Tuning in to multiple predators: conflicting demands for shell morphology in a freshwater snail

1. We examined the response to chemical cues from fish and crayfish, two predators with contrasting feeding modes, and their single and combined effect on shell morphology in the freshwater snail Radix balthica. 2. Snails were subjected to four treatments: tench (Tinca tinca), signal crayfish (Pacifastacus leniusculus), a combination of tench and signal crayfish and no predators (control). Shell shape, crushing resistance and shell thickness were quantified. We also analysed whether shape or shell thickness contributes most to crushing resistance. 3. Chemical cues from the fish induced a rounder shell shape in R. balthica, a thicker shell and a higher crushing resistance, whereas crayfish chemical cues had no effect on shell morphology, shell thickness or crushing resistance. Shell shape contributed more to crushing resistance than shell thickness. 4. The combined predator treatment showed an intermediate response between the fish and crayfish treatments. Shell roundness was reduced compared with the fish treatment, but the reduced crushing resistance that comes with a less rounded shell was compensated by an increased investment in extra shell material, exceeding that of the fish treatment. 5. Our study extends previous studies of multipredator effects on phenotypically plastic freshwater snails by showing that the snails are able to fine‐tune different elements of morphology to counter predator‐specific foraging modes.     

Pharmacological elevation of endogenous kynurenic acid levels activates nigral dopamine neurons

Summary. Inhibitors of kynurenine 3-hydroxylase have previously been used to increase endogenous levels of kynurenic acid, an excitatory amino acid receptor antagonist. In the present electrophysiological study PNU 156561A was utilized to elevate endogenous concentrations of kynurenic acid and subsequent effects on the firing pattern of dopamine (DA) neurons of rat substantia nigra (SN) were analyzed. Pretreatment with PNU 156561A (40 mg/kg, i.v., 5–7 h) caused a five-fold increase in endogenous kynurenic acid levels in whole brain five to seven hours after administration and also evoked a significant increase in firing rate and bursting activity of nigral DA neurons. The results of the present study show that a moderate increase in endogenous kynurenic acid levels produces significant actions on the tonic glutamatergic control of the firing pattern of nigral DA neurons, and implicate kynurenine 3-hydroxylase inhibitors as novel antiparkinsonian agents. Received April 3, 2000 Accepted July 2, 2000     

Intravital lectin perfusion analysis of vascular permeability in human micro- and macro- blood vessels

We previously applied intravital lectin perfusion in mouse models to elucidate mechanisms underlying vascular permeability. The present work transfers this technique to human models, analysing vascular permeability in macro- and microvessels. Human vascular endothelial surface carbohydrate biochemistry differs significantly from its murine counterpart, lacking alpha-galactosyl epitopes and expressing the L-fucose moiety in the glycocalyx; the poly-N-lactosamine glycan backbone is common to all mammals. We examined extensively lectin binding specificities in sections and in vivo, and then applied the poly-N-lactosamine-specific lectin LEA and the L-fucose-specific lectin UEA-I in human intravital perfusions. Transendothelial transport differed in macrovessels and microvessels. In microvessels of adult human fat tissue, rectal wall and rectal carcinomas, slow transendothelial transport by vesicles was followed by significant retention at the subendothelial basement membrane; paracellular passage was not observed. Passage time exceeded 1 h. Thus we found barrier mechanisms resembling those we described previously in murine tissues. In both adult and fetal macrovessels, the vena saphena magna and the umbilical vein, respectively, rapid passage across the endothelial lining was observed, the tracer localising completely in the subendothelial tissues within 15 min; vesicular transport was more rapid than in microvessels, and retention at the subendothelial basement membrane briefer.     

Superoxide dismutase and peroxidase activities in drought sensitive and resistant barley (Hordeum vulgare L.) varieties

The effects of water deficit on relative water content (RWC), on the activity superoxide dismutase (SOD) and peroxidase (POX) from leaves of two drought-resistant barley strains (Hordeum vulgare L.) varieties (TOKAK-157/37 and 56000/MISC-233) and one sensitive (ERGINEL-90) were studied. In 21 day old seedlings, drought stress was initiated by withholding water and lasted for 12 days. Activity of SOD increased by the effect of drought treatments in the leaves of drought-resistant varieties TOKAK-157/37 and 56000/MISC-233 as compared to sensitive variety ERGINEL-90. The drought treatment resulted in a 418 % and 59 % increase in SOD activity in resistant varieties at the end of the 12^th day of experimental period. However, an increase in activity of SOD was not accompanied by an increase in activity of POX in drought-resistant TOKAK-157/37 and 56000/MISC-233 except on the 6^th day of drought treatment in 56000/MISC-233. In drought-sensitive variety, ERGINEL-90, POX activity did not change throughout drought period.     

Cytoplasmic effects on the tissue culture response of callus from winter wheat mature embryos

A simple and reliable method was established for the maintenance of a permanent stock of several Medicago truncatula genotypes selected from a general seed stock by their in vitro culture amenability and embryogenic capacity. In the first step, multiple shoots were induced from the cotyledon axillary meristem meristem of pre-germinated seeds in Murashige and Skoog medium supplemented with cytokinins (9.3 M zeatin, 22.2 M benzylaminopurine or 4.5 M thidiazuron). In the second step, the induced shoots were allowed to develop in growth-regulator-free medium. Benzylaminopurine at 22.2 M supported the best combination of shoot quality and number of shoots produced. Rooting of microshoots depended on the cytokinin used for shoot induction and was faster for zeatin-treated shoots. In this work a propagation system was devised where the addition of growth regulators was restricted to the induction phase therefore reducing the risks of epigenetic and somaclonal variation.     

The effects of magnesium, calcium and EDTA on slime production byStaphylococcus epidermidis strains

Effect of magnesium, calcium and EDTA on slime production by 15 slime-positive and 13 slime-negative Staphylococcus epidermidis strains isolated from various clinical specimens was determined. The slime production on tryptic soy broth was significantly enhanced after addition of 128 mumol/L Mg2+. Similarly, the addition of Ca2+ caused a significant increase in slime production of all tested strains when concentration of Ca2+ exceeded 64 mumol/L. In contrast, in the presence of EDTA the slime production by all strains was significantly reduced. Hence Ca2+ and Mg2+ increase slime production of S. epidermidis. This finding is important in the context of the pathogenesis of biomedical implant infections caused by S. epidermidis.     

Pitting corrosion inhibition of aluminum 2024 by Bacillus biofilms secreting polyaspartate or γ-polyglutamate

Pitting corrosion of aluminum 2024 in Luria Bertani medium was reduced by the secretion of anionic peptides by engineered and natural Bacillus biofilms and was studied in continuous reactors using electrochemical impedance spectroscopy. Compared to sterile controls, pitting was reduced dramatically by the presence of the biofilms. The secretion of a 20 amino acid polyaspartate peptide by an engineered Bacillus subtilis WB600/pBE92-Asp biofilm slightly reduced the corrosion rate of the passive aluminum alloy at pH 6.5; however, the secretion of gamma-polyglutamate by a Bacillus licheniformis biofilm reduced the corrosion rate by 90% (compared to the B. subtilis WB600/pBE92 biofilm which did not secrete polyaspartate or gamma-polyglutamate). The corrosion potential ( E(corr)) of aluminum 2024 was increased by about 0.15-0.44 V due to the formation of B. subtilis and B. licheniformis biofilms as compared to sterile controls. The increase of E(corr) and the observed prevention of pitting indicate that the pitting potential ( E(pit)) had increased. This result and the further decrease of corrosion rates for the passive aluminum alloy suggest that the rate of the anodic metal dissolution reaction was reduced by an inhibitor produced by the biofilms. Purified gamma-polyglutamate also decreased the corrosion rates of aluminum 2024.     

Phytosociological investigations of a Pinus pinea L. forest in the Eastern Mediterranean Region (K. Maraş – Turkey)

In this study the phytosociological structures of Pinuspinea L. forests occuring in K. Mara province in theeastern-mediterranean region have been investigated. The vegetation of theresearch area has been studied according to the Braun-Blanquet (1932) methodanda Gastridio ventricosi-Pinetum pineaeassociation has been recognised.     

Autoradiographische Untersuchungen zur Aminosäure-Inkorporation im Nukleolus

Zusammenfassung Die unter dem Einfluß von TAA vergrößerten Leberzell-Nukleolen der Ratte inkorporieren in wesentlichem Umfang H³-Phenylalanin, wobei die Einbaurate der markierten Aminosäure in direkter Abhängigkeit zur Größe des Kernkörperchens steht. Die Resultate erlauben somit den Schluß, daß einmal in der Nukleolarsubstanz eine Synthese höherer EW-Körper bzw. eine Neubildung von Ribonukleoproteiden erfolgt, und daß zum andern eine Korrelation zwischen der Größe des Nukleolus und seiner synthetischen Aktivität im Hinblick auf seine EW-Syntheserate existiert. Der Tatbestand, daß die nukleoläre SK-Dichte (SK-Zahl/²) in unserem Experiment schon bei sehr kurzen Versuchszeiten (5 min nach Injektion der markierten Aminosäure) im Mittel etwa gleich der karyoplasmatischen SK-Dichte, im Einzelfalle aber ganz wesentlich höher als die karyoplasmatische ist, spricht für unser Beobachtungsgut weitgehend gegen eine alleinige Migration markierten Materials aus dem Karyoplasma in den Nukleolus. Dementsprechend stellt der Nukleolus als Funktionseinheit betrachtet einen selbständigen EW-Syntheseort dar.Die Untersuchungen wurden im Institut für Medizinische Isotopenforschung der Universität Köln (Leiter: Prof. Dr. W. Maurer) durchgeführt.