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1.
The prolonged effects of short-term action of N-methyl-N′-nitro-N-nitrosoguanidine (MNNG) in low concentrations 3 × 10?7 to 3 × 10?1 mg/l upon roach (Rutilus rutilus) early development have been studied. It was revealed that the treatment resulted in an increase in fish length and weight, in a decrease in total amylolytic and saccharase activities, and in different changes in parameters of di-and polysaccharide hydrolyses. The concentration-effect dependence is nonlinear. Both ultralow and the highest tested MNNG concentrations cause similar changes in carbohydrase activities and kinetic parameters of carbohydrate hydrolysis. The decrease in K m values of sucrose hydrolysis evidencing the increase in the enzyme to substrate affinity may be attributed to adaptive reactions of roach at early developmental stages in response to damaging embryotoxic action of MNNG in ultralow concentrations.  相似文献   

2.
Mutants resistant to diphtheria toxin (Dipr) have been selected from a variety of human fibroblast cell strains derived from both normal subjects and individuals with known genetic predisposition to cancer such as xeroderma pigmentosum, Fanconi anemia and Bloom's syndrome. Treatment with N-methyl-N′-nitro-N-nitrosoguanidine (MNNG) led to a marked increase in the frequency of Dipr mutants in various cell strains. The increase in the frequency of Dipr mutants occurred in a linear dose-dependent manner in response to MNNG and ethyl methanesulfonate, in one of the cell strains examined. The rate of muation to diphtheria toxin as determined by fluctuation analysis was very similar in various cell strains (1–3 × 10?7 mutations/cell/generation), except for the strain GM1492 (8.8 × 10?7 mutations/cell/generation) which is derived from a Bloom syndrome patient.  相似文献   

3.
Nitrate reductase (NO3R) activity, nitrite reductase (NO2R) activity and NADH2 dependent glutamate dehydrogenase (GDH) activity were followed in extracts from excised pea roots incubated under aseptic conditions for 9 and 24 h in nitrate containing nutrient medium to which IAA was added in concentrations promoting lateral root formation (1 × 10?5; 3 × 10?5; 5 × 10?5 M) and kinetin in concentrations which reduce lateral root formation (0.1; 1; 5 mg 1?1, that is 4.65 × 10?7;4.65 × 10?6 and 2.3 × 10?5 M). NO3R activity was not influenced by IAA, NO2R activity was slightly depressed by IAA after 24 h incubation and GDH activity was slightly increased after 24 h incubation in the presence of IAA. Kinetin decreased NO3R activity significantly both after 9 h and 24 h incubation, slightly increased NO2R activity after 9 h incubation but slightly decreased it after 24 h incubation, and did not affect GDH activity after 24 h incubation. However, when applied together with IAA, kinetin abolished the promoting effect of IAA on GDH activity. IAA neither reversed nor accentuated the effect of kinetin on NO2R activity. Nevertheless the depressing effect of kinetin on NO3R activity was emphasized by the presence of IAA after 9 h incubation. The results obtained indicate that reduced nitrate assimilation due to the depression of nitrate reductase activity caused by kinetin probably contributes to the negative growth effect of kinetin in pea root segments grown in nitrate medium.  相似文献   

4.
Spirodela polyrrhiza, a fast-growing duckweed with high starch and low lignin content, shows promise as a feedstock for bioenergy. Abscisic acid (ABA) is a biological hormone that controls plant growth and stress response. The effects of different ABA concentrations (0, 1.0 × 10?5, 1.0 × 10?4, 1.0 × 10?3, 1.0 × 10?2, and 1.0 × 10?1 mg/L) on duckweed biomass growth, carbon dioxide fixation, formation of photosynthetic pigments (Chlorophyll a (Chla), Chlorophyll b (Chlb), and carotenoids), the activities of soluble starch synthase (SSS) and starch branching enzyme (SBE), and the starch content of biomass were investigated in this study. ABA at concentrations lower than 1.0 × 10?3 mg/L promoted carbon dioxide fixation, whereas it inhibited carbon dioxide fixation at concentrations over 1.0 × 10?3 mg/L. ABA enhanced SSS and SBE activities at concentrations lower than 1.0 × 10?2 mg/L. ABA treatment increased the content of Chla, Chlb, and carotenoids and resulted in the enhancement of starch content. Chla content gradually increased with the increasing concentration of ABA (1.0 × 10?5 to 1.0 × 10?2 mg/L). After culturing for 10 days, starch content in 1.0 × 10?2 mg/L ABA medium reached 35.3% of dry weight (DW), which was the highest level in this study. This suggests that there is a great potential to develop a technology to increase starch accumulation in duckweed which can be used as an alternative to corn, sugarcane, or other food crops as a starch source.  相似文献   

5.
As a basis for devising an in vitro screening programme, culture conditions were optimized so that tissue cultures from two resistant cultivars of Brassica napus ssp. oleifera (Mikado, Bienvenu) and two susceptible cultivars (Lesira, Ceres) could be differentiated using a disease scoring scheme, when inoculated with Leptosphaeria maculans. Tissues inoculated included thin cell layer explants from soil-grown plants and in vitro-grown shoot cultures and callus tissue formed on such explants. The period of incubation and the incubation temperature were of importance in the development of differential disease reactions. Increasing temperature generally resulted in an increase in infection and too great an incubation period resulted in total overgrowth of the tissue. Increasing concentrations (1 × 10?6 M-1 ×10?4 M) of the auxins 1-naphthylacetic acid (NAA), 2,4-dichlorophenoxyacetic acid (2,4-D) and mdole-3-acetic acid (IAA) in the culture medium, resulted in a decrease in disease score of the thin cell layer (TCL) explants from soil-grown plants. The cytokinins examined 6-benzyl-aminopurine (BAP) and 6-4-hydroxy-3-methyl-2-enylaminopurine (zeatin), reduced the extent of infection of the TCL explants when used in combination with the auxin NAA. Medium containing NAA at a concentration of 1 × 10?6 M in combination with BAP at a concentration of 1× 10?6 or 1 × 10?4 M allowed differentiation of the disease reactions of the resistant and susceptible cultivars, when the explants were incubated for 10 days at 20 °C after inoculation. Similar conditions of incubation and the addition of NAA (1 × 10?6 M) combined with BAP (1 × 10?6 M) to the medium also allowed the differentiation of the disease reactions on TCL explants from stems of in vitro shoot cultures of the cultivars Mikado and Lesira. Increasing concentrations of the auxin NAA and the cytokinin BAP resulted in a reduction in the mean disease score of the callus tissue produced on TCL explants from soil-grown plants, and NAA (1 × 10?5 M) combined with BAP (1 × 10?6 or 1 × 10?5 M) allowed differentiation of resistance and susceptibility in callus tissues when incubated for 5 days at 20 °C. 2,4-D did not allow differentiation of the cultivars. This was in contrast to the inoculation of callus tissue attached to TCL explants of in vitro shoot cultures, where combinations of 2,4-D and BAP at concentrations of 1 × 10?6 M allowed differentiation of the resistant and susceptible cultivars. These findings provide a basis for designing selection protocols of value in both traditional as well as in vitro breeding programmes to select lines of oilseed rape with resistance/novel resistance to L. maculans.  相似文献   

6.
The mutability of the PN strain ofMycobacterium phlei was examined after induction of auxotrophic mutants and of STM and VM-resistant mutants, by UV irradiation. A total of 30 auxotrophic mutants were isolated, most of them amino acid-dependent five purine-dependent, and one uracil-dependent. To induce the mutants higher UV doses had to be used so that the survival of cells in the original suspension would not exceed a few per cent. For further genetic work use can be made of 8 auxotrophic mutants (PN try?ura?, PN arg?ura?, PN ileu?val?, PN ileu?, PN leu?, PN lys?, PN lys?-VMr, PN val?), these showing a low frequency of spontaneous reversions. No spontaneous auxotrophic mutants have been found. The frequency of STM and VM-resistant mutants is increased upon UV irradiation, a post-irradiation incubation in a liquid medium without the drug being essential for their phenotypic expression. The highest increase of the number of these mutants is attained after 48 h of post-irradiation incubation and it has been found that, within a certain experimental scatter, the same frequency increase is found on using a complete or a minimal liquid medium. The frequency of spontaneous STM-resistant mutants lies within 5.8×10?6–8.8×10?6, of those VM-resistant between 3.1×10?5 and 4.1×10?5. The highest frequency of induced STM-resistant mutants lies between 3.0×10?5 and 9.3×10?5 and of VM-resistant mutants between 1.1×10?4 and 2.2×10?4  相似文献   

7.
Nucleic acid can greatly enhance the fluorescence intensity of quercetin in HMTA‐HCl (pH 5.5) buffer. The enhanced intensity is in proportion to the concentration of nucleic acids in the range 5.0 × 10?9 to 1.0 × 10?6 g/mL for fsDNA, 5.0 × 10?9 to 7.0 × 10?7 g/mL for ctDNA and 5.0 × 10?9 to 1.0 × 10?6 g/mL for yRNA, and their detection limits (S/N = 3) are 3.5 × 10?9, 7.8 × 10?10 and 2.6 × 10?9 g/mL, respectively. In comparison with most reported fluorescent probes for the determination of nucleic acids, the proposed probe has higher sensitivity and lower toxicity. The interaction investigation indicates that quercetin binds with double‐strand DNA in groove binding mode, resulting in fluorescence enhancement of this system. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

8.
The addition of insulin (4.0 × 10?11 M) or acetylcholine (10?6 M) to isolated hepatocytes stimulated glycogen accumulation and this stimulation was more pronounced when the medium glucose was raised from 50 to 300 mg percent. Studies with [14C]-glucose showed a two-fold stimulation in glycogen synthesis by the addition of insulin (4.0 × 10?11 M) or acetylcholine (10?6 M). A sixteen percent increase in the activity of glycogen synthase was observed in cells incubated for 10 minutes with insulin (4.0 × 10?11 M) or acetylcholine (10?6 M), whereas at one hour incubation a 40 percent increase in activity was observed with the same concentration of insulin or acetylcholine. The effects of insulin and acetylcholine were not additive.  相似文献   

9.
Aims: A microbiological bioassay using Geoacillus stearothermophilus was optimized to detect betalactams at concentrations near to the Maximum Residue Limits (MRLs), with low cross‐specificity for tetracycline. Methods and Results: A factorial design (3 × 4) was used to evaluate the effects of concentration of spores (2·0 × 106, 4·0 × 106 and 8·0 × 106 spores ml?1) and incubation time (3·0, 3·5, 4·0 and 4·5 h) on the response of the bioassay. Then, desirability function to raise the detection capabilities (CCβ) of tetracyclines and increase sensitivity to betalactams was implemented. Significant effects of Log[S] and incubation time [It] on the CCβ of betalactams and tetracyclines were observed. Finally, high value of global desirability (D = 0·853), adequate betalactams CCβ (3·8 μg l?1 of penicillin ‘G’, 27 μg l?1 of oxacillin, 8·1 μg l?1 of ampicillin, 48 μg l?1 of cloxacillin) and high tetracyclines CCβ (5260 μg l?1 chlortetracycline, 1550 μg l?1 of oxytetracycline, 1070 μg l?1 of tetracycline) were calculated. Conclusions: The application of chemometric tools allows the optimization of a bioassay that detects betalactam residues in milk. The more robust conditions have been achieved in Log[S] = 6·30 and [It] = 4·20 h. Significance and Impact of the Study: The logistic regression model and the desirability function are adequate chemometric techniques to improve the properties of the methods, because it is possible to increase sensitivity and decrease cross‐specificity simultaneously.  相似文献   

10.
The migratory history of tapertail anchovy Coilia nasus in the Yangtze River Estuary, China was investigated using otolith Sr:Ca ratios and two-dimensional images of the Sr level from an X-ray electron probe microanalyzer (EPMA). The results showed that 17 of the 22 young-of-the-year (YOY) specimens had low Sr:Ca ratios (1.2–2.4?×?10?3;1.5?±?0.3?×?10?3) at the central otolith area, indicating their riverine origin and initial freshwater residence. In addition, 11 of the 14 adult specimens had low Sr:Ca ratios (1.3–2.2?×?10?3; 1.7?±?0.4?×?10?3) at the central otolith area but showed alternating changes between high (>4.0?×?10?3) and low (<2.5?×?10?3) values outside of this region, reflecting their riverine origin and the migration between freshwater and estuarine habitats. These 28 specimens represented the anadromous population in this region. The other 5 YOY specimens had high Sr:Ca ratios (3.6–5.9?×?10?3; 4.8?±?0.8?×?10?3) throughout the life history. Similarly, the other 3 adult specimens had high Sr:Ca ratios (4.0–5.7?×?10?3; 4.8?±?0.7?×?10?3) at the central otolith area but showed alternating changes between low and high values outside this region, suggesting that estuarine-origin non-anadromous individuals occurred in this region. The average of the otolith Sr:Ca ratios and Sr level mapping along the life-history transects could be used as a scalar for charting the migratory history of the tapertail anchovy in the Yangtze River Estuary: <2.0?×?10?3 for freshwater residence and 3.5–6.0?×?10?3 for estuarine residence.  相似文献   

11.
Hamster embryonic fibroblasts were treated directly with various concentrations of methylnitrosocyanamide (MNC), a nitrosated product of methylguanidine (MG) or N-methyl-N′-nitro-N-nitrosoguanidine (MNNG). Then they were examined for chromosomal aberrations, morphological transformation and mutations resistant to 8-azaguanine (8AG) and 6-thioguanine (6TG). Direct treatment with 2 to 10 × 10?6 M MNC caused a marked, dose-dependent appearance of 8AG- and 6TG-resistant mutations. The ability of MNC to induce mutations was similar to that of MNNG. Cultured embryonic fibroblasts in metaphase plates also showed a marked dose-dependent increase in chromosomal aberrations within 24 h after direct treatment with MNC of MNNG. Moreover, MNC and MNNG caused similar rates of morphological transformation.  相似文献   

12.
A novel chemiluminescence method for the determination of 6‐mercaptopurine was established based on 6‐mercaptopurine inhibition of the chemiluminescence emission of potassium permanganate–thioacetamide–sodium hexametaphosphate system. The peak height was proportional to log 6‐mercaptopurine concentration in the range 7.0 × 10?10 to 1.0 × 10?7 g/mL and the detection limit was 1.9 × 10?11 g/mL (S/N = 3). The relative standard deviation was 1.5% for the determination of 8.0 × 10?8 g/mL 6‐mercaptopurine (n = 11). The proposed sensor was successfully applied to the analysis of 6‐mercaptopurine in human serum samples. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

13.
In this paper, a sensitive resonance light scattering (RLS) method for the determination of protein is reported. In the Tris–HCl (pH 7.50) buffer, protein enhanced the RLS intensity of the Y3+–2‐thenoyltrifluoroacetone (TTA)–sodium dodecyl sulphate (SLS) system. The enhanced RLS intensities were in proportion to the concentrations of proteins in the range 8.0 × 10?9–1.0 × 10?5 g/mL for BSA, 1.0 × 10–8–1.0 × 10?5 g/mL for HSA and 1.0 × 10–8–1.0 × 10?6 g/mL for EA, and their detection limits were 5.0, 5.4 and 6.7 ng/mL, respectively. Actual samples were satisfactorily determined. The interaction mechanism was also studied. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

14.
14α-Hydroxymethyl-5α-cholest-7-en-3β-ol (I) and 14α-hydroxymethyl-5α-cholest-6-en-3β-ol (II) have been prepared by chemical synthesis from 3β-acetoxy-7α,32-epoxy-14α-methyl-5α-cholestane. Compound I, previously shown to be efficiently convertible to cholesterol upon incubation with rat liver homogenate preparations, has been found to be a potent inhibitor of sterol synthesis in animal cells in culture. Compound I caused a 50% reduction of the levels of HMG-CoA reductase activity in cultures of L cells and fetal liver cells at concentrations of 3 × 10?6 M and 8 × 10?6 M, respectively. Compound II, the Δ6-analogue of I, caused a 50% suppression of the enzyme activity in the two cell types at even lower concentrations, 5 × 10?7 M and 2 × 10?6 M, respectively. Concentrations of I and II required to specifically inhibit sterol synthesis from acetate were similar to those required to suppress the levels of HMG-CoA reductase activity.  相似文献   

15.
Rat submandibular gland was dissociated by enzymatic digestion with collagenase and hyaluronidase, followed by mild mechanical shearing and filtration through a nylon mesh. The dissociated cell populations contained predominantly groups of acinar cells which maintained their acinar arrangement. The morphological and functional viability of the cells was confirmed by electron microscopic examination and a normal secretory response to β-adrenergic or cholinergic stimulation was observed. Both isoproterenol (IPR) and carbachol caused the fusion of secretory granules into large vacuoles which were also continuous with the lumen, and into which the secretory product was released. Secretion was assessed quantitatively from the incorporation of 14C-glucosamine into the acinar cells and its subsequent release into the culture medium as labelled glycoprotein. IPR stimulated secretion to 125% of untreated controls in the concentration range 5 × 10?5 to 5 × 10?7 M, and to 110% of controls at 5 × 10?8 M, after 40 min incubation. Carbachol stimulated secretion to 131% of controls at 5 × 10?5 M and to 115% at 5 × 10?6 M but had no effect at 5 × 10?7 or 5 × 10?8 M. The secretory response was blocked by the respective β-adrenergic and cholinergic antagonists, propranolol and atropine. These findings show that dissociated rat submandibular acinar cells provide a useful in vitro model for the study of mucus synthesis and secretion.  相似文献   

16.
A procedure has been developed to measure maximal packet size for serotonin in vesicles of intact, washed human platelets. Vesicles were trace-labelled with H3-5HT and subsequently permitted to accumulate larger amounts of C14-5HT from the extracellular medium. Parallel platelet aliquots were incubated with unlabelled 5HT, and total and thrombin-releasable 5HT were measured by an enzymatic assay. Prior to incubation, 5HT packet size ranged from 0.05 to 0.53 × 10?17 moles/platelet. No net addition of 5HT to vesicles occurred when this compartment contained more than 2–3 × 10?17 moles/platelet of 5HT, suggesting that maximal packet size was 2.8 × 10?17 moles/platelet. Under these conditions, a typical vesicle would contain 4 × 10?18 molesof 5 HT, at an estimated concentration of 0.6 M. Nevertheless, when vesicles were full, they continued to exchange C14-5HT from the extracellular medium with H3-5HT sequestered in vesicles.  相似文献   

17.
By using the static correlations of fluctuations in the dihedral angles of the α-helices of polyglycine and poly(L -alanine) calculated previously, geometrical fluctuations of a section (consisting of up to 18 peptide units) of the α-helices of infinite length are calculated. These fluctuations are found to differ in some respects (e.g., the dependence of amplitudes on the length of section) from those of a circular rod made of homogeneous continuous material. However, the moduli of the mechanical strengths (tensile Young's modulus, bending Young's modulus, and the shear modulus) of a circular rod are calculated, whose geometrical fluctuations are approximately equal to the fluctuations of a section consisting of 18 peptide units. They are of the order of 1011 dyn/cm2. The tensile rigidity, flexural rigidity, and torsional rigidity are calculated to be 1.20 × 10?3 dyn, 2.46 × 10?19 dyn·cm2 and 1.79 × 10?19 dyn·cm2 for polyglycine, and 1.96 × 10?3 dyn, 4.05 × 10?19 dyn·cm2 and 3.28 × 10?19 dyn·cm2 for poly(L -alanine), respectively.  相似文献   

18.
Capecitabine is a chemotherapeutic agent used for the treatment of patients with metastatic cancers. This study aimed at determining the drug capecitabine in a simple chemiluminescence (CL) system of acidic potassium permanganate using the stopped‐flow injection technique. Statistical methods were used to detect optimum conditions. The method showed two linear calibration ranges from 6.7 × 10?6 to 6.7 × 10?5 mol L?1 and from 6.7 × 10?5 to 2.7 × 10?3 mol L?1 with a detection limit of 1.5 × 10?6 mol L?1. Chitosan‐modified magnetic nanoparticles were studied in the drug‐delivery experiments. According to the pH sensitivity of chitosan and low pH values in tumour cells, the chitosan‐coated magnetic nanoparticles could provide a good targeting drug‐delivery system to tumour sites. To evaluate the applicability of the method, the capecitabine‐loaded magnetic chitosan nanoparticles were synthesized with two different cross‐linkers; loading and releasing rates of the drug were investigated using the proposed CL method and an ultraviolet–visible light spectrophotometric method (absorption at 305 nm). The results showed a good correlation between the two methods, and it was found that the synthesized chitosan‐modified magnetic nanoparticles could be used for pH‐dependent release of capecitabine in cancer cells. Moreover, determination of capecitabine in tablets and synthetic samples was performed.  相似文献   

19.
The formaldehyde method was used to examine the interaction of PGE1 with morphine, β-endorphin and Met-enkephalin on rat mast cells by their effects on IgE-mediated 14C-serotonin release. PGE1 (2×10?8?2×10?5 M) caused a dose-related inhibition of the mediator release 1 min after an antigen challenge, and morphine (3×10?7?3×10?5 M) reversed this PGE1 effect dose-dependently and stereospecifically; naloxone (2×10?4 M) antagonized this action of morphine. β-Endorphin (3×10?7?10?5 M) and Met-enkephalin (3×10?6?10?4 M) mimicked this morphine action dose-dependently and were antagonized by naloxone (2×10?4 M). These results suggest that morphine and endorphins modulate immunological mediator release from rat mast cells through opioid receptors.  相似文献   

20.
Dichlorodiphenyltrichloroethane (DDT), hexachlorocyclohexane (HCH), and their isomers’ levels in residential soils were determined for the assessment of health risk in Korba, India. Observed concentrations of total HCH and total DDT in soils were more or less comparable with other parts of India and the world. ΣHCH and ΣDDT concentrations ranged between 0.9–20 μg kg?1 and 2–315 μg kg?1, respectively, which were lower than recommended soil quality guidelines indicating low ecotoxicological risk. Carcinogenic and non-carcinogenic impacts of HCH and DDT on human populations through soil ingestion were evaluated and presented. The incremental lifetime cancer risk (ILCR) for adults and children ranged between 7.8 × 10?10–1.6 × 10?7 and 4.1 × 10?9–8.2 × 10?7, respectively. Non-cancer health hazard quotient (HQ) ranged between 5.9 × 10?7–1.8 × 10?3 and 3.1 × 10?6–9.4 × 10?3, respectively, for adults and children. The estimated ILCR and HQ were within the safe acceptable limits of 10?6–10?4 and ≤1.0, respectively, indicating low risk to human populations from exposure to organochlorine pesticides (HCH and DDT) in the study area.  相似文献   

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