首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 46 毫秒
1.
To assess the influence of water temperature on silver uptake, rainbow trout Oncorhynchus mykiss ( c . 50 g; held at 13° C) were exposed to 0·1 μM AgNO3 in ion‐poor water for 1 week at 4 and 16° C without previous temperature acclimation. To assess the influence of temperature on elimination of previously accumulated Ag, rainbow trout were exposed to 0·1 μM AgNO3 in ion‐poor water for 1 week at 12° C, then were randomly divided amongst two Ag‐free water containers, differing only in temperature (3 and 16° C), for 2 months. In the uptake study greater accumulation of Ag was seen in the gills, plasma and especially the livers and bile of 'warm' rainbow trout (16° C) compared to 'cold' rainbow trout (4° C), which can be explained by the higher metabolic rates of the warmer fish. In the depuration study there was no net elimination of Ag from the livers and bile but there was biphasic elimination of Ag from the gills and plasma of 'warm' and 'cold' fish, but with few differences between them. This indicated that temperature‐dependent processes were less important in Ag elimination than in Ag uptake. Toxicokinetic modelling of Ag uptake by livers indicated four‐fold greater uptake of Ag by 'warm' rainbow trout compared to 'cold' rainbow trout (one compartment uptake model). Elimination of previously accumulated Ag from the plasma was best fitted by a two compartment rate‐constant based model, with approximately half the plasma Ag load eliminated within 24 h, followed by slower elimination of Ag over 2 months.  相似文献   

2.
Role of ethylene in de novo shoot morphogenesis from explants and plant growth of mustard ( Brassica juncea cv. India Mustard) in vitro was investigated, by culturing explants or plants in the presence of the ethylene inhibitors aminoethoxyvinylglycine (AVG) and AgNO3. The presence of 20 μ M AgNO3 or 5 μ M AVG in culture medium containing 5 μ M naphthaleneacetic acid and 10 μ M benzyladenine were equally effective in promoting shoot regeneration from leaf disc and petiole explants. However, AgNO3 greatly enhanced ethylene production which reached a maximum after 14 days, whereas ethylene levels in the presence of AVG remained low during 3 weeks of culture. The promotive effect of AVG on shoot regeneration was overcome by exogenous application of 25 μ M 2-chloroethylphosphonic acid (CEPA), but AgNO3-induced regeneration was less affected by CEPA. For whole plant culture, AVG did not affect plant growth, although it decreased ethylene production by 80% and both endogenous levels of 1-aminocyclopropane-1-carboxylate (ACC) synthase and ACC by 70–80%. In contrast, AgNO3 stimulated all 3 parameters of ethylene synthesis. Both AgNO3 and CEPA were inhibitory to plant growth, with more severe inhibition occuring in AgNO3. Leaf discs derived from plants grown with AVG or AgNO3 were highly regenerative on shoot regeneration medium without ethylene inhibitor, but the presence of AgNO3 in the medium was inhibitory to regeneration of those derived from plants grown with AgNO3.  相似文献   

3.
In vitro cultures and endogenous abscisic acid (ABA) analyses with gas chromatography-selected ion monitoring-mass spectrometry (GC-SIM-MS) were used to study the effects of AgNO3 and polyethylene glycol (PEG) on white spruce ( Picea glauca ) somatic embryo maturation and endogenous ABA contents, Normally, in the absence of ABA, white spruce somatic embryos cannot mature. However, AgNO3 and PEG stimulated somatic embryo maturation by increasing the number of cotyledonary embryos. A combination of 100 μ M AgNO3 and 40 g l−1 PEG was the treatment that was most effective in enhancing cotyledonary embryo formation without exogenous ABA. Either AgNO3 or PEG was able to increase endogenous ABA levels of the embryogenic culture but a combination of AgNO3 and PEG was the most effective treatment. Stimulation of cotyledonary embryo formation by AgNO3 occurred only at low ABA levels, while PEG promoted embryo formation at all exogenous ABA concentrations. Germination tests indicated that AgNO3 had no negative effects on embryo germination and conversion while the PEG-treated embryos failed to germinate.  相似文献   

4.
The 96-h LC50 on brown trout Salmo trutta of a commercial iron (III) sulphate liquor, used for treating reservoirs to reduce algal growth, was 28 mg total Fe l−1 (0·05 mg soluble Fe l−1). The 96-h LC50 for analar grade iron (III) sulphate was 47 mg total Fe l−1 (0·24 mg soluble Fe l−1). Lethal and sublethal exposure to both grades of iron resulted in accumulation on the gill, which appears to be the main target for iron toxicity. Greater iron accumulation occurred during exposure to commercial iron sulphate liquor. Physical clogging of gills and gill damage was seen during lethal and sublethal exposure to iron. Gill tissue analysis showed no evidence of iron uptake into gill tissues during lethal or sublethal exposure to iron. Iron did not accumulate in plasma of fish exposed to iron compared to controls. Respiratory disruption due to physical clogging of the gills is suggested as a possible mechanism for iron toxicity.  相似文献   

5.
Some physiological parameters were measured in adult rainbow trout during a 10-day exposure to 180 μg Altotal l−1 in acid water (pH 4.7) with or without humic substances (10 mg l). The fish were acclimatized to pH 5.0 for 7 days prior to the experimental treatments.
Chemical analyses revealed that, in the presence of human substances, 74–80% of the A1 was organic bound, while in the absence of humic substances most of the Al(987percnt;) occurred in the inorganic form.
Al bound to humic substances (13–150 μg l−1) did not alter the plasma NaCl-concentration, nor the haematocrit value, of rainbow trout during an exposure period of 10 days. This contrasts with the high death rate obtained within 2–3 days when most of the A1 (175 μg l−1) was in the inorganic form. The lethality was accompanied by a 25% decrease in the plasmaconcentration of NaCl and a doubling of the haematocrit value. Bulk analysis revealed that when the metal was present in inorganic forms the total Al content of the gills (75 μg A1 g−1 wet weight) was 15 times higher than when it was present as bound to the humic substances. These experiments showed that the accumulation of A1 at the gills was accompanied by physiological disturbances, both being a function of the chemical speciation of Al.  相似文献   

6.
Aim:  To investigate the effects of feeding and induction strategies on the production of Bm R1 recombinant antigen.
Methods and Results:  Fed-batch fermentation was studied with respect to the specific growth rate and mode of induction to assess the growth potential of the bacteria in a bioreactor and to produce high yield of Bm R1 recombinant antigen. Cells were grown at a controlled specific growth rate (μset) during pre-induction, followed by constant feeding postinduction. The highest biomass (24·3 g l−1) was obtained during fed-batch process operated at μset of 0·15 h−1, whereby lower μset (0·075 h−1) gave the highest protein production (9·82 mg l−1). The yield of Bm R1 was increased by 1·2-fold upon induction with 1 mmol l−1 IPTG (isopropyl-β- d -thiogalactoside) compared to using 5 mmol l−1 and showed a further 3·5-fold increase when the culture was induced twice at the late log phase.
Conclusions:  Combination of feeding at a lower μset and twice induction with 1 mmol l−1 IPTG yielded the best result of all variables tested, promising an improved method for Bm R1 production .
Significance and Impact of the Study:  This method can be used to increase the production scale of the Bm R1 recombinant antigen to meet the increasing demand for Brugia Rapid, a commercial diagnostic test for detection of brugian filariasis.  相似文献   

7.
Embryos of Danio rerio are highly susceptible to extracts of the plants Tephrosia vogelii and Asystasia vogeliana . The concentration of the dried extracts at which 50% of the embryos were affected (EC50) after 24 h exposure were 320 and 572 μg l−1, respectively; corresponding 50% mortality (LC50) values after 48 h exposure were 493 and 869 μg l−1. Results indicate that the use of these ichthyotoxic plants might have a severe impact on the survival of fish larvae in the field.  相似文献   

8.
Long-term ammonia exposure of turbot: effects on plasma parameters   总被引:2,自引:0,他引:2  
Turbot juveniles were exposed to four ammonia concentrations [0·17 (L), 0·34 (M), 0·73 (MH) and 0·88 (H) mg l−1 NH3-N] for different exposure durations (28 days minimum to 84 days). Their physiological status and growth performances were compared to a control group [0·004 (C) mg l−1 NH3-N]. No growth was observed in the H group, and by day 57, mass increase in the MH group was only 15% of that in group C. During the first month growth in the L group was similar to that in control group while it was lower (33%) in the M group; afterwards the L and M groups had a similar growth (half that of controls). Accumulation of total ammonia nitrogen (TA-N) in plasma was dependent on ambient ammonia concentrations. Plasma urea levels in ammonia-exposed fish were lower, similar or greater than in controls (depending on ammonia concentration or exposure duration). Osmolarity, Cl and Na+ plasma concentrations were stable in the L and M groups. The increases in Na+, Cl, K+ and total Ca concentrations observed by the end of the experiment in the H and MH groups suggest that fish failed to adapt. There was an initial rise in plasma cortisol in all ammonia-exposed groups followed by a return to basal level (1·7–4 ng ml−1) in the L and M groups. In group MH, plasma cortisol peaked at 42 ng ml−1 by day 14, and after a decline at c . 1 month (14 ng ml−1), it rose again.  相似文献   

9.
Xylanolytic activity of commercial juice-processing enzyme preparations   总被引:2,自引:0,他引:2  
Of 22 commercial juice-processing enzyme preparations investigated, Clarex ML was found to exhibit the highest xylanase activity. The xylanase from Clarex ML was most active at 50–60°C and pH 5·0–5·5. The K m and V max values of the enzyme with oat-spelt xylan as the substrate were 8·6 mg ml−1 and 42 μmol xylose l−1 min−1, respectively. Xylobiose was the main product of enzymatic hydrolysis of xylan.  相似文献   

10.
Abstract The populations of chemolithoautotrophic (colorless) sulfur bacteria and anoxygenic phototrophic bacteria were enumerated in a marine microbial mat. The highest population densities were found in the 0–5 mm layer of the mat: 2.0 × 109 cells cm−3 sediment, and 4.0 × 107 cells cm−3 sediment for the colorless sulfur bacteria and phototrophs, respectively. Kinetic parameters for thiosulfate-limited growth were assessed for Thiobacillus thioparus T5 and Thiocapsa roseopersicina M1, both isolated from microbial mats. For Thiobacillus T5, growing at a constant oxygen concentration of 43 μmol l−1, μmax was 0.336 h−1 and K s 0.8 μmol l−1. Phototrophically grown Thiocapsa strain M1 displayed a μmax of 0.080 h−1 and a K s of 8 μmol l−1 when anoxically grown under thiosulfate limitation. In a competition experiment with thiosulfate as electron donor, Thiocapsa became dominant during a 10-h oxic/14-h anoxic regimen at continuous illumination, despite the higher affinity for thiosulfate of Thiobacillus .  相似文献   

11.
Of various commercial enzyme preparations examined, Cytolase M102 was found to contain the highest glucosyltransferase activity (55 U ml−1). It rapidly converted maltose to panose (Glcα1 → 6Glcα1 → 4Glc) with a V max value of 5·8 mmol l−1 min−1 at 50°C in 0·05 mol l−1 sodium acetate buffer (pH 4·4). The K m value of the enzyme for maltose was 750 mmol l−1. Yields of panose and glucose after 45 min of reaction, for example, were 47·2% and 52·8%, respectively, on the basis of the amount of maltose consumed.  相似文献   

12.
Histidine decarboxylase (HDC) was purified to homogeneity from Leuconostoc ' nos 9204, a wine lactic acid bacterium. Histidine decarboxylase comprised two subunits, respectively α and β. The hdc gene was cloned and sequenced. The gene encodes a single polypeptide of 315 amino acids, demonstrating that Leuc. ' nos 9204 HDC was synthesized as a precursor proHDC π6 (Mr 205 000). A cleavage between Ser-81 and Ser-82 generated the α (Mr 25 380) and β (Mr 8840) chains, which suggested that the holoenzyme exists as a hexameric structure (αβ)6. At the optimal pH of 4·8, the HDC activity exhibited a simple Michaelis-Menten kinetic ( K m = 0·33 mmol l−1, V max = 17·8 μmol CO2 min−1 mg−1), while at pH 7·6 it was sigmoidal (cooperativity index of 2). Histamine acted as a competitive inhibitor ( K i = 32 mmol l−1). The similarities of these results with those described for other bacterial HDC support the assumption that the pyruvoyl enzymes evolved from a common ancestral protein and have similar catalytic mechanisms. These results also confirmed that the main lactic acid bacterial species responsible for malolactic fermentation in red wine is able to produce histamine. Bacteria carrying the HDC activity must be avoided during selection of strains for the production of malolactic starters.  相似文献   

13.
Preference responses of zebrafish to 10−3, 10−4 and 10−5M alanine (Ala) were concentration- dependent. Behavioural responses to copper (Cu) and Cu + Ala mixtures were also assessed. Zebrafish avoided 100 and 10 μg Cu l−1, but not 1 μg l−1. Mixtures of 10−3 m Ala+ 100 μg Cu l−1 and 10 4 M Ala + 10 μg Cu 1−1 were avoided as intensely as was Cu alone. Responses to 10−3 M Ala + 10 or 1 μg Cu l−1 and 10 4 M Ala +1 μg Cu l−1 did not differ statistically from controls (no detectable preference or avoidance). These results demonstrate, firstly, that a concentration of a pollutant avoided by itself (10 μg Cu l−1) may not be avoided when encountered with an attractant chemical stimulus (Ala) and may suppress the preference for an attractant stimulus, and secondly, that a concentration of a pollutant not avoided by itself and not considered deleterious (1 μg Cu l−1) suppresses attraction to Ala (an important constituent of prey odours for many fishes).  相似文献   

14.
Note: Purification of amylase secreted from Bifidobacterium adolescentis   总被引:1,自引:0,他引:1  
Bifidobacterium adolescentis Int-57 isolated from human faeces produced extracellular amylase. The enzyme was purified from the culture supernatant fluids by ammonium sulphate precipitation, gel-filtration chromatography (Sephadex-G-75), ion-exchange chromatography (CM-cellulose) and FPLC. SDS-PAGE of the purified enzyme revealed a major band with an apparent molecular weight of 66 kDa. The pI was 5·2. Enzyme activity was optimal at 50°C, and at pH 5·5. The enzyme was stable at 20–40°C, and at pH 5–6 with a K m value of 2·4 g l−1 soluble starch. The activation energy was 42·3 kJ mol−1. The enzyme was significantly inhibited by maltose (10%), glucose (10%), Cu2+ (5 mmol l−1), Zn2+ (5 mmol l−1), N- bromosuccinimide (5 mmol l−1), EDTA (5 mmol l−1), I2 (1 mmol l−1) and activated by β-mercaptoethanol (10 mmol l−1).  相似文献   

15.
The effects of sublethal waterborne Zn (2·28 μmol l−1) on Zn binding kinetics to the apical gill surface were studied in juvenile rainbow trout ( Oncorhynchus mykiss ). Two separate radiotracer techniques were employed to ascertain this information. First, in vitro binding kinetic experiments were performed at extremely elevated zinc concentrations (up to 20 mmol l−1) to measure relatively low-affinity binding sites at the gill epithelium. There were no differences in Zn binding parameters ( Km and B max) for fish sublethally exposed to Zn for 21 days and their simultaneous controls. Nevertheless, Ca did have an increased inhibitory effect on Zn binding in Zn-exposed fish suggesting that the anionic groups on the gill epithelium of these fish had been altered in some manner. Additionally, in vivo Zn binding kinetics were investigated using environmentally relevant waterborne Zn concentrations (low μmol l−1 range) to isolate high-affinity Zn binding sites (Ca transporters). No appreciable alterations in the Km and B max values for Zn binding were seen between the Zn-exposed group and its simultaneous control following 15 days of exposure. Furthermore, no significant differences in CC morphometry were observed between treatments. Despite these lack of treatment effects, there were temporal alterations in Km , B max and CC fractional surface area in both groups. It is proposed that these fluctuations are controlled by hormonal factors (such as stanniocalcin), believed to play a role in Ca influx.  相似文献   

16.
Stamen abscission and water balance in Metrosideros flowers   总被引:2,自引:0,他引:2  
Cymules (3-flowered units borne on single pedicels) were cut from inflorescences of Metrosideros collina J.R. & G. Forst. cv. Tahiti and used to test the effects of ethephon and ethylene on stamen abscission in the presence of silver thiosulphate (STS) and 1-methylcyclopropene (1-MCP), and to test the effects of holding solutions on cymule water balance and the progression of floral development. Flower bud and stamen abscission occurred in response to 0.5–5.0 and 0.1 μl l−1 ethylene, respectively. Ethylene effects were partially negated by scrubbing exogenous ethylene, and more completely negated by STS (2.0 m M ). 1-MCP caused greater ethylene production and inhibited stamen abscission for only 1–2 days after treatment. Ethephon (10-10 000 mg l−1) induced stamen wilting rather than abscission, an effect that was not negated by STS. Stamen wilting was negatively correlated with stamen relative water content, and the increase in stamen wilting was generally reduced by treatments that enhanced cymule mass. Stamen wilting was least using a 100 g l−1 sucrose pulse or holding solutions containing 30–40 g l−1 sucrose, with hydroxyquinoline citrate (200 mg l−1) maintained at pH 5. Our results indicate that 1-MCP may be relatively ineffective in blocking the effects of ethylene on the abscission of organs, such as the stamens of M . collina , which are highly sensitive to this hormone.  相似文献   

17.
Melatonin (MLT) was isolated from water samples using solid phase extraction cartridges and measured by radioimmunoassay. In tanks of rainbow trout Oncorhynchus mykiss , concentrations of MLT in water increased rapidly from <0·1 ng l−1 in the light phase to 0·7 ng l−1 in the dark giving calculated release rates of <1 ng kg−1 h−1 and 15 ng kg−1 h−1, respectively. This cycle in water MLT values corresponds to reported changes in plasma MLT concentrations. The colour of the tanks and a daytime acute handling stress did not affect concentrations of MLT in either the light or dark phase.  相似文献   

18.
Proliferating cultures of Actinidia deliciosa A. Chev., C. F. Liang and A. R. Ferguson cv. Tomuri (♂) were grown under photosynthetic photon flux density (PPFD) rates ranging from 30 to 250 μmol m−2 s−1 in order to determine certain physiological parameters in vitro: CO2 evolution, photosynthesis at three CO2 atmospheric concentrations (330, 1450 and 4500 μl l−1), fresh and dry matter accumulation and proliferation rate.
A proportional response in dry weight, dry/fresh weight ratios and PPFD was found. The proliferation rate increased up to 120 μmol m−2 s−1 but decreased at higher rates. At the highest PPFD, the CO2 released from cultures and accumulated in the vessels reached 200 μl l−1 of; at the lowest rate the CO2 concentration reached 10500 μl l−1 after 28 days of culture. The photosynthetic rate at 1450 and 4500 μl l−1 of CO2 was nearly 4 times higher than at the lowest concentration tested.  相似文献   

19.
Washed Escherichia coli ATCC11775 cells were killed by (–)-epigallocatechin (EGC) in the presence of a non- lethal concentration of Cu2+ (1 μmol l−1) without additional H2O2, but not by (–)-epicatechin (EC). EGC alone (< 0·1 mmol l−1) did not reduce the viability of the cells. The survival curve obtained in the presence of EGC and Cu2+ was similar to that obtained in the presence of (–)-adrenaline (EN) and Cu2+.  相似文献   

20.
Aim:  To study the effect of biosurfactant on aqueous phase solubility and biodegradation of chlorpyrifos.
Methods and Results:  A Pseudomonas sp. (ChlD), isolated from agricultural soil by enrichment culture technique in the presence of chlorpyrifos, was capable of producing biosurfactant (rhamnolipids) and degrading chlorpyrifos (0·01 g l−1). The partially purified rhamnolipid biosurfactant preparation, having a CMC of 0·2 g l−1, was evaluated for its ability to enhance aqueous phase partitioning and degradation of chlorpyrifos (0·01 g l−1) by ChlD strain. The best degradation efficiency was observed at 0·1 g l−1 supplement of biosurfactant, as validated by GC and HPLC studies.
Conclusion:  The addition of biosurfactant at 0·1 g l−1 resulted in more than 98% degradation of chlorpyrifos when compared to 84% in the absence of biosurfactant after 120-h incubation.
Significance and Impact of the Study:  This first report, to the best of our knowledge, on enhanced degradation of chlorpyrifos in the presence of biosurfactant(s), would help in developing bioremediation protocols to counter accumulation of organophosphates to toxic/carcinogenic levels in environment.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号