier years. This was reflected in the obscured succession of some Acartia species: the estuarine A. tonsa dominated in pre-barrier- and barrier years during summer, while the marine A. clausi was abundant in the post-barrier Oosterschelde during that time. Also the changed food conditions (Bakker & Vink, 1993) may have played a role in this phenomenon.Further changes in species composition were hardly observed. The main changes were of a quantitative nature (Bakker & Van Rijswijk, 1993; Tackx et al., 1993). A list of the commonly occurring species is given.     

Naturally induced secretions of the potato cyst nematode co-stimulate the proliferation of both tobacco leaf protoplasts and human peripheral blood mononuclear cells.

Naturally induced secretions from infective juveniles of the potato cyst nematode Globodera rostochiensis co-stimulate the proliferation of tobacco leaf protoplasts in the presence of the synthetic phytohormones alpha-naphthaleneacetic acid (NAA) and 6-benzylaminopurine (BAP). With the use of a protoplast-based bioassay, a low-molecular-weight peptide(s) (< 3 kDa) was shown to be responsible for the observed effect. This mitogenic oligopeptide(s) is functionally dissimilar to auxin and cytokinin and, in addition, it does not change the sensitivity of the protoplasts toward these phytohormones. In combination with the mitogen phytohemagglutinin (PHA), cyst nematode secretions also co-stimulated mitogenesis in human peripheral blood mononuclear cells (PBMC). The stimulation of plant cells isolated from nontarget tissue--these nematodes normally invade the roots of potato plants--suggests the activation of a general signal transduction mechanism(s) by an oligopeptide(s) secreted by the nematode. Whether a similar oligopeptide-induced mechanism underlies human PBMC activation remains to be investigated. Reactivation of the cell cycle is a crucial event in feeding cell formation by cyst nematodes. The secretion of a mitogenic low-molecular-weight peptide(s) by infective juveniles of the potato cyst nematode could contribute to the redifferentiation of plant cells into such a feeding cell.     

The bactericidal action of streptomycin: membrane permeabilization caused by the insertion of mistranslated proteins into the cytoplasmic membrane of Escherichia coli and subsequent caging of the antibiotic inside the cells due to degradation of these proteins.

The mechanism by which the aminoglycoside antibiotic streptomycin permeabilizes the cytoplasmic membrane of Escherichia coli cells was reinvestigated. For this purpose, the extent of streptomycin-induced K+ loss from cells growing at low external K+ concentrations was taken as a measure of membrane permeabilization. Experiments with different K(+)-uptake mutants showed that the antibiotic specifically increased the passive permeability of the cell membrane to K+ and other ions. These permeability changes were small and the membrane potential of the treated cells remained high. The membrane permeabilization was not due to a direct interaction of the antibiotic with the cell membrane, since cells that carry an rpsL mutation and synthesize proteins in a streptomycin-insensitive way did not lose K+ after the addition of the antibiotic. Due to misreading and premature termination of translation the cells synthesized aberrant proteins under the conditions where membrane permeabilization occurred. Two conditions are described under which the cells both degraded these mistranslated proteins rapidly and reaccumulated K+, lending support to the hypothesis that membrane permeabilization is due to the presence of the mistranslated proteins in the cell membrane. Evidence is presented that the irreversibility of (dihydro)streptomycin uptake by cells washed free from the antibiotic might also be due to rapid degradation of the mistranslated proteins, leading to 'caging' of the antibiotic inside the cells.     

Intraspecific Trait Variation Driven by Plasticity and Ontogeny in Hypochaeris radicata

The importance of intraspecific variation in plant functional traits for structuring communities and driving ecosystem processes is increasingly recognized, but mechanisms governing this variation are less studied. Variation could be due to adaptation to local conditions, plasticity in observed traits, or ontogeny. We investigated 1) whether abiotic stress caused individuals, maternal lines, and populations to exhibit trait convergence, 2) whether trait variation was primarily due to ecotypic differences or trait plasticity, and 3) whether traits varied with ontogeny. We sampled three populations of Hypochaeris radicata that differed significantly in rosette diameter and specific leaf area (SLA). We grew nine maternal lines from each population (27 lines total) under three greenhouse conditions: ambient conditions (control), 50% drought, or 80% shade. Plant diameter and relative chlorophyll content were measured throughout the experiment, and leaf shape, root∶shoot ratio, and SLA were measured after five weeks. We used hierarchical mixed-models and variance component analysis to quantify differences in treatment effects and the contributions of population of origin and maternal line to observed variation. Observed variation in plant traits was driven primarily by plasticity. Shade significantly influenced all measured traits. Plant diameter was the only trait that had a sizable proportion of trait variation (30%) explained by population of origin. There were significant ontogenetic differences for both plant diameter and relative chlorophyll content. When subjected to abiotic stress in the form of light or water limitation, Hypochaeris radicata exhibited significant trait variability. This variation was due primarily to trait plasticity, rather than to adaptation to local conditions, and also differed with ontogeny.     

Levels of Organization in the Song of the Bobolink (Icteridae: Dolichonyginae)

By comparison with other icterids, the bobolink (Dolichonyx oryzivorus) sings an unusually long and complex song. The songs of four male bobolinks were analysed in terms of units at four different levels of analysis: the figure, the figure-sequence, the song-pattern, and the song. The different levels of analysis show different degrees of stereotypy and variation. Individual males in the study area differed in the frequency of use of the different song-patterns and in the way they assembled them into songs. Immediate repetition of song patterns within a song was unusual. Songs sung from fixed perches were shorter than songs sung in flight. The results suggest that the length of bobolink song is in part a consequence of its use of the song as a part of an elaborate flight display, and that the unit we called the “song-pattern” was closest to the unit designated “song” in most other species.     

Male mate choice scales female ornament allometry in a cichlid fish

Background  

Studies addressing the adaptive significance of female ornamentation have gained ground recently. However, the expression of female ornaments in relation to body size, known as trait allometry, still remains unexplored. Here, we investigated the allometry of a conspicuous female ornament in Pelvicachromis taeniatus, a biparental cichlid that shows mutual mate choice and ornamentation. Females feature an eye-catching pelvic fin greatly differing from that of males.     

Effect of cytosol fractions from lutropin-stimulated rat testes on pregnenolone production by mitochondria from normal rat testes

The rate limiting step in the production of steroids in the testis is the mitochondrial conversion of cholesterol to pregnenolone. This conversion can be stimulated by lutropin, but the precise interaction between lutropin-induced cytoplasmic factors and the mitochondrial activity in steroid production is as yet unknown. The results described in the present paper concern the steroid production of isolated mitochondrial fractions in recombination experiments with isolated supernatant fractions from total testes homogenates. Cyanoketone as well as SU-10603, an inhibitor of steroid 17α-hydroxylase activity are required to block pregnenolone metabolism. The results show that the cytoplasm contains lutropin-induced factor(s) which can exert its effect in vitro on the cholestorel side-chain cleavage activity in intact mitochondria isolated from control testes.     

An online catalogue of AFLP markers covering the potato genome

An AFLP marker catalogue is presented for gene mapping within cultivated potato. The catalogue is comprised of AFLP fingerprint images of 733 chromosome-specific AFLP markers which are mapped relative to 220 RFLP loci, isozyme loci, morphological characteristics and disease resistance traits. Use of the catalogue is based on identification of common AFLP markers which are visually recognized on autoradiogram images as co-migrating bands in fingerprints generated from different genotypes. Images of AFLP fingerprints combined with detailed information on the genomic location of all AFLP markers are available at URL: http://www.spg.wau.nl/pv/aflp/catalog.htm. It is demonstrated that the comparison of autoradiogram images and subsequent identification of common AFLP markers solely are efficient means for alignment of linkage groups and mapping target genes.     

Assignment of the gene coding for human peroxisomal 3-oxoacyl-CoA thiolase (ACAA) to chromosome region 3p22----p23

The chromosomal location of the human gene coding for peroxisomal 3-oxoacyl-CoA thiolase (ACAA) was determined with the aid of cDNA and genomic probes by screening of rodent x human somatic cell hybrids and in situ hybridization. The results localize the gene to chromosome region 3p22----p23.     

DNA restriction fragment length polymorphisms in differential diagnosis of genetic disease: application in neuromuscular diseases

Summary Three mutations causing alpha-1-antitrypsin defiiency have been identified by gene amplification and direct DNA sequencing. In the Pi (proteinase-inhibitor) null_cardiff gene, the codon for aspartate at position 256 has mutated to encode valine. In Pi M_malton and Pi I, the respective mutations are the deletion of the codon for a phenylalanine residue at position 51 or 52, and a single base substitution resulting in arginine being replaced by cysteine at position 39. Examination of the protein tertiary structure suggests that all of these mutations are likely to result in folding abnormalities that may explain the deficiency states.