Insights into the membrane proteome of rat liver peroxisomes: microsomal glutathione-S-transferase is shared by both subcellular compartments

Peroxisomes are ubiquitous "multipurpose" organelles of eukaryotic cells. Their matrix enzymes catalyze mainly catabolic and anabolic reactions of lipid metabolism, thus contributing to the regulation of lipid homeostasis. Since most metabolites must be actively transported across the peroxisomal membrane and since individual proteins and protein complexes play functional roles in such transport processes, we analyzed the peroxisomal membrane proteome. Benzyldimethyl-n-hexadecylammoniumchloride (16-BAC)/SDS-2-D-PAGE and mass spectrometry were used to characterize the proteomes of highly purified "light" and "heavy" peroxisomes of rat liver obtained by density gradient centrifugation. In both populations, the major integral membrane proteins could be detected in high concentrations, verifying 16-BAC/SDS-2-D-PAGE as a suitable tool for the preparation of membrane proteomes destined for mass spectrometric analysis. Both reliable and reproducible detection of a distinct set of microsomal (ER) membrane proteins, including microsomal glutathione-S-transferase (mGST), in light and heavy peroxisomal fractions was also possible. Compared with the abundance of most microsomal membrane proteins, we found mGST to be specifically enriched in peroxisomal membrane fractions. Furthermore, C terminus epitope-tagged mGST versions were localized at least in part to peroxisomes in different mammalian cell lines. Taken together, these data suggest that the peroxisomal GST is not a mere ER-contaminant, but a bona fide protein comprising the membrane proteome of both intracellular compartments. In addition, we could detect several mitochondrial proteins in light peroxisome fractions. This finding may likely indicate a physical association of light peroxisomes with mitochondria, since the organelles could be partly separated by mechanical stress. Whether this association is of functional importance awaits further investigation.     

Urocystis junci on Juncus balticus - first find in Sweden but is it rare?

The first find in Sweden of the smut Urocystis junci on Juncus balticus was made along the Bothnian sea coast. Of 18 surveyed populations of J. balticus along a 100 km coastal stretch, the smut fungus U. junci was found in ten. The distribution and the rarity of U. junci on J. balticus is discussed.     

A method to record circadian plant movements, with application to Oxalis leaf rhythms

A transducer was developed to record the circadian movement of the individual leaflets in Oxalis regnellii Mig. The method can easily be adapted to measure other kinds of plant movements as well. It is based on the detection of the shadow each leaflet casts on the small side of a specially formed Perspex plate. The light is guided through the Perspex and collected by a phototransistor, which provides an electrical signal that is proportional to the light intensity falling onto it. The output signal can be made a linear function of the leaf angle. This equipment was used in experiments to study the coupling between the 3 leaflets in Oxalis . Pulses of 4 h of red light were given to one of the leaflets, the two others were shielded from the light. A phase response curve was determined for each leaflet, but there was no significant difference in the phase response between the 3 leaflets. Experiments were also made in which the 3 leaflets were separated physically by cuts along the petiole between the pulvini. In this case ultradian oscillations were observed.     

Lithium ions lengthen the circadian period of growing cultures of the diatom Skeletonema costatum

Turbidity measurements revealed that the circadian rhythm in the growth rate of the marine diatom Skeletonema costatum (Greville) Cleve was insensitive to temperature between 5 and 22°C. Growth of the alga was inhibited by lithium ions at concentrations higher than 2 m M . Lengthening of the circadian period was observed in the presence of 0.5–1.5 m M Li⁺. The results indicate that the lithium effect generally observed on circadian rhythms should not necessarily be ascribed to changes in an intercellular coupling of cellular oscillators.     

The effect of summer feeding on juvenile arctic fox survival - a field experiment

The arctic fox Alopex lagopus L population in Sweden is small and its numbers fluctuate widely with food availability, l e rodent populations This fluctuation is mediated through differences in recruitment rates between years The recruitment can be divided into three phases number of litters born, number of cubs per litter and cub survival rates The number of litters and their sizes have been shown to depend on food availability during winter and spring To examine cub survival during the summer and how it relates to food availability, we conducted a feeding experiment m northern Sweden during 1990, a year of low rodent density, involving six occupied arctic fox dens Feeding at dens lowered cub mortality rates However, condition and growth rates of juveniles were not influenced by supplementary feeding at dens, nor were they related to the probability of survival for an individual Thus arctic foxes seem to minimize risks rather than maximize growth The juvenile mortality from weaning and over the next 6 wk was 21%, mostly due to starvation Only 82% survived from weaning to the first breeding season Of the one-year-old foxes, 50% survived their second year Supplementary feeding of juveniles had no effect on the final survival rates over these two years However, the immediate, positive effect on cub survival could be used in a long-term, extensive management programme if combined with winter feeding     

Effects of patch size and density on flower visitation and seed set of wild plants: a pan-European approach

1.  Habitat fragmentation can affect pollinator and plant population structure in terms of species composition, abundance, area covered and density of flowering plants. This, in turn, may affect pollinator visitation frequency, pollen deposition, seed set and plant fitness.
2.  A reduction in the quantity of flower visits can be coupled with a reduction in the quality of pollination service and hence the plants' overall reproductive success and long-term survival. Understanding the relationship between plant population size and/or isolation and pollination limitation is of fundamental importance for plant conservation.
3.  We examined flower visitation and seed set of 10 different plant species from five European countries to investigate the general effects of plant populations size and density, both within (patch level) and between populations (population level), on seed set and pollination limitation.
4.  We found evidence that the effects of area and density of flowering plant assemblages were generally more pronounced at the patch level than at the population level. We also found that patch and population level together influenced flower visitation and seed set, and the latter increased with increasing patch area and density, but this effect was only apparent in small populations.
5.   Synthesis. By using an extensive pan-European data set on flower visitation and seed set we have identified a general pattern in the interplay between the attractiveness of flowering plant patches for pollinators and density dependence of flower visitation, and also a strong plant species-specific response to habitat fragmentation effects. This can guide efforts to conserve plant–pollinator interactions, ecosystem functioning and plant fitness in fragmented habitats.     

Peroxisomes are present in murine spermatogonia and disappear during the course of spermatogenesis

Peroxisomes are organelles that are almost ubiquitous in eukaryotic cells. They have, however, never been described in germ cells within the testis. Since some peroxisomal diseases like Adrenoleukodystrophy are associated with reduced fertility, we have re-investigated the peroxisomal compartment of the germinal epithelium of mice using in situ hybridization, immunohistochemistry, Western blotting and immunoelectron microscopy. Within the seminiferous tubules, peroxisomes are present in Sertoli cells and in germ cells. We could show that small-sized peroxisomes of typical ultrastructure are concentrated in spermatogonia and disappear during the course of spermatogenesis. Peroxisomes of spermatogonia differ in their relative protein composition from previously described peroxisomes of interstitial cells of Leydig. Since germ cells differentiate in mouse testis in a synchronized fashion, the disappearence of peroxisomes could be a suitable model system to investigate the degradation of an organelle as part of a physiological differentiation process in higher eukaryotes.     

Density-dependent inhibition of 2-deoxy-d-glucose uptake into glioma and neuroblastoma cells in culture

The transport of 2-deoxy-d-glucose (2-DG) into cultured human glioma (138 MG) and mouse neuroblastoma (C1300) cells has been studied in relation to the growth curves of the cells. An initial increase in the uptake of 2-DG into exponentially growing 138 MG cells, could be attributed to the number of days the cells were kept in culture rather than to their increased density. As the 138 MG cells reached confluency after 3 days the 2-DG uptake became density-dependent inhibited. In still denser cultures the cell growth was inhibited. This was accompanied by morphological ‘normalization’ of the cells and increased uptake of 2-DG. Uptake of 2-DG into C1300 cells was density-dependent inhibited throughout the cell growth cycle. As the cell density increased from 15 × 10³ to 130× 10³ cells/cm² the rate of uptake/cell decreased to one-fourth. At the latter cell density the cells entered stationary phase, without any major changes in morphology. The results suggest that spontaneously occurring tumour cells, such as glioma and neuroblastoma cells, can regulate the sugar transport in relation to cell density. This could be due to newly-acquired differentiated properties of the cells or to true contact-inhibitory phenomena.     

Adaptation to an acid environment in Chironomus riparius (Diptera, Chironomidae) from Smoking Hills, NWT, Canada

The Smoking Hills in the North West Territories, Canada have burnt for centuries causing long term acidification of ponds in the vicinity. Chironomus riparius , a red chironomid larva dominated the bottom fauna in the ponds. It was investigated if it was the buffering capacity of the hemolymph rather than the oxygen binding capacity of its hemoglobin that gave these larvae a selective advantage and explained their high abundance. Canadian C. riparius larvae were compared with larvae of the same species from Sweden and with larvae of Chironomus plumosus and C. anthracinus also from Sweden. The Canadian strain of C. riparius survived 7 d exposure to pH 3.5 much better than the others. Titration curves on the hemolymph showed that the Canadian larvae had the highest buffering capacity. Within the pH range 6.0–7.0 it was 17–18 meq pH⁻¹ 1⁻¹ as compared with 13–15 meq pH⁻¹ 1⁻¹ for the others. The hemoglobin content of the Canadian larvae was found to be twice as high as that of the same species from Sweden.     

Age of inoculum strongly influences persister frequency and can mask effects of mutations implicated in altered persistence

The majority of cells transferred from stationary-phase culture into fresh medium resume growth quickly, while a few remain in a nongrowing state for longer. These temporarily nonproliferating bacteria are tolerant of several bactericidal antibiotics and constitute a main source of persisters. Several genes have been shown to influence the frequency of persisters in Escherichia coli, although the exact mechanism underlying persister formation is unknown. This study demonstrates that the frequency of persisters is highly dependent on the age of the inoculum and the medium in which it has been grown. The hipA7 mutant had 1,000 times more persisters than the wild type when inocula were sampled from younger stationary-phase cultures. When started after a long stationary phase, the two displayed equal and elevated persister frequencies. The lower persister frequencies of glpD, dnaJ, and surA knockout strains were increased to the level of the wild type when inocula aged. The mqsR and phoU deletions showed decreased persister levels only when the inocula were from aged cultures, while sucB and ygfA deletions had decreased persister levels irrespective of the age of the inocula. A dependency on culture conditions underlines the notion that during screening for mutants with altered persister frequencies, the exact experimental details are of great importance. Unlike ampicillin and norfloxacin, which always leave a fraction of bacteria alive, amikacin killed all cells in the growth resumption experiment. It was concluded that the frequency of persisters depends on the conditions of inoculum cultivation, particularly its age, and the choice of antibiotic.