17β-Hydroxysteroid dehydrogenase activity in endometrial cancer cells: Different metabolic pathways of estradiol in hormone-responsive and non-responsive intact cells

In this paper we report that two human long-term endometrial cancer cell lines, Ishikawa and HEC-1A, exhibit quite different abilities in metabolizing estrogens. As a matter of fact, incubation of Ishikawa cells with close-to-physiological concentrations of estradiol (E₂) as precursor resulted in: (1) elevated formation (up to 90%) of E₂-sulphate (E₂-S), using lower precursor concentrations; (2) very limited conversion to estrone (E₁) (< 10% at 24 h incubation), as either free or sulphate; and (3) low but consistent production of other estrogen derivatives, such as 2-hydroxy-estrogens and estriol. Conversely, scant amounts (if any) of E₂-S were found in HEC-1A cells, while no detectable formation of other estrogen metabolites could be observed after 24 h. On the other hand, E₁ production was significantly greater (nearly 60% at 24 h) than in Ishikawa cells, a large proportion of E₁ (over 50% of the total) being formed after only 6 h incubation using time-course experiments. The hypothesis that E₂ metabolism could be minor in Ishikawa cells as a consequence of the high rate of E₂-S formation encountered is contradicted by the evidence that conversion to E₁ also remains limited in the presence of much lower E₂-S amounts, seen using higher molar concentrations of precursor. Overall, we observe that 17β-hydroxysteroid dehydrogenase (17β-HSD) activity diverges significantly in intact Ishikawa and HEC-1A endometrial cancer cells. This difference could not merely be accounted for by the diverse amounts of substrate (E₂) available to the cells, nor may it be imputed to different levels of endogenous estrogens. It should rather be sought in different mechanisms controlling 17β-HSD activity or, alternatively, in the presence of distinct isoenzymes in the two different cell types.     

拟南芥微丝加帽蛋白β亚基参与壳梭孢素诱导的气孔开放过程

气孔是植物响应外源信号,与环境进行水分和气体交换的门户。由外源信号引起的保卫细胞微丝骨架动态变化在气孔运动中发挥重要作用,但是具体的精确调节机制仍不清楚。微丝结合蛋白家族(ABPs) 是微丝动态组装最直接的调控者,它们的作用不容忽视。本文运用反向遗传学,以微丝结合蛋白—加帽蛋白 (CP) β-亚基 (CPB) 突变体cpb-3为实验材料,探究其在壳梭孢素 (FC)诱导气孔开放中的作用。结果发现:离体叶片干燥3 h,cpb-3突变体的叶片失水率为63.45%,明显高于野生型的48.99%。气孔开度测量及激光共聚焦显微镜观察发现,cpb-3突变体的气孔开放程度以及微丝动态重排对FC分子更敏感。气孔开度相比野生型增大了20% (P<0.05),含辐射状微丝排布的保卫细胞数量比例增幅达到58.3%,比对照组高出18.5%。此外,非损伤微测技术记录保卫细胞Ca²⁺、K⁺等跨膜运输动态,FC处理下,cpb-3突变体保卫细胞中Ca²⁺外流速度升至212.86 pmol cm^-2s^-1,野生型仅为68.76 pmol cm^-2s^-1,明显快于野生型。且K⁺内流也有相同表现。综上表明,微丝加帽蛋白CP的β亚基CPB可能通过调节保卫细胞微丝骨架动态重排以及离子流动,在FC诱导的气孔运动中发挥重要的作用。     

Clusterin over-expression modulates proapoptotic and antiproliferative effects of 1,25(OH)2D3 in prostate cancer cells in vitro

Prostate cancer is the most commonly diagnosed cancer in the majority of western countries. Due to their antiproliferative and proapoptotic activity, vitamin D analogues have been introduced recently as an experimental therapy for prostate cancer. Clusterin (CLU) is a glycoprotein that has two known isoforms generated in human cells. A nuclear form of CLU protein (nCLU) is pro-apoptotic, and a secretory form (sCLU) is pro-survival. In this study, we analyzed whether proapoptotic and antiproliferative effects of 1,25(OH)₂D₃ on LNCaP prostate cancer cells are modulated by expression of sCLU. Using colony forming assay, we studied the effect of treatment with different doses of 1,25(OH)₂D₃ (10⁻⁶, 10⁻⁷, 10⁻¹⁰ M) on proliferation of LNCaP cells that were stable transfected and over-express sCLU (LNT-1) as compared to empty vector-transfected cells (LN/C). We also measured apoptosis using TUNEL assay. sCLU over-expression protected against both antiproliferative (30%) and proapoptotic (15%) effects of 1,25(OH)₂D₃, although this effect was statistically not significant. In conclusion, our findings demonstrate that expression of sCLU modulates growth regulatory effects of 1,25(OH)₂D₃ in prostate cancer indicating that CLU interferes with vitamin D signalling pathways.     

Autoradiographic Differentiation of Tritium and Another β-Emitter by A Combined Colour-Coupling and Double Stripping-Film Technique

This technique distinguishes cells labelled with ³H, with ₁₄C, or with both isotopes together, in the same histological preparation. The technique depends on the application of two layers of autoradiographic stripping film, separated by a thin layer of celloidin. The first layer (in contact with the tissue) records predominantly the distribution of ³H in the sample, the second exclusively that of ¹⁴C. The silver grains in one layer are coloured by dye-coupling, which enables the grains in the two layers to be differentiated without the need for separate focussing. The merits of stripping film over liquid emulsion are: rigid control of the thickness and uniformity of the film is assured; an inert celloidin layer of 0.1 μ or less can be applied between the two films; and the thickness of each film can be chosen to suit emission characteristics of the radioisotopes.     

Transport of G AB A, β-Alanine and Glutamate into Perikarya of Postnatal Rat Cerebellum

Abstract: Cells dissociated from the postnatally developing rat cerebellum retain their high-affinity carrier-mediated transport systems for [³H]GABA ( K _t=1.9 μM, V = 1.8 pmol/10⁶ cells/min) and [³H]glutamate ( K _t= 10 μM, V = 7.9 pmol/10⁶ cells/min). Using a unit gravity sedimentation technique it was demonstrated that [3H]GABA was taken principally into fractions that were enriched in inhibitory neurons (Purkinje, stellate and basket cells). [³H]β-alanine (which is taken up specifically by the glial GABA transport system) and [³H]glutamate were concentrated by glial-enriched fractions. However [³H]glutamate uptake was minimal in fractions enriched in precursors of granule cells, which may utilise this amino acid as their neurotransmitter. These results are discussed in relation to reports of high-affinity [³H]glutamate uptake by glia. The role of glutamate transport in glutamatergic cells is also considered. The data suggest that high-affinity glutamate transport is a property of glial cells but not granule neurons.     

Determination of turnover of androstenedione to estrone via aromatase in estrogen receptor positive and negative human breast cancer cell lines [Poster 48]

In one estrogen receptor (ER) negative (MDA-MB-231) and two ER positive human breast cancer cell lines (T-47-D,SK-BR-3) we measured aromatase activity by [³H]water assay and estrone (E1) production by thin-layer chromatography. Compared with ether extraction and charcoal method, lyophilization proved to be the most sensitive technique to measure the quantity of [³H]water. The extremely low contamination of the water soluble phase by [1ß-³H]androstenedione (0.02%), as well as the lack of errors due to conjugated steroids, offers the possibility to measure changes of cellular aromatase activity even at very low levels. In contrast to SK-BR-3 and MDA-MB-231 cells, we found no aromatase activity in T-47-D cells. There was no coincidence between ER status and aromatase activity. Proliferation of tumor cells was parallel with a continuous increase of aromatase activity and E1 production during mitogenic growth phase reaching highest levels at the transition from log to plateau-phase.     

甜菜夜蛾半胱天冬酶基因的克隆及对细胞凋亡诱导剂和病原微生物感染的表达响应

[目的]本研究旨在明确甜菜夜蛾Spodoptera exigua半胱天冬酶(caspase)在细胞凋亡诱导剂诱导和病原微生物胁迫下的表达模式,为丰富鳞翅目昆虫细胞凋亡机制研究奠定基础.[方法]利用RT-PCR技术从甜菜夜蛾3龄幼虫体内扩增两个半胱天冬酶基因(SeCasp-3和SeCasp-4)编码区的全长;利用qPCR...     

Aromatase in bone: roles of Vitamin D3 and androgens

We have mainly focused on the regulatory mechanism of cytochrome P450 aromatize in bone cells. Our previous study demonstrated a strong positive correlation of serum dehydroepiandrosterone sulfate (DHEA-S) and estrone (E1) with BMD in postmenopausal women but no correlation between serum estradiol (E2) and BMD in the same group. In addition, administration of DHEA to ovariectomized rat significantly increased BMD. These in vivo findings strongly suggested that circulating adrenal androgen may be converted to estrogen in osteoblast and may contribute to BMD maintenance. Actually, in cultured human osteoblast cells, DHEA was found to convert to androstenedione by 3β-hydroxysteroid dehydrogenase (3β-HSD) activity and then androstenedione to estrone through the apparent aromatase activity. The aromatase activity in cultured human osteoblast cells was significantly increased by dexamethasone (DEX). Interestingly, DEX and 1,25-dihydroxyvitamin D₃ (VD₃) synergistically enhanced aromatase activity as well as P450arom mRNA expression. A little stronger induction of aromatase activity by DEX and VD₃ was observed in cultured human fibroblasts. The increase of the aromatase activity by DEX and VD₃ was accompanied with the increase of luciferase activity of fibroblast cells transfected with Exon 1b-promoter-luciferase construct, but not of osteoblasts transfected with the same construct, suggesting a different regulatory mechanism of aromatase by DEX and 1,25-dihydroxyvitamin D₃ (VD₃) between these two cells despite the same promotor usuage. In human bone cells, intracrine mechanism through aromatase activity, together with a positive regulation of aromatase activity by glucocorticoid and VD₃, may contribute to the local production of estrogens, thus leading to protective effect against osteoporosis especially after menopause. The effect of sex steroids (estrogen versus testosterone) in bone remodeling was also briefly reviewed based on several recent findings in this field.     

Immunogold localization of photosynthetic enzymes in leaves of Aristida latifolia, a unique C4 grass with a double chlorenchymatous bundle sheath

C₄ species of the genus Aristida (Poaceae) have 3 distinct types of photosynthetic cells in their leaves, the mesophyll (M) cells, the outer bundle sheath (BS) cells, and the inner BS cells, and exhibit a unique Kranz-type leaf anatomy. The cellular localization of C₃ and C₄ photosynthetic enzymes was investigated in leaves of Aristida latifolia Domin by the protein A-gold immunocytochemical technique. The outer BS cells contained centripetally located small chloroplasts, which were structurally similar to those of the M cells. The inner BS cells contained centrifugally located large chloroplasts, which lacked well-developed grana and exhibited rudimentary grana for the most part. The leaves contained high levels of NADP-malic enzyme (EC 1.1.1.40) activity, and the plant was classified as being of the NADP-malic enzyme type. The immunocytochemical study revealed that labeling of ribulose 1,5-bisphos-phate carboxylase/oxygenase (EC 4.1.1.39) was present in the chloroplasts of the outer and inner BS cells, but was undetectable in the M cells. Labeling of phoshoen-olpyruvate carboxylase (EC 4.1.1.31) was observed in the cytosol of M cells, but not in that of BS cells. By contrast, labeling of pyruvate, P_i dikinase (PPDK, EC 2.7.9.1) was evident not only in the chloroplasts of M cells but also in those of outer BS cells, but was absent from the inner BS cells. The density of labeling in the chloroplasts of M cells was higher than that in chloroplasts of outer BS cells. These results indicate that the two carboxylating enzymes are differentially distributed between the M cells and the two types of BS cells, whereas PPDK shows a more complex distribution pattern. The locations of these enzymes are discussed in relation to C₄ photosynthesis.     

Hyaluronidase in sera of tumour-bearing nude mice

Cancer cell lines often secrete hyaluronidase, suggesting that this enzyme could be used as a marker of growing tumours. We have measured hyaluronidase in the sera of non-grafted mice and mice grafted with human tumour-derived hyaluronidase-secreting H460M and SA87 cells or non-secreting CB 193 cells. Mouse serum hyaluronidase was measured at pH 3.8 using the enzyme-linked sorbent assay (ELSA) technique by reference to human serum whose activity at pH 3.8 was determined by the Reissig technique. The serum hyaluronidase in non-grafted mice ranged from 310-520 mU l^-1 (mean±SD 432±70 mU l^-1, median 440 mU l^-1). Hyaluronidase increased in the sera of tumour-bearing mice grafted with H460M cells or with SA87 cells, but not in the sera of mice grafted with CB 193 cells. Serum hyaluronidase activity in H460M or SA87 tumour-bearing mice correlated with the tumour mass, increased with time, and decreased after tumour removal. Zymography detected two different hyaluronidase forms in the sera of non-grafted mice: type 1 had only one hyaluronidase band and type 2 had five different bands. In both types, enzyme augmentation in tumour-bearing mice correlated with the presence of an additional enzyme band that was not seen in normal sera and that migrated as the cancer cell enzyme did; there was no augmentation of the normal isoform(s). These results show that serum hyaluronidase can be used to follow the development of tumours in mice grafted with hyaluronidase-secreting cells.     

Long-term oxidant deficiency in Pseudomonas aeruginosa PAO303 results in cells which are non-culturable under aerobic conditions

Abstract The effect of long-term energy starvation (lack of electron acceptor in respiration) on the culturability of Pseudomonas aeruginosa PAO303 was studied by subsequent incubations for growth on aerobic medanaerobic media. A batch culture was grown on O₂-free citrate minimal medium containing NO₃⁻ as oxidant. Stationary phase was reached when NO₃⁻ was exhausted. This was followed by a rapid loss of cell culturability as tested by aerobic growth on agar plates (colony forming units, cfu) or on 0.2 μm membrane filters (epifluorescence technique) using the citrate minimal medium. However, energy-starved cells could form ten times more colonies when incubated anaerobically with NO₃⁻ (denitrifying conditions) than when incubated aerobically. Hence the energy starvation resulted in a subpopulation of cells, which were detectable under denitrifying, but not under aerobic growth conditions.     

Application of confocal laser scanning microscopy to detect oxidative stress in human colon cells

Introduction Excess of intracellular reactive oxygen species in relation to antioxidative systems results in an oxidative environment which may modulate gene expression or damage cellular molecules. These events are expected to greatly contribute to processes of carcinogenesis. Only few studies are available on the oxidative/reductive conditions in the colon, an important tumour target tissue. It was the objective of this work to further develop methods to assess intracellular oxidative stress within human colon cells as a tool to study such associations in nutritional toxicology.

Methods We have measured H₂O₂-induced oxidative stress in different colon cell lines, in freshly isolated human colon crypts, and, for comparative purposes, in NIH3T3 mouse embryo fibroblasts. Detection was performed by loading the cells with the fluorigenic peroxide-sensitive dye 6-carboxy-2',7'-dichlorodihydrofluorescein diacetate (diacetoxymethyl ester), followed by in vitro treatment with H₂O₂ and fluorescence detection with confocal laser scanning microscopy (CLSM). Using the microgel electrophoresis (“Comet”) Assay, we also examined HT29 stem and clone 19A cells and freshly isolated primary colon cells for their relative sensitivity toward H₂O₂-induced DNA damage and for steady-state levels of endogenous oxidative DNA damage.

Results A dose-response relationship was found for the H₂O₂-induced dye decomposition in NIH3T3 cells (7.8-125 μM H₂O₂) whereas no effect occurred in the human colon tumour cell lines HT29 stem and HT29 clone 19A (62-1000 μM H₂O₂). Fluorescence was significantly increased at 62 μM H₂O₂ in the human colon adenocarcinoma cell line Caco-2. In isolated human colon crypts, the lower crypt cells (targets of colon cancer) were more sensitive towards H₂O₂ than the more differentiated upper crypt cells. In contrast to the CLSM results, oxidative DNA damage was detected in both cell lines using the Comet Assay. Endogenous oxidative DNA damage was highest in HT29 clone 19A, followed by the primary colon cells and HT29 stem cells.

Conclusions Oxidative stress in colon cells leads to damage of macromolecules which is sensitively detected in the Comet Assay. The lacking response of the CLSM-approach in colon tumour cells is probably due to intrinsic modes of protective activities of these cells. In general, however, the CLSM method is a sensitive technique to detect very low concentrations of H₂O₂-induced oxidative stress in NIH3T3 cells. Moreover, by using colon crypts it provides the unique possibility of assessing cell specific levels of oxidative stress in explanted human tissues. Our results demonstrate that the actual target cells of colon cancer induction are indeed susceptible to the oxidative activity of H₂O₂.     

M1 Muscarinic Receptors Stimulate Rapid and Prolonged Phases of Neuronal Nitric Oxide Synthase Activity: Involvement of Different Calcium Pools

Abstract: This study shows that activation of M₁ muscarinic receptors, when coexpressed in Chinese hamster ovary (CHO)-K1 cells with neuronal nitric oxide (NO) synthase (nNOS), produces early and late phases of elevation of both intracellular Ca²⁺ concentration and nNOS activity. We examined the relationship between receptor-mediated increases in intracellular Ca²⁺ concentration and activation of nNOS over both short and long intervals using guanosine 3',5'-cyclic monophosphate (cGMP) formation as a measure of nNOS activity. The rapid phase of nNOS activation was dependent on release of Ca²⁺ from intracellular stores in both the CHO M₁/nNOS transfected cells and in neuroblastoma (N1E-115) cells, in which muscarinic receptors and nNOS are endogenously expressed. Two single point mutations in the M₁ muscarinic receptor that have previously been shown to uncouple differentially the receptor from phosphoinositide hydrolysis produced parallel attenuation of the rapid phase of nNOS activation. Characterization of the prolonged phase of nNOS activation was done using the conversion of l -[³H]arginine to l -[³H]citrulline as well as cGMP formation following stimulation of M₁ muscarinic receptors for 60 min. Both responses were dependent on influx of extracellular Ca²⁺ and were accompanied by prolonged formation of NO at functionally effective levels as late as 60 min following receptor activation. Therefore, this study demonstrates for the first time the existence of two mechanistically distinct phases of nNOS activation that are dependent on different sources of Ca²⁺.     

Double labelling of tissue combining tritiated thymidine autoradiography with immunodetection of bromodeoxyuridine: the autoradiographic significance of inhibition of thymidine incorporation into DNA by bromodeoxyuridine given simultaneously

Abstract We describe a reproducible method for combining tritiated thymidine ([³H]TdR) autoradiography with immunoperoxidase detection of bromodeoxyuridine (BrdU) in paraffin-embedded tissues. The technique has been used to examine, in mouse tongue epithelium, the inhibition of incorporation into DNA of [³H]TdR by a simultaneous injection of BrdU in the doses that both compounds are likely to be used in cell proliferation studies. The significance that this inhibition has on prolongation of autoradiograph exposure times, to ensure that all cells that incorporate [³H]TdR are scored as positive, in particular the most lightly labelled cells, has been quantified.
The inhibition of uptake into DNA of [³H]TdR from 0.23 to 1.85 MBq (6.25 to 50 μCi) per animal, produced by a simultaneous injection of 2.5 mg BrdU shows a linear, dose-dependent relationship. Provided the injected dose (in μCi per animal) multiplied by the autoradiographic exposure time (in days) is greater than a value of 700, then all cells that are labelled after incorporation of [³H]TdR alone are also labelled after simultaneous double labelling, despite the latter producing a lower average grain count.     

Degradation activity of adhered and suspended Pseudomonas cells cultured on 2,4,6-trichlorophenol, measured by indirect conductimetry

The degradation activity (expressed as specific CO₂ production rates) of adhered and suspended Pseudomonas cells, strains SP1 and SP2, during the degradation of 2,4,6-trichlorophenol (2,4,6-TCP), was compared using indirect conductimetry technique. This technique is defined as the measurement of CO₂ ionization in an alkaline solution and expressed as the negative conductance change values of such solution. The attachment surfaces were porous glass and silicone rubber. The 2,4,6-TCP concentrations ranged from 10 to 500 mg 1⁻¹. Specific respiration rates were determined from CO₂ evolution rates and biomass yields of both suspended and adhered cell cultures. CO₂ evolution rates were determined after conversion of conductance change values into CO₂ produced values. Results indicate that glass-adhered cells reached a higher maximum specific CO₂ evolution rate ( Q _CO2max) than both suspended and silicone rubber-adhered cells. However, suspended cells showed a lower saturation constant ( K_s ) than the adhered cells. These results suggest that depending on support nature the respiration activity of adhered cells could be higher than of suspended cells. Moreover, the indirect conductimetry technique could efficiently be used by measurements of respiration activities of both attached or suspended xenobiotic-degrading micro-organisms.     

Increased biological potency of hexafluorinated analogs of 1,25-dihydroxyvitamin D3 on bovine parathyroid cells

1,25-dihydroxyvitamin D₃ (1,25-(OH)₂D₃) is known to be involved in regulating the proliferation of parathyroid cells and PTH synthesis through reactions involving its nuclear receptor. We evaluated the effects of 1,25-(OH)₂D₃ and its hexafluorinated analog, 26,26,26,27,27,27-hexafluoro-1,25-dihydroxyvitamin D₃ (26,27-F₆-1,25-(OH)₂D₃), on parathyroid cells. The 1,25-(OH)₂D₃ and 26,27-F₆-1,25-(OH)₂D₃ each inhibited [³H]thymidine incorporation and ornithine decarboxylase (ODC) activity, which is important in cell proliferation, in primary cultured bovine parathyroid cells. The inhibitory effect of 26,27-F₆-1,25-(OH)₂D₃ on PTH secretion from parathyroid cells was significantly more potent than that of 1,25-(OH)₂D ₃ between 10⁻¹¹ M and 10⁻⁸ M. Study of 26,27-F₆-1,25-(OH)₂D₃ metabolism in parathyroid cells in vitro elucidated its slower degradation than that of 1,25-(OH)₂D₃. After 48 h of incubation with [1β-³H]26,27-F₆-1,25-(OH)₂D₃, two HPLC peaks, one for [1β-³H]26,27-F₆-1,25-(OH)₂D₃, and a second larger peak for [1β-³H]26,27-F₆-1,23(S),25-(OH)₃D₃, were detected. No metabolites were detected after the same period of incubation with 1,25-(OH)₂[26,27-³H]D₃. We observed that 26,27-F₆-1,23(S),25-(OH)₃D₃ was as potent as 1,25-(OH)₂D₃ in inhibiting the proliferation of parathyroid cells.

Data suggest that the greater biological activity of 26,27-F₆-1,25-(OH)₂D₃ is explained by its slower metabolisms and by the retention of the biological potency of 26,27-F₆-1,25-(OH)₂D₃ even after 23(S)-hydroxylation.     

Recent progress on sperm characterization in flowering plants

The organization, isolation and physiology of the angiosperm male gamete has recently emerged as an area of special interest. Detailed in vivo studies have revealed: (1) that the functional unit of male reproduction is a'male germ unit,'composed of two sperm cells and a physically associated vegetative nucleus; (2) that the two sperm cells are often cytoplasmically dimorphic, and (3) that some sperm cells appear to undergo preferential fertilization, preferentially fusing with either the egg or the proendospermaric central cell. Male gamete isolation has provided enrichments of up to 10⁷ cells ml^–1, with sperm integrity and viability demonstrated by the flunrochromatic reaction and ATP levels. Although results from biochemical and hybridoma antibody characterization are still preliminary, they indicate that sperm cells possess polypeptide expression patterns that are different from those of surrounding cells. These findings suggest the existence of an independent developmental program in the angiosperm male gamete.     

不同供钾水平对平邑甜茶幼苗生长及NO3-吸收利用特性的影响

研究平邑甜茶幼苗NO₃^--N吸收和利用特性对不同供钾水平的响应,旨在明确钾肥对氮肥吸收利用的影响,从而为果园科学施肥提供理论依据.以平邑甜茶幼苗为材料进行砂培试验,设置K₀、K₁、K₂、K₃、K₄、K₅、K₆ 7个钾浓度处理,分别相当于0、2、4、6、8、10、12 mmol·L^-1 K⁺,运用¹⁵N同位素示踪技术和非损伤扫描离子选择电极技术,测定了不同供钾水平下平邑甜茶的氮素吸收和利用情况.结果表明: K₃处理平邑甜茶幼苗根系活力、硝酸还原酶活性以及根系形态指标均显著高于其他处理.与其他处理相比,K₃处理根、茎、叶从肥料中吸收分配到的¹⁵N 量对该器官全氮量的贡献率(Ndff)均达到最高,分别为K₀处理的1.36、1.33和1.47倍.随供钾水平的增加,植株氮素利用率呈现先增高后降低的趋势,且在K₃处理时最大,为23.3%,是K₀处理的3.04倍.非损伤微测技术结果显示,K₃处理时,平邑甜茶根系对NO₃^-有强烈吸收且内流速度达到最大,为19.34 pmol·cm^-2·s^-1;在缺钾(K₀)和高钾(K₆)处理时有明显外排趋势.因此,钾的亏缺或过量均抑制氮素的吸收和利用,适当供钾能够促进幼苗根系生长,增强硝酸还原酶活性,从而促进平邑甜茶对氮素的吸收.     

Autocrine response of Schizosaccharomyces pombe haploid cells to mating pheromones

Abstract The mating response of the fission yeast Schizosaccharomyces pombe is mediated by mating pheromones, M-factor and P-factor, produced by h⁻ and h⁺ cells, respectively. When the M-factor receptor (Map3) was ectopically expressed in h⁻ cells lacking the P-factor receptor (Mam2), they acquired mating competence in response to M-factor which they secreted. The autocrine response to P-factor in h⁺ cells was so weak that mating competence was not acquired, although expression of the pheromone-responsive gene mat1-Pm was detected. These observations support the notion that the intensity of cellular response to mating pheromones is different between h⁻ and h⁺ cells, although downstream pathways of the pheromone receptors are shared by the two mating types.     

Cell cycle dependence of cytotoxicity and clastogenicity induced by treatment of synchronized human diploid fibroblasts with sodium fluoride

To study the cell cycle dependence of cytotoxicity and clastogenicity of sodium fluoride (NaF), synchronized human diploid fibroblasts were treated with NaF during different phases of the cell cycle and analyzed. Exponentially growing cells were synchronized by the following two procedures. (1) The cells were synchronized at G₀/G₁ phase by a period of growth in medium containing 1% serum (low serum medium). (2) The cells were synchronized at the G₁/S boundary by growth in low serum medium, followed by hydroxyurea treatment (Tsutsui et al., 1984a). Synchronized cells were treated with NaF for 3 h during the G₁ phase or G₂ phase, and for each of three 3-h periods during the S phase which lasted 9 h. Cytotoxicity, as determined by a decrease in colony-forming ability, was dependent upon the phase of the cell cycle during which NaF treatment was administered. The highest lethality was induced in when the cultures were treated with NaF during the second or third 3 h of S phase (middle or late S phase, respectively), or G₂ phase. Little lethality was observed in cultures in G₁ phase. Inducibility of chromosome aberrations of the cells following treatment with NaF was also dependent upon the phase of the cell cycle. A significant increase in the incidence of chromosome aberrations was observed only in cultures treated with NaF during early and / or middle S phases of cell cycle. These results suggest that cytotoxicity and clastogenicity of NaF to cultured human diploid fibroblasts are cell cycle dependent, and that the cells in early and middle S phases are more sensitive to the effects.