Insertion elements in Staphylococcus intermedius

Staphylococcus intermedius cultures from dogs, pigeons, horses and mink were investigated for the prevalence of the insertion elements IS 256 and IS 257 in relation to their antibiotic resistance. Copies of IS 256 could not be detected in any of the Staph. intermedius isolates tested whereas single copies of IS 257 occurred in the isolates from dogs and horses. The mink strains did not harbour IS 257 elements, whereas Staph. intermedius isolates from pigeons carried multiple copies of IS 257 as predicted from the hybridization patterns obtained with a gene probe derived from the internal part of the IS 257 -encoded transposase gene. Independently of the origin of the Staph. intermedius isolates, all IS 257 copies were found to be located in the chromosomal DNA. The large number of chromosomal IS 257 copies in the pigeon strains might help to explain chromosomal multiresistance in many of those strains.     

Nutritional, growth, and reproductive responses of maize (Zea mays L.) to arbuscular mycorrhizal inoculation during and after drought stress at tasselling

The effects of root colonization by the arbuscular mycorrhizal (AM) fungus Glomus intraradices Schenck & Smith on nutritional, growth, and reproductive attributes of two tropical maize cultivars with different sensitivities to drought were studied. Freshly regenerated seeds of selection cycles 0 (cv. C0, drought-sensitive) and 8 (cv. C8, drought-resistant) of the lowland tropical maize population "Tuxpeño sequía" were used in this greenhouse experiment. Maize plants were subjected to drought stress for 3 weeks following tasselling (75–95 days after sowing) and rewatered for the subsequent 5 weeks until harvest. Mycorrhizal (M+) plants had significantly higher uptake of N, P, K, Mg, Mn, and Zn into grain than non-mycorrhizal (M–) plants under drought conditions. AM inoculation also produced significantly greater shoot masses in C0 and C8 regardless of the drought-stress treatment. In the sensitive cultivar C0, drought stress reduced the shoot mass and grain yield by 23% and 55%, respectively, when roots were not colonized, while the reductions were only 12% and 31%, respectively, with mycorrhizal association. In addition, the emergence of tassels and silks was earlier in M+ plants than in M– plants under drought conditions. Mycorrhizal response was more pronounced under both well-watered and drought conditions in C0 than in the C8 cultivar. The overall results suggest that AM inoculation affects host plant nutritional status and growth and thereby alters the reproductive behaviour of maize under drought conditions.     

The importance of intraspecific competition in a Littorina littorea population in the Wadden Sea

Two field experiments were carried out totest whether effects of intraspecific competition ina Littorina littorea population can be detectedin a short-term investigation. Different size classesof L. littorea showed no significant differencein preferences when offered four kinds of eitherpossible food or substrata (Fucus vesiculosus,Ulva lactuca, Carcinus maenas, brick).Large and medium winkles preferred Fucusvesiculosus, followed by Ulva lactuca. Deadshore crabs (Carcinus maenas) were the leastpreferred objects for all size classes. On the firstday of the experiment bricks were more attractive tosmall littorines than to larger ones. Considering allfour days, the same ranking occurred for all sizeclasses: Fucus vesiculosus > Ulvalactuca > brick > Carcinus maenas. The reactionofjuveniles to increased densities was examined using anin situ caging experiment on a mussel bed. Meshsize of the cages allowed adult densities to beincreased while juveniles could escape by passingthrough the meshes. However, there was no significantemigration of small winkles even from cages with 10 to20 times natural density of large individuals. Ofgreater importance was the original number of winklesat the site. The available resources on the musselbeds appear to be sufficient to maintain a highpopulation density. Intraspecific competition does notseem to play a major role in this L. littorea-population.     

Ataxia with Vitamin E Deficiency: Refinement of Genetic Localization and Analysis of Linkage Disequilibrium by Using New Markers in 14 Families

Ataxia with vitamin E deficiency (AVED) is an autosomal recessive disease characterized clinically by neurological symptoms with often striking resemblance to those of Friedreich ataxia. This disorder has been reported previously as familial isolated vitamin E deficiency. We have mapped recently the AVED locus to a 5-cM confidence interval on chromosome 8q by homozygosity mapping in six Mediterranean families. We have now analyzed six new and two previously described families and demonstrate genetic homogeneity despite important clinical variability and wide geographic origins. Analysis of nine new tightly linked microsatellite markers, including four characterized in this study, revealed a predominant but not unique mutation in northern African populations, where this condition is more frequent. Haplotype analysis but also classical recombinations allowed us to refine the AVED position to a 1-cM interval. A YAC contig over this interval was constructed from marker STSs and YAC fingerprint data, in order to facilitate the search of the AVED gene.     

Glutamine synthetase (GS) expression is reduced in senile dementia of the Alzheimer type

Glutamine synthetase (GS), a metabolic marker of the mature astrocyte, was investigated in the temporal neocortex of postmortem brain samples of 8 cases, either not demented or affected by senile dementia of the Alzheimer type. A negative correlation between the GS protein level and the density of both classical A4 deposits and senile plaques was evidenced. Such a correlation for GS underlies a dysfunction of the astroglial metabolism and particularly of the glutamate and ammonia neutralization. Since GS is sensitive to oxidative lesioning, the changes in GS level that were observed, occurring at the posttranslational stage, might reflect oxidative damage and have severe consequences on the pathological cascade of events.     

Crystallization of the complex of human IFN-γ and the extracellular domain of the IFN-γ receptor

A complex of human interferon-γ (IFN- γ) with the soluble extracellular domain of the IFN- γ receptor α-chain (IFN-γ-R) has been crystallised. Crystals of the complex were grown using PEG 4000 as the precipitating agent in the presence of β-octyl glucoside. The receptor-ligand complex crystallizes in a monoclinic space group and diffracts to about 3.0 Å resolution. Isomorphous crystals have been obtained with complex containing selenomethionine and cysteine mutants of IFN-γ, which may facilitate the ongoing X-ray structure determination. © 1995 Wiley-Liss, Inc.     

Influence of arbuscular mycorrhizae on the metabolism of maize under drought stress

A greenhouse experiment was carried out to investigate the influence of the arbuscular mycorrhizal (AM) fungus (Glomus intraradices Schenck & Smith) on metabolic changes in tropical maize (Zea mays L.) under drought. Two cultivars, Tuxpeno sequia CO (drought sensitive) and C8 (drought resistant), were subjected for 3 weeks to water stress following tasselling (75–95 days after sowing). Fully expanded 7th or 8th leaves were sampled and assessed for levels of chlorophyll, sugars, proteins, and amino acids. Chlorophyll content was not altered either by water stress or the presence of mycorrhizae. Mycorrhizal plants (M+) had higher total and reducing sugars than nonmycorrhizal plants (M-) at the end of 3 weeks of the drought cycle. An increase in protein content was observed with drought stress in M + plants of the cultivar C0. Most of the amino acids showed a linear increase during the period of water stress in M+ and M- plants for both cultivars. Total amino acids increased by 40.6% and 43.7% in M- plants of C0 and C8, respectively. With the presence of AM fungus, amino acid levels increased by only 10.7% and 19.2% of leaf dry mass in C0 and C8, respectively. Alanine, asparagine, glutamine, and glycine accounted for 70% of the amino acid pool. Under drought, AM inoculation enabled the plants to retain considerable amounts of sugars and proteins, especially in the drought-sensitive cultivar C0. This may be of physiological importance in helping the plant to withstand moderate drought.     

Kinetics of the appearance of mRNA for light-harvesting chlorophyll a/b protein in polysomes of barley

Polysomes from dark-grown and illuminated barley seedlings were translated in cell-free systems. The translation products reacting with the antibody against the light-harvesting chlorophyll a/b protein (LHCP) were analyzed by polyacrylamide gel electrophoresis. It was found that, in addition to the precursor protein of LHCP, a product was obtained that co-migrated with the mature protein. Furthermore, the results show that the light-induced proly(A)RNA for LHCP is integrated into the polysomal complex without delay, indicating that the integration of LHCP into the membrane is controlled at a higher level of gene expression.     

Effects of nitrogen deficiency and light of high intensity onCryptomonas rufescens (Cryptophyceae)

Summary C.rufescens excystment, experimentally induced, corresponds to a general metabolism recovery of the cell, previously in a resting phase. The cytoplasm changes without any polarity, and organelles like gullet and flagella redifferentiate. The thylakoids develop mainly from the stored lipidic compounds which then disappear. Phycoerythrin immediately fills the intrathylakoidal lumen. Pigment synthesis seems closely associated with the development of membranes. The activated cell divides and the cyst wall breaks down. The destruction of the wall begins in the median layer and is followed by a mechanical rupture of the external and internal layers. Each germinative cyst releases two or four fully differentiated cells. There is an exact symmetry between excystment and encystment, all the transformations of theC. rufescens cell being reversible.