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81.
Indirect immunofluorescence microscopy has been used to investigate the ultraviolet (UV) radiation induced disruption of the organization of microfilaments, keratin intermediate filaments, and microtubules in cultured human epidermal keratinocytes. Following irradiation, concurrent changes in the organization of the three major cytoskeletal components were observed in cells incubated under low Ca2+ (0.15 mM) conditions. UV irradiation induced a dose-dependent condensation of keratin filaments into the perinuclear region. This collapse of the keratin network was accompanied by the reorganization of microfilaments into rings and a restricted distribution of microtubules, responses normally elicited by exposure to high Ca2+ (1.05 mM) medium. The UV induced alteration of the keratin network appears to disrupt the interactions between keratin and actin, permitting the reorganization of actin filaments in the absence of Ca2+ stimulation. In addition to the perinuclear condensation of keratin filaments, UV irradiation inhibits the Ca2+ induced formation of keratin alignments at the membrane of apposed cells if UV treatment precedes exposure to high Ca2+ medium. Incubation of keratinocytes in high Ca2+ medium for 24 hours prior to irradiation results in the stabilization of membrane associated keratin alignments and a reduced susceptibility of cytoplasmic keratin filaments to UV induced disruption. Unlike results from investigations with isogenic skin fibroblasts, no UV induced disassembly of microtubules was discernible in irradiated human keratinocytes.  相似文献   
82.
Terminal meristems of Pisum sativum (garden pea) transit from vegetative to inflorescence development, and begin producing floral axillary meristems. Determination for inflorescence development was assessed by culturing excised buds and meristems. The first node of floral initiation (NFI) for bud expiants developing in culture and for adventitious shoots forming on cultured meristems was compared with the NFI of intact control buds. When terminal buds having eight leaf primordia were excised from plants of different ages (i.e., number of unfolded leaves) and cultured on 6-benzylaminopurine and kinetin-supplemented medium, the NFI was a function of the age of the source plant. By age 3, all terminal buds were determined for inflorescence development. Determination occurred at least eight nodes before the first axillary flower was initiated. Thus, the axillary meristems contributing to the inflorescence had not formed at the time the bud was explanted. Similar results were obtained for cultured axillary buds. In addition, meristems excised without leaf primordia from axillary buds three nodes above the cotyledons of age-3 plants gave rise to adventitious buds with an NFI of 8.3 ±0.3 nodes. In contrast seed-derived plants had an NFI of 16.5 ±0.2. Thus cells within the meristem were determined for inflorescence development. These findings indicate that determination for inflorescence development in P. sativum is a stable developmental state, separable from determination for flower development, and occurring prior to initiation of the inflorescence at the level of meristems.  相似文献   
83.
In order to estimate photosynthetic and respiratory rates in illuminated photoautotrophic cells of carnation (Dianthus caryophyllus L.), simultaneous measurements of CO2 and O2 gas exchange were performed using 18O2, 13CO2 and a mass-spectrometry technique. This method allowed the determination, and thus the comparison, of unidirectional fluxes of O2 and CO2. In optimum photosynthetic conditions (i.e. in the presence of high light and a saturating level of CO2), the rate of CO2 influx represented 75±5% of the rate of gross O2 evolution. After a dark-to-light transition, the rate of CO2 efflux was inhibited by 50% whereas the O2-uptake rate was little affected. The effect of a recycling of respiratory CO2 through photosynthesis on the exchange of CO2 gas was investigated using a mathematical model. The confliction of the experimental data with the simulated gas-exchange rates strongly supported the view that CO2 recycling was a minor event in these cells and could not be responsible for the observed inhibition of CO2 efflux. On the basis of this assumption it was concluded that illumination of carnation cells resulted in a decrease of substrate decarboxylations, and that CO2 efflux and O2 uptake were not as tightly coupled in the light as in the dark. Furthermore, it could be calculated from the rate of gross photosynthesis that the chloroplastic electron-transport chain produced enough ATP in the light to account for the measured CO2-uptake rate without involving cyclic transfer of electrons around PS I or mitochondrial supplementation.Abbreviations Chl chlorophyll - Kd permeability coefficient The authors thank Drs A. Vermeglio and P. Thibault, Dépt. de Biologie, CEN-Cadarache, St. Paul Lez Durance, France, for helpful discussions.  相似文献   
84.
Summary In the hepatitis B surface antigen (HBsAg)-producing recombinant yeast culture medium, the supply of Bacto-yeast nitrogen base without amino acids was found to be inadequate due to the lack of the several kinds of vitamins and trace elements. When the culture medium for this recombinant yeast was supplemented with sufficient vitamins and trace elements, its growth, HBsAg production and the stability of plasmid were improved.  相似文献   
85.
Summary Female gametangia of the normal bisexual Allomyces species are richer in fluorescently probed (FITC) actin, independent of their apical or subapical positioning during differentiation on the fertile hyphae. The anti-actin, cytochalasin D, can selectively suppress male differentiation in both species.  相似文献   
86.
Of the total number of breast cancers approx. 30-50% are hormone-dependent and estradiol is one of the main factors of cancerization. Consequently, the control of this hormone inside the cancer cell is of capital importance because it is well established that the inhibition of estradiol biosynthesis can have a positive effect on the evolution of the disease. The blockage of estradiol can be obtained by the action of anti-aromatases, anti-sulfatases, the control of the 17 beta-hydroxysteroid dehydrogenase activity or by the stimulation of the sulfotransferase which converted the estrogens in their sulfates. In breast cancer tissue estrone sulfate is quantitatively the most important source of estradiol. In the intact cell, estrone sulfatase activity is very intense in the hormone-dependent cell lines (e.g. MCF-7, T-47D) but very small activity is observed in the hormone-independent (e.g. MDA-MB-231, MDA-MB-436) cell lines. However, this activity became very strong after homogenization in the hormone-independent cells, suggesting the presence of repressive factor(s) for this enzyme or its sequestering in an inactive form, in the intact cells of these cell lines. In a series of previous studies it was found that in hormone-dependent cell lines different anti-estrogens: tamoxifen and derivatives, ICI 164,384, very significantly decrease the estradiol concentration originated from estrone sulfate, and recently it was observed that Decapeptyl (D-Trp6-gonadotropin-releasing hormone) in the presence of heparin can also decrease the conversion of estrone sulfate into estradiol. No significant effect was obtained in the presence of heparin or Decapeptyl alone. The estrone sulfatase activity can be inhibited by progesterone, the progestagen R-5020, and testosterone. In another series of recent studies the presence of very strong estrogen sulfotransferase activity has been shown in one breast cancer cell line, the MDA-MB-468. We can conclude that: (1) the control of estradiol concentration can be carried out in the breast cancer tissue itself; (2) estrone sulfate can play an important role in the bioavailability of estradiol in the breast cancer cell; and (3) as is the case for the aromatase, the control of: the estrogen sulfatase, estrogen sulfotransferase, and 17 beta-hydroxysteroid dehydrogenase can be new targets for therapeutic applications in breast cancer.  相似文献   
87.
黑叶猴和菲氏叶猴颅骨的比较研究   总被引:1,自引:0,他引:1  
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88.
对武汉东湖三个定点观测站和潜江市一深水机井中异养细菌群落的种群组成、对不同基质的反应、菌株和群落的生理特征和活力水平等方面比较研究结果表明:环境差异较小的东湖Ⅰ、Ⅱ、Ⅲ站异养细菌群落间的差异亦较小,具有类似的结构特征和生理活力水平,对特定基质表现了相似的作用模式;地下水中的异养细菌群落在上述几方面均显示了明显的差别。此外,在异养细菌群落结构和功能研究方法上亦是有益的探讨。  相似文献   
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