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51.
Smith LG 《Current opinion in plant biology》1999,2(6):447-453
Plant cells divide in two by constructing a new cell wall (cell plate) between daughter nuclei after mitosis. Golgi-derived vesicles are transported to the equator of a cytoskeletal structure called a phragmoplast, where they fuse together to form the cell plate. Orientation of new cell walls involves actindependent guidance of phragmoplasts and associated cell plates to cortical sites established prior to mitosis. Recent work has provided new insights into how actin filaments and other proteins in the phragmoplast and cell plate contribute to cytokinesis. Newly discovered mutations have identified a variety of genes required for cytokinesis or its spatial regulation. 相似文献
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53.
Summary. Division of the plant cell relies on the preprophase band of microtubules (PPB)-phragmoplast system. Cells of onion (Allium cepa L.) root meristems were rendered binucleate by preventing the consolidation of cell plate formation in telophase with 5mM caffeine. These binucleates developed either a single PPB around one of their two nuclei or two PPBs, one per nucleus, in the prophase of the ensuing mitosis. Prophase cells developing one single PPB were shorter in length (42.3±4.1µm) than those developing 2 PPBs (49.8±4.1µm), and interphase duration was inversely related to cell length. Cells whose length was less than or equal to 42µm, i.e., which had not even reached the mean size of the small binucleates in prophase, were followed throughout mitosis. In metaphase, they always assembled two mitotic spindles (one per nucleus). However, the cells that had assembled a single PPB also developed a single phragmoplast in telophase, leading to polyploidization. As these meristematic cells were not wide enough to accommodate the midzones of both mitotic spindles in any single plane transversal to the cell elongation axis, the spindles tilted until their midzones formed a continuum where the single common phragmoplast assembled. Its position was thereby uncoupled from that of the preceding PPB. Subsequently, the chromosomes from two different half-spindles were included, by a common nuclear envelope, in a single tetraploid nucleus. Finally, the cytokinetic plate segregated the two tetraploid nuclei formed at each side of the phragmoplast into two independent sister cells.Correspondence and reprints: Centro de Investigaciones Biológicas, CSIC, Ramiro de Maeztu 9, 28040 Madrid, Spain. 相似文献
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55.
Plasma membrane-cell wall connections: Roles in mitosis and cytokinesis revealed by plasmolysis ofTradescantia virginiana leaf epidermal cells 总被引:3,自引:0,他引:3
Ann L. Cleary 《Protoplasma》2001,215(1-4):21-34
Summary
Tradescantia virginiana leaf epidermal cells were plasmolysed by sequential treatment with 0.8 M and 0.3 M sucrose. Plasmolysis revealed adhesion of the plasma membrane to the cell wall at sites coinciding with cytoskeletal arrays involved in the polarisation of cells undergoing asymmetric divisions — cortical actin patch — and in the establishment and maintenance of the division site —preprophase band of microtubules and filamentous (F) actin. The majority of cells retained adhesions at the actin patch throughout mitosis. However, only approximately 13% of cells formed or retained attachments at the site of the preprophase band. After the breakdown of the nuclear envelope, plasmolysis had a dramatic effect on spindle orientation, cell plate formation, and the plane of cytokinesis. Spindles were rotated at abnormal angles including tilted into the plane of the epidermis. Cell plates formed but were quickly replaced by vacuole-like intercellular compartments containing no Tinopal-stainable cell wall material. This compartment usually opened to the apoplast at one side, and cytokinesis was completed by the furrow extending across the protoplast. This atypical cytokinesis was facilitated by a phragmoplast containing microtubules and F-actin. Progression of the furrow was unaffected by 25 g of cytochalasin B per ml but inhibited by 10 M oryzalin. Phragmoplasts were contorted and misguided and cytokinesis prolonged, indicating severe disruption to the guidance mechanisms controlling phragmoplast expansion. These results are discussed in terms of cytoskeleton-plasma membrane-cell wall connections that could be important to the localisation of plasma membrane molecules defining the cortical division site and hence providing positional information to the cytokinetic apparatus, and/or for providing an anchor for cytoplasmic F-actin necessary to generate tension on the phragmoplast and facilitate its directed, planar expansion.Abbreviations ADZ
actin-depleted zone
- DIC
differential interference contrast
- GMC
guard mother cell
- MT
microtubule
- PPB
preprophase band
- SMC
subsidiary mother cell
Dedicated to Professor Brian E. S. Gunning on the occasion of his 65th birthday 相似文献
56.
Romano L Scuteri A Gugliotta T Romano P de Luca G Sidoti A Amato A 《Cell biology international》2002,26(5):421-426
This study aimed to show that modifications in intracellular metabolism are implicated in the pathophysiology of diabetes mellitus and essential hypertension. In fact, total magnesium, calcium, sodium and potassium concentrations, measured in the erythrocytes of normotensive, diabetic and hypertensive patients, have given the following results: a lower intracellular potassium concentration in the erythrocytes of diabetic and hypertensive patients than the erythrocytes of normotensive patients and a more elevated sodium, magnesium, calcium concentrations in the erythrocytes of diabetic and hypertensive patients than the normotensive.Because of the importance of Mg2+ and Ca2+ in metabolic enzyme regulation and their interaction with both Hb and band 3 protein, we examined SO4(2-) kinetic influx in the erythrocytes of normotensive, hypertensive and diabetic patients. The kinetic plots showed different profiles over the three groups and the fluxes were found to be 0.024, 0.061 and 0.072 mmol x (l cells x min)(-1) in normotensive, hypertensive and diabetic patients, respectively. We also found that the Vmax and Km of sulphate influx, obtained by Hofstee plots, increased in the erythrocytes of hypertensive and diabetic patients compared with control cells. In contrast, sulphate influx in the erythrocytes of diabetic and hypertensive patients in the presence of Nifedipine, a calcium antagonist, showed no difference either in the rate constants or in the kinetic profiles, compared to the normotensive control subjects. 相似文献
57.
Glidden DV 《Biometrics》2002,58(2):361-368
Multistate event data, in which a single subject is at risk for multiple events, is common in biomedical applications. This article considers nonparametric estimation of the vector of probabilities of state membership at time t. Estimators, derived under the Markov assumption, have been shown (Datta and Satten, 2001, Statistics and Probability Letters 55, 403-411) to be consistent for data that is non-Markov. Inference, however, must take into account possibly non-Markov transitions when constructing confidence bands for event curves. We develop robust confidence bands for these curves, evaluate them via simulation, and illustrate the method on two datasets. 相似文献
58.
59.
Schülke O 《American journal of primatology》2001,55(1):57-63
The demographic structure in the Hanuman langur (Semnopithecus entellus) population of Jodhpur is extreme, in that some single males monopolize harems with, on average, 25 adult females. It has been proposed that extratroop males, which live in all-male bands, inhabit low-quality habitats and suffer from reduced food provisioning and longer daily travel distances. To compare the resulting energetic consequences for harem holders and bachelors, I estimated their gross energy intake and daily energetic expenditures. This analysis revealed no clear-cut differences between the two classes of males in time spent feeding on provisioned food, daily path length, gross energy intake, and energy expenditure. Due to the small sample size and other limitations of the study design, the hypothesis under investigation can not be evaluated conclusively. The preliminary results suggest, however, that energy budgets of harem holders and bachelors do not differ markedly. The importance of direct ecological pressures to males for our understanding of variation in group composition is highlighted. 相似文献
60.
WW781 binds reversibly to red blood cell AE1 and inhibits anion exchange by a two-step mechanism, in which an initial complex (complex 1) is rapidly formed, and then there is a slower equilibration to form a second complex (complex 2) with a lower free energy. According to the ping-pong kinetic model, AE1 can exist in forms with the anion transport site facing either inward or outward, and the transition between these forms is greatly facilitated by binding of a transportable substrate such as Cl(-). Both the rapid initial binding of WW781 and the formation of complex 2 are strongly affected by the conformation of AE1, such that the forms with the transport site facing outward have higher affinity than those with the transport site facing inward. In addition, binding of Cl(-) seems to raise the free energy of complex 2 relative to complex 1, thereby reducing the equilibrium binding affinity, but Cl(-) does not compete directly with WW781. The WW781 binding site, therefore, reveals a part of the AE1 structure that is sensitive to Cl(-) binding and to transport site orientation, in addition to the disulfonic stilbene binding site. The relationship of the inhibitory potency of WW781 under different conditions to the affinities for the different forms of AE1 provides information on the possible asymmetric distributions of unloaded and Cl(-)-loaded transport sites that are consistent with the ping-pong model, and supports the conclusion from flux and nuclear magnetic resonance data that both the unloaded and Cl(-)-loaded sites are very asymmetrically distributed, with far more sites facing the cytoplasm than the outside medium. This asymmetry, together with the ability of WW781 to recruit toward the forms with outward-facing sites, implies that WW781 may be useful for changing the conformation of AE1 in studies of structure-function relationships. 相似文献