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51.
52.
Kenji Kato Su-wan Oh Hiroyuki Yamamoto Takayuki Hanazato Ikuko Yasuda Akira Otuki Masayuki Takahashi 《Ecological Research》1992,7(3):267-276
In order to understand the control mechanisms of a large, stable bacterial standing stock, enclosure experiments were conducted
in a eutrophic lake, where both bacterial productivity and grazing pressure were very high. Total bacterial number in the
different enclosures ranged from 1.2 to 2.7×107 cells mL−1 throughout the experiment. The average bacterial cell production rate estimated from a grazer eliminating experiment was
6.3×105 cells mL−1 h−1. Difference in the bacterial cell production rate between shaded and unshaded enclosures was not apparent. Bacteria showed
a reduction in standing stock of only about 25–30% even after the supply of light was cut to 1%. Bacteria in the shaded enclosures
then recovered their production rate in the first 12 days of perturbation. Grazing pressure in the shaded enclosures was not
less than that for the control. Thus, it was considered a control mechanism of bacterial stable standing stock that the bacteria
shifted their organic substrate from extracellular dissolved organic carbon freshly released from phytoplankton to that already
stocked in the water column, though it is not known whether the dominant bacteria were the same. 相似文献
53.
Mutagenicity of 30 chemicals in Salmonella typhimurium strains possessing different nitroreductase or O-acetyltransferase activities 总被引:2,自引:0,他引:2
Salmonella typhimurium YG1021, YG1024, YG1026 and YG1029 are new derivatives of the Ames tester strains TA98 and TA100, with elevated 'classical' nitroreductase or acetyl-CoA:N-hydroxyarylamine O-acetyltransferase level. Thirty mutagens with different structures were tested using these strains and the sensitivities were compared with those of the conventional strains and of the enzyme-deficient strains. Elevated O-acetyltransferase activity of the indicator strains specifically increased their ability to detect the mutagenicity of aromatic nitro, amino and hydroxylamino compounds, whereas the strains with high nitroreductase activity were very sensitive to some nitroaromatics. The combined use of the isogenic tester strains with different metabolic capacities was quite useful to assess the intracellular metabolic activation and detoxification mechanisms of chemical mutagens. 相似文献
54.
The degree of intergradation between two species of Sulawesi macaques,Macaca tonkeana andM. hecki, was studied by examining the diagnostic external characteristics of more than 100 monkeys kept as pets by natives. Two possible
hybrid monkeys were found and both originated from the borderland between the two species, located in the most proximal region
of the northern peninsula of Sulawesi. The previously postulated wide area of integradation between the two species at the
possible contact zone was, however, not recognized, and typical examples oftonkeana orhecki were found to be present on the two sides of a narrow “hybrid” zone which was defined by direct observations. Furthermore,
despite considerable individual variations, we were able to allocate most monkeys to one or other of the species. Each of
ten external characteristics of the members of both species more or less encompassed the individual variations, but may undergo
changes with the development of the monkeys. The mechanisms of reproduction of hybrid monkeys and the maintenance of differences
between the species are discussed. 相似文献
55.
Keiko Mori Kazuho Hirata Masaru Kawabuchi Manabu Nakashima Takeshi Watanabe 《Immunogenetics》1991,33(2):101-107
A monoclonal antibody (mAb) TP-3 has been established by immunizing rats with the BALB/c mouse thymic epithelial cell line TEL-2. The TP-3 antigen is expressed on stroma cells of thymus, spleen, and lymph node in syngeneic BALB/c mice (H-2
d
). This antigen is also expressed at a low level on the cell surface of immature thymocytes, and at a high level on mature T and B cells. In allogeneic mice such as C57BL/6 (H-2
b
) or C3H (H-2
k
), no cells expressed the TP-3 antigen. Using H-2 congenic mice, reactivity with mAb TP-3 was found to map to a region of H-2D
d
L
d
or between D
d
and Qa, suggesting that TP-3 is a major histocompatibility complex (MHC) class I antigen. However, immunoprecipitation analysis indicated that this antigen is not identical to the classical mouse class I molecules in terms of molecular size, antigenicity, and tissue distribution. 相似文献
56.
A biosensor system for continuous flow determination of plural enzyme activities was prepared from the combination of two pyruvate sensors, a prereactor and a flow cell. This system was applied to the simultaneous determination of lactic dehydrogenase (LDH) and glutamic-pyruvic transaminase (GPT) activities in the same sample. These enzyme activities can be determined by measuring pyruvate produced by the enzyme reactions as follows. The amount of pyruvic acid can also be determined from the amount of oxygen consumed upon oxidation of pyruvic acid by pyruvate oxidase. (Formula: see text). Therefore, both of the detectors for the determination of lactic dehydrogenase and glutamic-pyruvic transaminase activities were prepared from the combination of a pyruvate oxidase membrane and an oxygen electrode. Pyruvate oxidase was covalently immobilized on a membrane prepared from cellulose triacetate. A linear relation was obtained between the output current and LDH or GPT activities in the range of 50 to 3,600 IU l-1 or 6 to 1,000 IU l-1, respectively. Each assay of these enzyme activities was completed within 15 min. The results obtained had a precision of ca. 4%. The sensor was stable for more than 25 days at 5 degrees C. 相似文献
57.
Kiyoshi Matsuura Masayuki Takasugi Yasumasa Kunifuji Akio Horie Akio Kuroiwa 《Biological trace element research》1991,31(2):171-182
Twenty-four male rats of the Wistar strain divided into four groups were injected sc with a dose of 0.8, 1.5, and 3.0 mg Cd/kg body wt as CdCl2 in saline, and saline alone to the control rats, three times a week for 3 wk. Cadmium levels of whole kidney homogenate, supernatant (cytosol), precipitate, and metallothionein (MT) fraction were measured. Histological changes of the renal proximal tubules were investigated by optical and electron microscopy. In the kidneys, Cd levels were increased with the increment of Cd dosage; 80–90% of Cd was contained in cytosol, and 55–75% was in MT fraction. Non-MT-Cd reached a maximum in the 1.5 mg Cd group, whereas that of the 3.0 mg Cd group showed some decline. With increasing Cd doses, the size of nuclei and nucleoli in the cells of proximal tubule showed significant enlargement and also an increase in the number of nucleoli on light microscopy. At higher doses, chromatin condensation of the tubular nuclei and vacuolar degeneration of the tubular cells were evident. On electron microscopy, perichromatin granules of the proximal tubular nuclei were increased in number, especially in the rats of Cd 0.8 mg and 1.5 mg/kg groups. As the Cd doses increased, ring-shaped nucleoli were increased in number and nucleolar segregation was observed more clearly. Moreover, in the 3.0 mg/kg Cd group, nuclear indentation and nucleoli containing compact dense granules were observed. In the cytoplasm, there was an increase of lysosomes, myelin bodies, ring-shaped mitochondria, and vesiculation; ultimate changes were degeneration and cell necrosis. The injured cells were heterogenously distributed in each nephron and this heterogeneity was attributed in the difference in Cd content and cell cycle in each cell of the nephron. 相似文献
58.
Photoautotrophic and photomixotrophic growth of strawberry plantlets in vitro and changes in nutrient composition of the medium 总被引:3,自引:0,他引:3
T. Kozai K. Iwabuchi K. Watanabe I. Watanabe 《Plant Cell, Tissue and Organ Culture》1991,25(2):107-115
Explants excised from strawberry (Fragaria x ananassa Duch.) plantlets were cultured in vitro for 21 days on half-strength MS (Murashige & Skoog 1962) basal liquid medium with 20 g l-1 sucrose and without sugar in the vessels capped with gas permeable microporous polypropylene film. The experiments were conducted under CO2 nonenriched (350–450 mol mol-1 in the culture room) and CO2 enriched (2,000 mol mol-1 during the photoperiod in the culture room) conditions with a PPF (photosynthetic photon flux) of 200 mol m-2 s-1. The CO2 concentration in the vessels decreased to approximately 200 mol mol-1 during the photoperiod on day 21 under CO2 nonenriched conditions. The fresh and dry weight, net photosynthetic rate (NPR) per plantlet, NPR per g leaf fresh weight, NPR per g leaf dry weight, the number of unfolded leaves, and ion uptake of PO4
3-, NO3
-, Ca2+, Mg2+ and K+ on day 21 were the greatest under photoautotrophic (no sugar in the medium) and CO2 enriched conditions. The residual percent of PO4
3- was 3% on day 21 under photoautotrophic and CO2 enriched conditions.Abbreviations MS
Murashige & Skoog (1962) basal medium composition
- NPR
net photosynthetic rate
- PPF
photosynthetic photon flux 相似文献
59.
Masato Terasawa Masayuki Inui Yasukazu Uchida Miki Kobayashi Yasurou Kurusu Hideaki Yukawa 《Applied microbiology and biotechnology》1991,34(5):623-627
Summary The application of an inducible regulation system using the trytophanase operon promoter (TPase promoter; Ptna) was examined for its high expression of the tryptophan synthase (TS) gene in Escherichia coli. The main problem in the application of Ptna for industrial purposes is catabolite repression by glucose, since glucose is the most abundant carbon source. However, this problem could be avoided by changing glucose to an organic acid, such as succinate, fumarate, malate and acetate, in the course of cultivation after glucose initially added was completely consumed. Under these conditions, l-tryptophan was also used to induce tryptophan synthase. Thus, the specific activity of TS in E. coli strain no. 168 harbouring pBR322F-PtnaTS was increased 500-fold compared to that of the cultured host strain. About 1 mol l-tryptophan/l reaction mixture was formed from indole and l-serine at 37° C for 3.5 h.
Offprint requests to: H. Yukawa 相似文献
60.
R Y Osamura Y Suemizu S Yoshimura S Hori K Inada K Watanabe Y Nakai H Imura 《Peptides》1991,12(3):503-507
In order to elucidate the relationship between secretory pathway and processing for precursor molecule of peptide hormones, we performed immunoelectron microscopic studies to localize POMC-derived peptides in mouse cultured L cells (fibroblasts without secretory granules) and in mouse AtT20 cells (ACTH secreting pituitary tumor cells with secretory granules) which had been transformed with human POMC gene. From the electron microscopic localization patterns, L42 cells were considered to serve as a model of constitutive pathway without processing of POMC, and A53 cells were considered to serve as a model of transgranular (regulated) pathway with processing of POMC. Immunoblotting supported these interpretations. 相似文献