How important is the crustacean plankton for the maintenance of water clarity in shallow lakes with abundant submerged vegetation?

• 1 We measured the abundance and biomass of filter‐feeding microcrustacean zooplankton and calculated their grazing impact on phytoplankton biomass during summer in five shallow, mesotrophic to eutrophic lakes. For three of the lakes data exist both from years with dense submerged vegetation and low turbidity (the clearwater state), as well as from years characterised by sparse vegetation and high turbidity (the turbid state). In the other two lakes data are available only for clearwater conditions.
• 2 In all lakes conditions of dense vegetation and clear water coincided with a low abundance of crustacean plankton during summer. In the three lakes that shifted, the calculated biovolume ingested by crustacean plankton (filtering rate) was 3–11 times lower during clearwater conditions compared with turbid conditions. Because phytoplankton biomass was lower during clearwater conditions, however, daily grazing pressure from microcrustacea (expressed as percentage of phytoplankton biomass) did not differ between states. In three of the five lakes, grazers were estimated to take less than 10% of the phytoplankton biomass per day, indicating filtration by zooplankton was not the most important mechanism to maintain clearwater conditions.
• 3 High densities of Cladocera were found in three of the lakes within dense stands of Charophyta. However, these samples were dominated by plant‐associated taxa that even during the night were rarely found outside the vegetation. This indicates that plant‐associated zooplankton has no major influence on the maintenance of water clarity outside the vegetation.
• 4 Spring peak abundance of Cladocera was observed in three of the lakes. In two of these, where seasonal development was studied in both the clearwater and the turbid state, spring peaks were lower during the clearwater state.
• 5 Predation, low food availability or a combination of both may explain the low zooplankton densities. Phytoplankton may be limited by low phosphorus availability in the lakes dominated by Charophyta. Our results indicate that the importance of zooplankton grazing may have minor importance for the maintenance of the clearwater state in lakes with dense, well‐established submerged vegetation.

     

Seasonal changes in cell‐mediated immunocompetence and mass gain in nestling barn swallows: a parasite‐mediated effect?

Reproduction in seasonal environments is usually timed so peak demand for food by offspring coincides with peak availability. Hence, late breeders will encounter a scarcity of food. Since parasite populations grow during the reproductive season of their hosts, late reproducing animals will also face an increasing challenge by parasites. We hypothesised that seasonal decrease in food availability and seasonal increase in parasite abundance will cause a trade-off between growth and immune function. This prediction was tested in nestling barn swallows ( Hirundo rustica ) from first and second broods. Nestlings from second broods mounted stronger T cell mediated immune responses to a challenge with a novel antigen, but had lower rates of mass gain, than nestlings from first broods, consistent with the prediction. Broods in which at least one nestling died had lower levels of T cell mediated immune response, but not lower rates of mass gain, than broods without mortality, suggesting that brood reduction is mediated through an inability of offspring to defend themselves against parasites rather than an inability to grow. Possible mechanisms include scarcity of specific nutrients needed for immune responses, and/or parasites being concentrated on a single or few nestlings.     

Phosphorylase a and Labile Metabolites During Anoxia: Correlation to Membrane Fluxes of K+ and Ca2+

The objective of the present study was to explore mechanisms responsible for activation of ion conductances in the initial phases of brain ischemia, particularly for the early release of K+ that precedes massive cell depolarization, and rapid downhill fluxes of K+, Na+, Cl-, and Ca2+. As it has been speculated that a K+ conductance can be activated either by an increase in the free cytosolic calcium concentration (Ca2+i) or by a fall in ATP concentration, the question arises whether the early increase in extracellular K+ concentration (K+e) is preceded by a rise in Ca2+i and/or a fall in ATP content. In the present experiments, ischemia was induced in rats by cardiac arrest, the time courses of the rise in K+e and cellular depolarization were determined by microelectrodes, and the tissue was frozen in situ through the exposed dura for measurements of levels of labile metabolites. including adenine nucleotides and cyclic AMP (cAMP), after ischemic periods of 15, 30, 60, and 120 s. Conversion of phosphorylase b to a was assessed, because it depends, among other things, on changes in Ca2+i. The K+e value rose within a few seconds following induction of ischemia, but massive depolarization (which is accompanied by influx of calcium) did not occur until after approximately 65 s. Activation of phosphorylase was observed already after 15 s and before glycogenolysis had begun. At that time, 3',5'-cAMP concentrations were unchanged, and total 5'-AMP concentrations were only moderately increased. The results demonstrate that a K+ conductance is activated at a time when the overall ATP concentration remains at 95% of control values.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Using Lanthanum,Neodymium, and Thorium as Conservative Indexing Elements to Indicate Soil Lead Deposition

A critical need exists for data evaluation protocols to determine if heavy metal deposition has impacted soil or sediment. For routine reconnaissance these protocols need to be analytically precise and affordable, two issues lacking in many regions. We employed a low-cost, commercially available aqua regia digestion procedure and developed a simple protocol for isolating pristine soil horizons and conservative indexing elements to compare to more Pb impacted soil horizons. Strongly Pb impacted soil horizons are easy to ascertain; however, moderately to slightly Pb impacted soils are more problematic to identify because of the natural Pb variation in soils. Using the harmonic mean of the soil concentrations of Lanthanum (La) and Neodymium (Nd) and also the soil concentrations of Thorium (Th) as conservative indexing elements, we were able to discriminate pristine soils from slightly to moderately Pb impacted soils. Ro values are estimators of elemental gain and loss, with Ro values greater than unity implying Pb addition, providing the comparative loss of other elements or biocycling are substantial contributing factors. All pedons known to have received Pb from atmospheric addition exhibited Ro values appreciably greater than unity, whereas soils known to be not impact or at most minimally impacted showed Ro values near unity. Commercially available and relative low cost aqua regia digestion analysis provided the analytical data for Pb, Fe, La, Nd and Th.     

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.     

Short cationic antimicrobial peptides bind to human alpha‐1 acid glycoprotein with no implications for the in vitro bioactivity

Several drugs interact with the major plasma proteins serum albumin and alpha‐1 acid glycoprotein. Such binding may be either beneficial or disadvantageous from a pharmacokinetic perspective. In the present paper, we investigate the thermodynamics involved in the binding of a series of promising cationic antimicrobial peptides to the alpha‐1 acid glycoprotein using isothermal titration calorimetry. The drug‐like peptides are able to effectively destroy multiresistant bacterial strains, and members of this peptide class are currently in clinical phase II trials. Similar peptides, in a previous study, have been shown to bind to serum albumin resulting in a 10‐fold reduction in the peptides ability to kill bacteria in vitro. Here, it is shown that the peptides also are ligands for alpha‐1 glycoprotein with moderate binding affinities. The binding mode is investigated in detail using molecular docking, which maps the interaction to sub‐pockets I, II and III of the binding site. Despite this interaction, protein binding is shown to have little or no effect on the ability of the peptides to kill bacteria in vitro, either at normal physiological or acute phase concentrations. The results show that although the peptides interact with the binding pocket of alpha‐1 acid glycoprotein, the low stoichiometric binding ratio ensures that the interaction is not an obstacle for further development of these promising peptides as antimicrobial therapies. Copyright © 2013 John Wiley & Sons, Ltd.     

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.