Effects of GABA antagonists,SR 95531 and bicuculline,on GABAA receptor-regulated chloride flux in rat cortical synaptoneurosomes

Synaptoneurosomes isolated from cerebral cortices of male Sprague-Dawley rats were used for studying GABA_A receptor-regulated chloride influx. The in vitro effects of GABA antagonists, SR 95531 (a pyridazinyl GABA derivative) and bicuculline, on pentobarbital-stimulated, muscimol-stimulated or flunitrazepam-enhanced, muscimol-stimulated chloride uptake were studied. The chloride uptake was determined at 30°C, for 5 sec. Pentobarbital and muscimol produced a maximal stimulation of chloride uptake in cortical synaptoneurosomes at 500 M and 50M, respectively. SR 95531 as well as bicuculline had no effect on the basal uptake of chloride. Whereas, SR 95531 (0.3–30 M) and bicuculline (0.1–100 M), when added 5 min before muscimol (50 M), produced a significant concentration-dependent inhibition of muscimol (50 M)-stimulated chloride uptake (IC₅₀ s of 0.89±0.11 M and 13.45±2.10M, respectively). In studies of the inhibitory effects of SR 95531 and bicuculline on pentobarbital (500 M)-stimulated chloride uptake, the IC₅₀ s were 0.81±0.12 M and 3.86±1.14 M, respectively. SR 95531 exhibited a more potent inhibitory effect than bicuculline on flunitrazepam-enhanced, muscimol-stimulated chloride uptake. The results revealed that SR 95531 has a more potent antagonistic effect than bicuculline on GABA_A-regulated chloride flux.     

Mercury distribution in estuarine environments from Argentina: the detoxification and recovery of salt marshes after 15 years

Total Hg contents from abiotic (surface sediments and suspendedparticulate matter) and biological (crabs, fishes and halophytes)compartments from Bahía Blanca estuary and Mar Chiquita CoastalLagoon, Argentina, have been monitored since the 1980's. At BahíaBlanca estuary, high Hg concentrations were recorded during the early1980's in surface sediments (0.34 ± 0.22 g/g) andsuspended particulate matter (0.19 ± 0.10 g/g). Fishspecies, Mustelus schmitti (0.89 ± 0.29 g/g), Paralichthys brasiliensis (0.85 ± 0.18 g/g) and Micropogonias furnieri (0.37 ± 0.11 g/g) also presentedhigh Hg concentrations. The large industrial nucleus located within theestuary has been identified as the main metal source for this environment.Hg contents from the same area during 1996–1998 were significantlylower: surface sediments (0.164 ± 0.023 g/g), suspendedparticulate matter (0.048 ± 0.0017 g/g), fish Micropogonias furnieri (0.13 ± 0.02 g/g) and crab Chasmagnathus granulata (0.334 ± 0.071 g/g). This trendof environmental detoxification is probably related with (i) thetechnological changes incorporated by the local industry, (ii) a mostadequate management of industrial effluents, and (iii) the removal ofgreat sediment volume by dredging and refill.During the 1980's Mar Chiquita Lagoon Hg concentrations reached 0.08± 0.01 g/g in surface sediments and 0.09 ±0.025 g/g in suspended particulate matter, and 0.14 ±0.04 g/g in the fish Basilichthys bonariensis and 0.22 ±0.08 g/g in Paralichthys brasiliensis, and 0.08 ±0.01 g/g in the crab C. granulata, Hg concentrations werelower than at Bahía Blanca. Remote Hg sources for this Coastal Lagoonand atmospheric and stream transport of Hg is proposed as major Hgsources, since no Hg point sources exists nearby. Mercury concentrationsrecorded in the 1996–1998 period were lower than those recorded inthe previous decade: surface sediments (0.019 ± 0.004 g/g), suspended particulate matter (0.030 ± 0.008 g/g), halophyte Spartina densiflora (0.013 ± 0.008 g/g) or crab C. granulata (0.011 ± 0.009 g/g).Both Hg bioaccumulation and biomagnification processes were verified inBahía Blanca estuary and in Mar Chiquita Coastal Lagoon. This apparentrecovery of both estuarine environments deserves to be carefully analyzed,in order to fully understand the foundations of these processes.     

Determination of copper, manganese and zinc in human liver

Autopsied liver tissue samples collected from 42 males and 31 females were analyzed for copper, manganese and zinc using atomic absorption spectrometry (AAS). With the exception of two liver samples for which the copper levels were determined to be 74.8 and 104.0 g/g (dry weight), hepatic copper concentrations were found to range from 1.7 to 32.4 g/g with a mean concentration of 14.2 g/g and standard deviation of 7.0 g/g. Manganese concentrations (with the exception of one sample having 12.9 g/g) ranged from 0.22 to 4.6 g/g with a mean of 2.26 ± 1.00 g/g. Hepatic zinc levels averaged 118.3 ± 44.4 g/g and ranged from 38.5 to 231.3 g/g. There were no apparent trends for the levels of any metals versus age nor were there any differences in average hepatic metal concentrations for males and females. © Rapid Science 1998.     

The contribution of size-fractionated plankton to biomass and primary production of phytoplankton in saline–alkaline ponds

Primary productivity, biomass and chlorophyll-a of size fractionated phytoplankton (<0.22 m, <3 m, <8 m, <10 m, <40 m, <64 m, <112 m and <200 m) were estimated in 6 ponds and 5 experimental enclosures. The results showed that the planktonic algae less than 10 m are important in the biomass and production of phytoplankton in saline–alkaline ponds. The production of size fractionated phytoplankton corresponding to <112 m, <10 m and <3 m in saline–alkaline ponds were 10.5 ± 6.6 , 8.6 ± 5.4 and 0.33 ± 0.1 mgC l^–1 d^–1, respectively. Mean community respiration rate was 1.80 ± 0.73, 1.69 ± 0.90 and 1.38 ± 1.12 mgC l^–1 d^–1, respectively. The average production of phytoplankton corresponding to micro- (10–112 m), nano- (3–10 m) and pico- (<3 m) were 1.61, 8.30 and 0.33 mgC l^–1 d^–1, respectively. The ratio of those to the total phytoplankton production was 15%, 79% and 3%, respectively. The mean respiration rate of the different size groups was 0.11, 0.31 and 1.38 mgC l^–1 d^–1; the ratio of those to total respiration of phytoplankton was 6%, 17% and 77%, respectively. The production of size-fractionated phytoplankton corresponding to <200 m, <10 m and <3 m in enclosures was 2.19 ± 1.63, 2.08 ± 1.75 and 0.22 ± 0.08 mgC l^–1 d^-1, respectively. Mean community respiration rates were 1.25 ± 1.55, 1.17 ± 1.42 and 0.47 ± 0.32 mgC l^–1 d^–1, respectively. The average production of phytoplankton corresponding to micro- (10–200 m), nano- (3–10 m) and pico- (<3 m) plankton was 0.11, 1.86 and 0.22 mgC l^–1 d^–1, respectively. The ratio of those to the total production of phytoplankton was 5%, 85% and 10%, respectively. The mean respiration rate of different size groups were 0.08, 0.72 and 0.46 mgC l^–1 d^–1, the ratio of those to total respiration of phytoplankton was 6%, 57% and 37%, respectively. The concentrations of chlorophyll-a of the phytoplankton in the corresponding size of micro- (10–112 m), nano- (3–10 m) and pico- (<3 m) plankton in the experimental ponds were 19.3, 98.2 and 11. 9 g l^–1, respectively. The ratio of those to the total chlorophyll-a was 15%, 76% and 9%, respectively. The concentrations of chlorophyll-a of phytoplankton micro- (10–200 m), nano- (3–10 m) and pico- (<3 m) plankton in enclosures were 1.7, 34.3 and 3.0 g l^–1, respectively. The ratio of those to the total chlorophyll-a was 4%, 88% and 8%, respectively.     

Aluminum-induced secretion of both citrate and malate in rye

Aluminum (Al)-resistant mechanisms responsible for Al-induced secretion of organic acids are poorly understood. In this study, we characterized the Al-induced secretion of both citrate and malate from rye (Secale cereale L. cv. King). Secretion of organic acids increased with increasing concentration (10, 30 and 50 M) and duration of Al treatments. Neither phosphorous (P) deficiency up to 15 days nor addition of 50M lanthanum, 50 M lead, 10 M cadmium, or 200 M manganese caused secretion of organic acids, suggesting that this secretion was a specific response to Al stress. Aluminum activated citrate synthase, the main enzyme for the synthesis of citrate, but its activation occurred only in the root tip. The elongation of roots of an Al-sensitive cultivar of wheat (Tritium aestivum L. cv. Scout 66) was not inhibited by 50 M Al in the presence of externally applied 50 M citrate or 400 M malate. The secretion of citrate and malate from intact rye roots exposed to 50 M Al corresponded to 31.3 ± 1.7 M and 11.5 ± 2.5 M, respectively, in the rhizosphere based on an assumption of a 2 mm thick unstirred layer around root tips. This result indicated that Al-resistance in rye was achieved by the Al-induced synthesis of citrate in root apices followed by Al-induced specific secretion of citrate from root tips.     

Clozapine and Several Other Antipsychotic/Antidepressant Drugs Preferentially Block the Same ‘Core’ Fraction of GABAA Receptors

Clozapine and several other antipsychotic/antidepressant drugs that fully or partially block GABA_A receptors were tested at concentrations that reversed the inhibitory effect of 1 M GABA on ³⁵S-t-butylbicyclophosphorothionate ([³⁵S]TBPS) binding to rat forebrain membranes only about 20–30%, here designated core fractions. Clozapine at 10 M reverses 1 M GABA 25 ± 4.0% (n = 23) (its core fraction). Fourty three compounds were tested alone, and pairwise together with 10 M Clozapine. The core fractions of some of the compounds yielded significant additive reversals together with 10 M Clozapine, while others did not. A group of 14 compounds of which 7 are clinically effective antipsychotic drugs, including Chlorprothixene, Clomacran, Clopipazan, Fluotracen, Sulforidazine, Thioproperazine, and cis-Thiothixene, were statistically non-additive with 10 M Clozapine, suggesting that all of these drugs selectively block the same core population of GABA_A receptors as Clozapine. These non-additivities also suggest that Clozapine at 10 M fully saturates a subset of GABA_A receptors blocked by 1 M GABA. Therefore, Clozapine probably blocks 2 or more types of GABA_A receptors, but only half of the receptors that are sensitive to 1 M GABA. A second group of 12 compounds of which 6 are clinically active antidepressant/antipsychotic drugs including Amoxapine, Clothiapine, Dibenzepine, Inkasan (Metralindole), Metiapine and Zimelidine were slightly, but significantly, additive with Clozapine suggesting that these compounds block most of Clozapine's core fraction, plus a small additional fraction. A third group consisted of ten compounds that yielded larger (R > 80) and statistically highly significant additivities with Clozapine. Complete additivity was obtained with Bathophenanthroline disulfonate, and Isocarboxazid, suggesting that they block GABA_A receptors other than those blocked by 10 M Clozapine. Seven classical GABA_A receptor blockers, also tested at concentrations yielding 21 to 33% reversal alone, were all significantly additive with 10 M Clozapine, but in no case was the additivity complete. The largest additivity was obtained with Pitrazepine (21%) and the smallest with Tubocurarine (9%). These results provide further support for the notion that selective blockade of the same subset of GABA_A receptors may contribute to the clinical antipsychotic/antidepressant effects of Clozapine. The B_opt values for Clozapine are 50 ± 1.7% and 26 ± 2.6% ( n = 3) in whole rat forebrain and cerebellum, respectively, confirming that clozapine-sensitive GABA_A receptors are unevenly distributed in the brain. The sedative and anxiolytic properties of Clozapine and other antipsychotic drugs may be due to selective blockade of GABergic disinhibition at certain interneurons.     

Mercury contamination in Lake Xolotlán (Managua)

Total mercury was measured in different compartments of Lake Xolotlán's (Managua) ecosystemviz., sediments, water, fish and men. Sediments from 18 localities at 5 depths inside the sediment (5, 10, 15, 20 and 25 cm) contained an average concentration of 0.62 g Hg.g^–1±0.46 at the surface, with extreme values of 0.16 and 1.8 g.g^–1. The highest concentration was observed at 25 cm depth in front of the chlor-alkaly factory (ELPESA). This maximum is associated with the period of highest production of this factory. The highest mercury concentrations in water were also measured close to the discharge of ELPESA,viz. 787 g.Hg^–1 in January and 506 g.g^–1 in April. The mean mercury concentrations measured in the muscles of the most consumed fish were 0.63 g.g^–1±0.22 (extreme values 0.22 and 1.45) inCichlasoma managuense, and 0.07 g.g^–1±0.14 (extreme values 0.004 and 0.63) inC. citrinellum. The concentration in the liver was 0.79 g.g^–1±1.29 inC. managuense and 0.62 g.g^–1±0.44 inC. citrinellum. Human hairs (n=98) of fishermen and their families contained 5.03 g.g^–1±6.2 (extreme values 0.02 and 38.22). The mean concentration measured in men was 6.22 g.g^–1±6.34 (n=58), and in women 3.39 g.g^–1±5.7 (n=40). The average mercury concentration of hairs of workers of ELPESA was 91.24 g.g^–1±156.9 (extreme values 0.46 and 724.53; n=32). We conclude that total mercury levels in the various ecosystem compartments are very high and mercury contamination in the lake may be considered as dangerous for human health.     

Pre-epithelial mucus layer in the colon of conventional and germ-free rats

Summary The pre-epithelial mucus layer (PML) and epithelial mucins were studied by mucin histochemistry in 10m-thick celloidinstabilized cryostat sections in the proximal and distal colon of conventional and germ-free rats aged 120 and 350 days. No continuous PML was found in the proximal colon. A continuous mucus blanket, of fairly homogenous thickness, was observed in the distal colon, where the PML-thickness was 40±24 m at 120 days of age and 44±22 at 350 days of age in conventional rats, and 25±17m (120 days) and 22±10 (350 days) in germ-free rats. The stainability of the PML by periodic acid-Schiff and Alcian Blue at pH 2.5 and 1.0 was stronger in conventional rats than in germ-free rats, indicating higher concentrations of mucosubstances and of acid and sulphated mucins, respectively. The PML of the conventional rat distal colon showed a stratified structure of up to eight sublayers. In the distal colon of germ-free rats, the whole gut wall thickness was reduced 47% compared to the conventional rat (germ-free: 185±73m, conventional: 350±115m). No stratification of the PML was observed. The presence of intestinal microflora obviously had a strong influence on the thickness, compactness, mucin content, mucin composition and structure of the pre-epithelial mucus layer.     

TBARS,carnitine, and reduced glutathione levels in human bladder carcinoma

In this study, we investigated tissue levels of reduced glutathione (GSH) and carnitine as well as thiobarbituric acid reactive substances (TBARS, as a marker of lipid peroxidation) levels in bladder carcinoma and control group of patients. The average GSH, carnitine and TBARS levels for tumor group were respectively 7.11 ± 3.3 g/mg protein, 1.81 ± 0.39 nmol/mg protein, and 4.29 ± 3.2 mol/mg protein, versus 14.45 ± 4.11 g/mg protein, 2.14 ± 0.66 nmol/mg protein, and 2.3 ± 0.6 mol/mg protein for normal bladder tissues. Thus, tissue reduced glutathione levels (GSH) were significantly lower in patients as compared with the control group (p < 0.001) whereas average TBARS levels in the tumor group were found to be higher than those in control group. The average tissue carnitine levels in the patient group were found to be lower compared with the control group but the difference was not statistically significant (p > 0.05).     

Method of isolation of cysteine constitutive mutants of the cysteine regulon in Salmonella typhimurium.

Summary Size and shape of mitochondrial DNA molecules of Schizosaccharomyces pombe were analyzed by electron microscopy. Besides numerous linear molecules, circular molecules ranging from 0.83 m to 12.81 m were found. Depending on the method of preparation, both closed and open circular molecules were found. Most of the circular molecules could be assigned to five major size classes of 0.83±0.05 m, 1.7±0.05 m, 4.74±0.04 m, 5.74±0.04 m, and 8.32±0.07 m. Possible explanations for the different size classes of mitochondrial DNA molecules are discussed.     

Coccidia of Brazilian edentates: Eimeria cyclopei n.sp. from the silky anteater,Cyclopes didactylus (Linn.) and Eimeria choloepi n.sp. from the two-toed sloth,Choloepus didactylus (Linn.)

Summary Eimeria cyclopei n.sp. is described from the silky anteater, Cyclopes didactylus, from Pará State, north Brazil. Undifferentiated oocysts, passed in the faeces, complete sporulation in seven days at 26 to 28°C. Oocysts are ellipsoidal to sub-spherical, with a mean size of 28.1 × 23.6 m: the wall is 1.5 to 2.0 m thick, apparently with an outer thin, colourless membrane and two inner, thicker, striated and yellowish layers. There is no micropyle, oocyst residuum or polar body. The mean measurements of sporocysts are 19.0 × 9.0 m, and they are slightly asymmetrical, elongate pear-shape, with a plug-shaped Steida body projecting beyond the end of the sporocyst. Sporozoites are as long as or longer than the sporocysts: The sporocyst residuum is scattered between sporozoites in younger specimens and becomes condensed into rounded mass in older ones. The endogenous stages occur in the epithelial cells of the ileum, on the lumenal side of the host-cell nucleus. Uninucleate meront, microgamont and macrogamont precursors are recognizable morphologically. Mature meronts are 20.0 × 15.7 m some produce 12 to 20 merozoites which are 8.7 × 2.0 m, and others 10 to 26 merozoites which are 11.4 × 2.0 to 15.0 × 3.0 m. Mature microgamonts which are 27.5 × 24.1 m, produce from 150 to 170 microgametes of 7.1 × 1.0 m: microgametes have two flagella of unequal length. Mature macrogamonts are 28.4 × 24.5 m Eimeria choloepi n.sp. is recorded from the two-toed sloth, Choloepus didactylus, from the same area of Brazil. Undifferentiated oocysts, passed in the faeces, complete sporulation in 23 days at 26 to 28°C. Oocysts with a mean size of 23.0 × 20.3 m, have a wall 2.0 to 2.5 m thick which is composed of two thick, yellowish and striated outer layers and a delicate, colourless inner one. There is no micropyle, oocyst residuum or polar granule. Mature sporocysts with a mean size of 11.3 × 7.1 m, are ellipsoidal to egg-shaped and have a poorly developed Steida body. The sporocyst residuum is composed of a small number of large globules: The sporozoites are longer than the sporocyst and strongly recurved. The endogenous stages occur in epithelial cells of the ileum, on the lumenal side of the host-cell nucleus. Dimorphic meronts produce 8 to 18 merozoites which are either 13.0 × 2.0 m or 13.0 × 3.0 m. Microgamonts produce 50 to 80 microgametes of 8.0 × 1.0 m. Mature macrogamonts are 18.3 × 17.9 m. ac]19820212     

Inward rectifier K channels in renal epithelioid cells (MDCK) activated by serotonin

Summary The present study has been performed to test for the effect of intracellular calcium and of serotonin on the channel activity in patches from subconfluent MDCK-cells. In inside-out patches, inwardly rectifying potassium-selective channels are observed with open probabilities of 0.01±0.01, 0.24±0.03 and 0.39±0.07, at 100 nmol/liter, 1 mol/liter or 10 mol/liter calcium activity, respectively. The single-channel slope conductance is 34±2 pS, if the potential difference across the patch (V ) is zero, and approaches 59±1 pS, ifV is –50 mV, cell negative. In the cell-attached mode, little channel activity is observed prior to application of serotonin (open probability=0.03±0.03). If 1 mol/liter serotonin is added to the bath perfusate, the open probability increases rapidly to a peak value of 0.34±0.04 within 8 sec. In continued presence of the hormone, the open probability declines to approach 0.06±0.02 within 30 sec. At zero potential difference between pipette and reference in the bath (i.e., the potential difference across the patch is equal to the potential difference across the cell membrane), the single-channel conductance is 59±4 pS. In conclusion, inwardly rectifying potassium channels have been identified in the cell membrane of subconfluent MDCK-cells, which are activated to a similar extent by increase of intracellular calcium activity to 1 mol/liter and by extracellular application of 1 mol/liter serotonin.     

Mercury budget of an upland-peatland watershed

Inputs, outputs, and pool sizes oftotal mercury (Hg) were measured in a forested 10 hawatershed consisting of a 7 ha hardwood-dominatedupland surrounding a 3 ha conifer-dominatedpeatland. Hydrologic inputs via throughfall andstemflow, 13±0.4 g m^–2 yr^–1over the entire watershed, were about doubleprecipitation inputs in the open and weresignificantly higher in the peatland than in theupland (19.6 vs. 9.8 g m^–2 yr^–1). Inputs of Hg via litterfall were 12.3±0.7g m^–2 yr^–1, not different in thepeatland and upland (11.7 vs. 12.5 g m^–2yr^–1). Hydrologic outputs via streamflow were2.8±0.3 g m^–2 yr^–1 and thecontribution from the peatland was higher despiteits smaller area. The sum of Hg inputs were lessthan that in the overstory trees, 33±3 gm^–2 above-ground, and much less than eitherthat in the upland soil, 5250±520 gm^–2, or in the peat, 3900±100 gm^–2 in the upper 50 cm. The annual flux of Hgmeasured in streamflow and the calculated annualaccumulation in the peatland are consistent withvalues reported by others. A sink for Hg of about20 g m^–2 yr^–1 apparently exists inthe upland, and could be due to either or bothstorage in the soil or volatilization.     

In vitro micropropagation of Piper longum – an important medicinal plant

Efficient and rapid tissue culture systems were developed for Piper longum, an important medicinal plant, through shoot tip multiplication and direct regeneration. Multiple shoots were induced from shoot tips cultured on agar-based Murashige and Skoog (MS) medium containing 4.44–22.19 M benzyladenine (BA) and 4.64–13.9 M kinetin (K). Maximum number of shoots were induced with 8.9 M BA and 4.64 M K. Adventitious shoot regeneration from leaf segments was achieved on MS containing 3.6–22.19 M BA along with 3.31–12.4 M picloram (P). Shoot differentiation occurred directly from the leaf bases without intermediale callus formation. Maximum shoot buds were obtained on MS medium with 17.76 M BA and 8.28 M P. Elongated shoots were separated and rooted in MS supplemented with 2.46 M indole butyric acid (IBA). Plantlets, thus developed were established in soil.     

Somatic embryogenesis in callus cultures of Rosa hybrida L. cv. Landora

Callus was initiated from immature leaf and stem segments of rose (Rosa hybrida cv. Landora) and subcultured every four weeks on a basal medium of half-strength Murashige & Skoog (1962) salts plus 30 g l^-1 sucrose (1/2 MS) and supplemented with 2.2 M BA, 5.4 M NAA and 2.2–9.0 M 2,4-D. Embryogenic callus and subsequently somatic embryos were obtained from 8-week-old callus culture on 1/2 MS+2.2 M BA+0.05 M NAA+0.3 M GA₃+200–800 mg l^-1 L-proline. Long-term cultures were established and maintained for up to 16 months by repeated subculture of embryogenic callus on L-proline deficient medium. About 12% of cotyledonary stage embryos taken from cultures cold-stored at 8±1°C for 4 days germinated on 1/2 MS+2.2 M BA+0.3 M GA₃+24.7 M adenine sulphate.Abbreviations BA benzyladenine - NAA -naphthaleneacetic acid - 2,4-D 2,4-dichlorophenoxyacetic acid - GA₃ gibberellic acid     

Uptake of sewage derived nitrogen by<Emphasis Type="Italic"> Ulva rigida</Emphasis> (Chlorophyceae) in Bahía Nueva (Golfo Nuevo,Patagonia, Argentine)

Uptake kinetics of nitrogen derived from sewage–seawater mixtures (2.5–20% v/v effluent) were determined in the laboratory for Ulva rigida (Chlorophyceae) native from Bahía Nueva (Golfo Nuevo, Patagonia, Argentine). In terms of nitrogen concentration, experimental enrichment levels varied between 53.7 and 362.3M of ammonium and between 0.77 and 6.21M of nitrate+nitrite. Uptake rates were fitted to the Michaelis–Menten equation, with the following kinetic parameters: ammonium: V_max = 591.2molg^–1h^–1, K _s=262.3M, nitrate+nitrite: V _max=12.9molg^–1h^–1, K _s=3.5M). Both nutrients were taken up simultaneously, but ammonium incorporation was faster in all cases. The results show a high capability of Ulva rigida to remove sewage-derived nitrogen from culture media. In the field, most of the nitrogen provided by the effluent would be tied up in algal biomass, supporting low nitrogen levels found at a short distance away from the source.     

In vitro comparison of ceftazidime,aztreonam, cefpirome,gentamicin, imipenem,enoxacin, and ticarcillin plus clavulanic acid against 108 strains ofPseudomonas maltophilia

Pseudomonas maltophilia is an uncommon cause of hospital-acquired infection and is resistant to most of the antimicrobial agents used in the treatment of gram-negative infections. Susceptibility of 108 isolates ofP. maltophilia to ceftazidime, aztreonam, defpirome, gentamicin, imipenem, enoxacin, and ticarcillin plus clavulanic acid was determined by an agar dilution method. The isolates were in general resistant to the antibiotics. Imipenem and cefpirome were not active at clinically achievable levels. Of the isolates, 20% were susceptible to 16 g/ml ceftazidime, 53% were susceptible to 4 g/ml enoxacin, 10% were susceptible to 4 g/ml gentamicin, and 25% were susceptible to 64 g/ml ticarcillin plus 2 g/ml clavulanic acid.     

Pesticides and heavy metals in Danish streambed sediment

The role of streambed sediment as a sink for pesticides and heavy metals was investigated in 30 Danish lowland streams. The investigated streams drain catchments varying in hydrology, topography, soil type and land use. The <250 m newly accumulated fraction of the uppermost 1–2 cm layer of streambed sediment was analysed for 19 old and modern pesticides and 9 heavy metals. DDE was present in the sediment of all the streams. Of the herbicides, fungicides and insecticides currently in use, the most frequently detected was diuron (50.0%), fenpropimorph (66.7%) and lambda-cyhalothrin (6.7%), respectively. The pesticides detected in the highest concentration were fenpropimorph (1700 ng g^–1), propiconazole (130 ng g^–1) and isoproturon (110 ng g^–1). The heavy metals are listed in order of increasing median concentration: Cd (0.80 g g^–1), Co (9.1 g g^–1), As (12.0 g g^–1), Ni (19.0 g g^–1), Cr (19.2 g g^–1), Pb (19.7 g g^–1), Cu (20.1 g g^–1), V (28.5 g g^–1), Zn (103 g g^–1). The average number of pesticides detected in the 27 streams draining predominantly agricultural catchments was (3.7±2.0) being higher (p=0.077) than in the three streams draining non-agricultural catchments (1.7±0.6). Pesticides were significantly related to catchment size, soil type and hydrological regime. Several heavy metals (Cr, Cu, Pb, V and Zn) were related to urban activity and soil type.     

Plant development in long-term embryogenic callus lines of Cucurbita pepo

Embryogenic callus derived from pumpkin hypocotyl segments was induced and maintained for 15 years on MS medium supplemented with the auxins IBA (4.9 M), 2, 4-D (4.5 M) or IAA (5.7 M). On induction media continued embryo maturation and development of adult plants typically failed. Therefore, small embryogenic clumps and individually isolated embryos were subcultured two to four times on one of the conversion media: MS supplemented with 1.5% sucrose and (a) no hormone, (b) 2.9 M IAA, (c) 5.7 M IAA, (d) 11.4 M IAA, (e) 12 M IEt, (f) 3.8 M ABA or (g) 2% activated charcoal. The cell line and the kind of auxin used in the induction and maintenance medium, both had a marked influence on the development of plantlets. The best result was achieved with a line that has been induced and maintained for 15 years on MS with IBA. In the IBA line, out of 100 embryos, 77 developed into plantlets on MS medium supplemented with 11.4 M IAA.Abbreviations IAA indole-3-acetic acid - IBA indole-3-butyric acid - BA 6-benzylaminopurine - ABA abscisic acid - 2, 4-D 2, 4-di-chlorophenoxyacetic acid - IEt indole-3-etha-nol - MS Murashige and Skoog (1962) medium     

Ecotoxicity of lead to the zebra musselDreissena Polymorpha,Pallas

The effect of lead on the filtration rate of the zebra musselDreissena polymorpha was investigated, together with the accumulation of Pb in the soft tissues of the mussels. The NOEC-filtration was 116 g.l^–1 (0,56 mol.l^–1) and the EC₅₀-filtration was 370 g.l^–1 (1.79 mol.l^–1). The NOEC-accumulation was the concentration found in the control water (1.4g.l^–1). These experiments show that the EC₅₀-filtration for Pb is similar to that for Cd, higher than that for Cu and lower than that for Zn. The water quality criteria for lead allow 25 g Pb.l^–1 in surface water. This will not cause short-term effects. Long-term effects may, however, occur, since an accumulation of Pb as low as 16 g.l^–1 was recorded in this study.