摘要:

A brief review of the role of contractile proteins in dynamic changes in the cytoskeletons of motile cells is followed by a more detailed account of cytoskeletal ultrastructure in the motility of the giant amoeba,Chaos carolinensisand of human blood platelets.

ISSN:0008-4026    

DOI:10.1139/b80-095

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Our work on actin and myosin fromPhysarumis briefly reviewed, and the physicochemical properties of these proteins are compared with those of the corresponding proteins obtained from rabbit striated muscle. In this article both similarities and differences between these preparations are emphasized in order to characterize thePhysarumactomyosin system. Some properties ofPhysarumactinin, a regulatory protein of actin polymerization, are also reported. Finally, the assembly and disassembly of F-actin filaments in the reversible superprecipitationof Physarumactomyosin are demonstrated. The mechanism of generation of the motive force for protoplasmic streaming in plasmodium is discussed in the light of these findings.

ISSN:0008-4026    

DOI:10.1139/b80-096

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Three or four parallel fibrils of ca. 0.1 μm in width attached to each file of chloroplasts in intact internodal cells generate the motive force for cytoplasmic streaming. Experimental evidence for this conclusion is drawn from experiments in which fibrillar motion and streaming are interrupted by centrifugation, microbeam irradiation, and electrical stimulation. The role of Pb2+in preventing cessation of cytoplasmic streaming after electrical stimulation is interpreted in terms of localized changes in viscosity of the cytoplasm.

ISSN:0008-4026    

DOI:10.1139/b80-097

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The occurrence of actin in plant cells is described. Evidence is summarized in favour of the view that its role in animal cells may extend beyond force production for conspicuous motile events. Actin's role in cytoplasmic streaming in plants is then discussed and the possibility of its involvement in other aspects of plant cell physiology is raised.

ISSN:0008-4026    

DOI:10.1139/b80-098

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Cytochalasin B (CB), thought to disaggregate F-actin in animal cells, and phalloidin (Phal), known to stabilize F-actinin vivoandin vitro, have nearly identical effects on cotyledon epidermal cells ofAllium cepa. Both drugs rapidly induce cessation of streaming and both, by preventing normal telophase reorientation movement, lead to abnormal division planes in dividing guard mother cells. Neither, however, prevents normal microtubule deposition, wall thickening, and cellulose orientation during guard cell differentiation. Furthermore, both drugs have no effect on spindle formation and anaphase chromosome motion. Examination ofNitellaandCharacells, in which streaming had been stopped by either agent, shows that microfilament cables are still present. With both drugs, the minimum effective concentrations were routinely used (CB, 2 μM; Phal, 100–200 μM). Our results are discussed in terms of the mode of action of these drugs and their possible role in host-fungus interactions. Implications for the mechanisms underlying cell plate alignment, cellulose orientation, and cytoplasmic streaming are discussed.

ISSN:0008-4026    

DOI:10.1139/b80-099

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Plasmodesmata were recorded in vivo inNitella furcatausing polarization and differential interference-contrast light microscopy, techniques that could prove useful for further physiological experimentation on intercellular transport in characean cells.Freeze-fractured, deep-etch replicasof Nitellaendoplasm were prepared without the use of cryoprotective agents. The endoplasm, in which rapid cytoplasmic streaming occurs, contains intricate three-dimensional networks of filaments of which two prominent size classes are characterized: 7- to 8-nm putative actin filaments and 4- to 5-nm putative myosin filaments. It is quite likely that the putative actin filaments are components of the endoplasmic filaments, and that these filaments interacting with the 4- to 5-nm filaments produce the motive force generating the observed cytoplasmic streaming.

ISSN:0008-4026    

DOI:10.1139/b80-100

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Proteins exhibiting all of the basic structural and biochemical characteristics of actin and myosin have been isolated from the parenchymal cells of the fruit of the tomato,Lycopersicon esculentum. Crude cytoplasmic extracts of these cells contain filaments that can be decorated by rabbit skeletal muscle myosin subfragment-1 (S-1). Polymerized tomato actin activates the Mg2+–ATPase of both skeletal and tomato myosin at physiological ionic strength. Tomato actin comigrates with skeletal actin on sodium dodecyl sulfate polyacrylamide gels (SDS-PAGE) indicating an apparent molecular weight of 45 000. High ionic strength extracts of tomato contain a myosin whose ATPase activity in 0.5 MKCl is maximal in the presence of K+-ethylenediaminetetraacetic acid (K+-EDTA) and is inhibited by Mg2+. Tomato myosin interacts with skeletal F-actin to form an actomyosin complex that can be dissociated by ATP. At low ionic strength the Mg2+–ATPase of the myosin can be activated by actin.

ISSN:0008-4026    

DOI:10.1139/b80-101

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

The heterogeneous group of proteins occurring in the exudate of cut phloem tissue will be termed phloem proteins. Their molecular weights range from less than 30 000 to over 100 000. The protein pattern is a species-specific constant. Depending on the plant species the bulk of phloem proteins is either basic or acidic. InCucurbita maximaup to 40% of the total phloem proteins are basic proteins with a molecular weight of 116 000; it shows G–F transition properties in vitro and represents the so-called P-protein in the sieve tubes of angiosperms. Depending on the stage of cell differentiation the P-protein shows various conformational changesin situ: amorphous, filamentous tubular, and paracrystalline structures are described. P-protein differs from actin- or tubulinlike proteins with regard to their molecular weight and most biochemical characteristics. The main discrepancy is the failure to bind either heavy meromyosin or any nucleotides and colchicine. No structural evidence exists for cytoplasmic streaming in mature sieve tubes based on an actin–myosin system. The function of P-protein is still questionable; sieve pore plugging after wounding, sites of enzymatic activity, and surface interaction are discussed.

ISSN:0008-4026    

DOI:10.1139/b80-102

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Microfilaments 50–70 Å (Å = 0.1 nm) in diameter are commonly found in vascular tissue of elongating roots and stems of many plants. Such microfilaments occur in bundles in peripheral regions of elongating or differentiating vascular cells, and are usually oriented parallel to the longitudinal axis of the cells. Although the longest microfilament bundle we have measured is about 15 μm, we suspect that the bundles are at least as long as the cells that contain them. The bundles are 0.1–0.4 μm in width and are often in apparent contact with organelles, but there is no definite indication of their being anchored to plasmalemma or any organelle. The microfilaments are comparable in size and morphology to actin filaments. The distribution of microfilament bundles in the vascular tissue of various plants and the possible function of the bundles is discussed.

ISSN:0008-4026    

DOI:10.1139/b80-103

出版商:NRC Research Press    

年代:1980

数据来源: NRC

摘要:

Experiments on the movement of14C-assimilates through dissected vascular bundles ofPelargonium zonaleare reviewed. Potassium cyanide (KCN) applied to the central bundle causes localized, reversible blockage of transport. Both antimycin and atractylate, but not ouabain inhibit the movement of metabolites through the phloem. The proton ionophore, CCCP completely suppresses translocation at 10−7 M, however, cell membranes are damaged. Valinomycin applied to cut bundles causes serious disturbances in carbon metabolism as shown by the increased label in sugar phosphates. Cytochalasin B does not affect translocation. Limitations on conclusions drawn from inhibitor studies are discussed.

ISSN:0008-4026    

DOI:10.1139/b80-104

出版商:NRC Research Press    

年代:1980

数据来源: NRC