A phylogenetic analysis of the SSU rRNA from members of the Plasmodiophorida and Phagomyxida

The Plasmodiophorida and Phagomyxida are orders of zoosporic eukaryotes of uncertain phylogenetic affinities. We have obtained ribosomal DNA sequence information from several species in these groups. Phylogenetic analyses of these sequences have confirmed that they form a monophyletic grouping that clusters most closely with a rhizopod assemblage consisting of sarcomonads and chlorarachneans. The Phagomyxida sequences appear distant enough from those of the Plasmodiophorida to justify a separate order. The relationships between the Plasmodiophorida remain unclear, with species from the same genus showing significant degrees of divergence.

Bacillus thuringiensis and its pesticidal crystal proteins

During the past decade the pesticidal bacterium Bacillus thuringiensis has been the subject of intensive research. These efforts have yielded considerable data about the complex relationships between the structure, mechanism of action, and genetics of the organism's pesticidal crystal proteins, and a coherent picture of these relationships is beginning to emerge. Other studies have focused on the ecological role of the B. thuringiensis crystal proteins, their performance in agricultural and other natural settings, and the evolution of resistance mechanisms in target pests. Armed with this knowledge base and with the tools of modern biotechnology, researchers are now reporting promising results in engineering more-useful toxins and formulations, in creating transgenic plants that express pesticidal activity, and in constructing integrated management strategies to insure that these products are utilized with maximum efficiency and benefit.

Revision of the nomenclature for the Bacillus thuringiensis pesticidal crystal proteins

The crystal proteins of Bacillus thuringiensis have been extensively studied because of their pesticidal properties and their high natural levels of production. The increasingly rapid characterization of new crystal protein genes, triggered by an effort to discover proteins with new pesticidal properties, has resulted in a variety of sequences and activities that no longer fit the original nomenclature system proposed in 1989. Bacillus thuringiensis pesticidal crystal protein (Cry and Cyt) nomenclature was initially based on insecticidal activity for the primary ranking criterion. Many exceptions to this systematic arrangement have become apparent, however, making the nomenclature system inconsistent. Additionally, the original nomenclature, with four activity-based primary ranks for 13 genes, did not anticipate the current 73 holotype sequences that form many more than the original four subgroups. A new nomenclature, based on hierarchical clustering using amino acid sequence identity, is proposed. Roman numerals have been exchanged for Arabic numerals in the primary rank (e.g., Cry1Aa) to better accommodate the large number of expected new sequences. In this proposal, 133 crystal proteins comprising 24 primary ranks are systematically arranged.

Micromanipulation of statoliths in gravity-sensing Chara rhizoids by optical tweezers

Infrared laser traps (optical tweezers) were used to micromanipulate statoliths in gravity-sensing rhizoids of the green alga Chara vulgaris Vail. We were able to hold and move statoliths with high accuracy and to observe directly the effects of statolith position on cell growth in horizontally positioned rhizoids. The first step in gravitropism, namely the physical action of gravity on statoliths, can be simulated by optical tweezers. The direct laser microirradiation of the rhizoid apex did not cause any visible damage to the cells. Through lateral positioning of statoliths a differential growth of the opposite flank of the cell wall could be induced, corresponding to bending growth in gravitropism. The acropetal displacement of the statolith complex into the extreme apex of the rhizoid caused a temporary decrease in cell growth rate. The rhizoids regained normal growth after remigration of the statoliths to their initial position 10-30 micrometers basal to the rhizoid apex. During basipetal displacement of statoliths, cell growth continued and the statoliths remigrated towards the rhizoid tip after release from the optical trap. The resistance to statolith displacement increased towards the nucleus. The basipetal displacement of the whole complex of statoliths for a long distance (>100 micrometers) caused an increase in cell diameter and a subsequent regaining of normal growth after the statoliths reappeared in the rhizoid apex. We conclude that the statolith displacement interferes with the mechanism of tip growth, i.e. with the transport of Golgi vesicles, either directly by mechanically blocking their flow and/or, indirectly, by disturbing the actomyosin system. In the presence of the actin inhibitor cytochalasin B the optical forces required for acropetal and basipetal displacement of statoliths were significantly reduced to a similar level. The lateral displacement of statoliths was not changed by cytochalasin B. The results indicate: (i) the viscous resistance to optical displacement of statoliths depend mainly on actin, (ii) the lateral displacement of statoliths is not impeded by actin filaments, (iii) the axially directed actin-mediated forces against optical displacement of statoliths (for a distance of 10 micrometers) are stronger in the basipetal than in the acropetal direction, (iv) the forces acting on single statoliths by axially oriented actin filaments are estimated to be in the range of 11-110 pN for acropetal and of 18-180 pN for basipetal statolith displacements.

Mobile and immobile endoplasmic reticulum in onion bulb epidermis cells: short- and long-term observations with a confocal laser scanning microscope

The endoplasmic reticulum (ER) of onion bulb scale epidermis cells consists of long, tubular strands lying deep in the cytoplasm which move quickly and a less mobile peripheral network of tubules and cisternae that change in position, shape and size but that also have immobile, fixed, sites (IFSs). IFSs occur in junctions, at vertexes and at blind endings of tubules as well as at the edges and the surface of cisternae. They are regularly arranged in helicoidal rows and may be knot- or ring-like in structure. They become enlarged by treatment with oryzalin but not with colchicine. They persist for long times (for more than 30 min); together with pulling forces, the surface tension and other factors, they determine the configuration and motion of the peripheral network. New polygons of the network are mainly formed by the development of new tubules that become joined with other parts of the network. Polygons disappear by contraction and fusion of tubules. The inner, rapidly moving ER tubules remain connected with the peripheral network over longer distances by sliding junctions. Cytochalasin D causes an accumulation of the ER into patches, a fusion of tubules into cisternae and changes in shape, which indicate the loss of pulling forces. In contrast to animal cells (but like the movement of the inner tubular strands), the latter is dependent upon the actomyosin system; microtubules are not involved. Despite the differences in the organizing components, the peripheral ER in onion bulb scale epidermis cells and that of the borders of cultured animal cells are similar in morphology and motility.

Effects of nifedipine, verapamil, and diltiazem on tip growth inFunaria hygrometrica

Protonemata ofFunaria hygrometrica Sibth. were treated with nifedipine, verapamil, or diltiazem. Responses to each of the drugs were, on the one hand, reduction of growth rate and tip cell length and, on the other hand, formation of apical swellings in caulonema tip cells and of anomalously oriented separation walls between main filaments and young side branches. The first effect is regarded as a more general expression of inhibition while the second complex of effects is attributed to perturbations in directed vesicle transport. Replacement of drug-containing media by normal Knop agar demonstrated the reversibility of inhibitor action: growth parameters were comparable to those of control protonemata within a few hours. A fast reaction, the formation of subapical vacoules, occurred within minutes of drug application and was only observed with verapamil and diltiazem. In connection with this process, rapid migrations of chloroplasts took place, but examination of the microtubule cytoskeleton in such cells by indirect immunofluorescence with a monoclonal antibody against tubulin showed an intact microtubule network. callose deposits in tip cells treated with verapamil. They were polarly distributed and started to appear in cell apices about 2h after the beginning of verapamil application. Two mechanisms of action for the tested inhibitors are discussed: (i) perturbations of membrane permeability by interference with one or more of the cell's Ca(2+)-transport systems, and (ii) a more indirect mechanism affecting vesicle transport via the microfilament system.

Correlation between protonema morphogenesis and the development of the microtubule system in Funaria spore germination under normal conditions and at high auxin concentrations: an immunofluorescence study

Ungerminated spores of Funaria do not contain distinct microtubules but show diffuse antitubulin antibody fluorescence. The microtubules arise when, 24–48 h after sowing, the spores are swollen and the first germ tube begins to protrude. Initially, diffuse fluorescence and microtubules are concentrated around the nucleus. Treatment with auxin at high concentrations (5 × 10−5 – 10−4 M) retards germination and cell division. Like antimicrotubule agents, such as colchicine and chloroisopropyl-N-phenylcarbamate, high auxin concentrations affect the formation of microtubules; either short, irregularly shaped microtubules and fluorescent spots arise, or there is no evidence of microtubules. The auxin effects on growth and microtubules can be reversed in less than 1 day. There is a correlation between the formation of the microtubule system and cell morphogenesis.

Reorganization of the endoplasmic reticulum in epidermal cells of onion bulb scales after cold stress: Involvement of cytoskeletal elements

In the epidermal cells of onion (Allium cepa L.) bulb scales the endoplasmic reticulum (ER) can be subdivided into three domains: a peripheral tubular network, cisternae, and long tubular strands. The latter are the form in which the ER is moved in onion cells. During cold treatment the arrangement of the three domains changes drastically. The cisternae and long tubular strands disintegrate into short ER tubules which show rapid agitational motion. Long-distance movement is inhibited. The peripheral tubular ER network is presumably retained during cold treatment. Rewarming of previously chilled bulb scales initiates the reorganization of the ER into the three domains. The ER is partly relocated during recovery from cold treatment. Redistribution and reorganization of the ER is not affected by the microtubule-destabilizing herbicides oryzalin and trifluralin (5 μM). Cytochalasin D (2μM), however, inhibits not only the relocation of ER material, as is evident by the absence of long tubular ER strands, but also the movement of other cell organelles. The latter cluster on top of the cisternae in a manner which is characteristic of treatment with the actin-filament inhibitor. The array of actin filaments is similar in unstressed, cold-treated cells, and cells which recover from low temperatures in the presence of oryzalin or tap water alone. In the presence of cytochalasin D the actin filaments are severely fragmented. The results indicate that low temperatures most likely influence either the interaction of the force-generating system, probably myosin, with actin filaments, or the force-generating mechanism of the actomyosin-driven intracellular movement, but do not affect actin-filament integrity.

The cytoskeleton of Cobaea seed hairs: : Patterning during cell-wall differentiation

The cell wall of Cobaea scandens seed hairs developed in a characteristic sequence, with the deposition of a cellulose thread onto a pectic swelling layer was the final event. The cellulose thread was intracellularly accompanied by a band of 10-18 microtubules. During the formation of the swelling layer the microtubules were homogeneously distributed; they ran circumferentially normal to the cell axis. When cellulose-thread formation started, the microtubules became arranged in a helical band. The density of the microtubules varied during the different phases of development. The highest density was observed before cellulosethread formation and ranged from 6-15 μm·μm(-2). The length of the microtubules, 20-30 μm, was determined by direct measurements, as well as estimated from the total microtubular length in a given area and the counted free ends. With the indirect immunofluorescence technique the microtubules of the band stained inhomogeneously. Those which were located at the edges of the band fluoresced more intensely than those of the central part. Attempts to visualize actin filaments in the hair cells with rhodaminyl-conjugated phalloidin resulted in a homogeneous staining of the area of the microtubular band, indicating that actin filaments may be present in this region. Though, in thin sections and dry-cleaved cells, filamentous structures were observed between the microtubules, caution is expressed that the observed fluorescence was, indeed, due to actin filaments. The role of the filamentous structures is discussed with respect to formation and maintenance of the microtubular band. Microtubules apparently did not cross coated pits which were visualized in the plasma membrane through the dry-cleaving technique.

Chemotaxis and appetence of Paulsenella sp. (Dinophyta), an ectoparasite of the marine diatom Streptotheca thamesis Shrubsole

The parasitic dinophyte, Paulsenella sp., is attracted chemotactically by its host, the centric diatom Streptotheca thamesis. Seemingly rather short-lived components of the diatom mucilage are involved in the process. These components are presumably secreted by the Golgi apparatus and pass the thecal slit between epi-and hypocingulum. Experiments with concanavalin A indicate that glucose and-or mannose are constituents of the effective component, which is obviously not produced by egg cells, sperm cells and auxozygotes, since these stages do not attract the parasite. Plasmolysis inhibits secretion of the effective component. The readiness of the parasite to attack a host cell (its appetence) is light dependent: it is low in the dark period and increases after the beginning of the light period in cultures with a 14 h light/10 h dark regime. Endogenous rhythms of the parasite do not seem to be involved. In contrast, the attractiveness of the host is not influenced by the illumination.

The plasma membrane of the Funaria caulonema tip cell: morphology and distribution of particle rosettes, and the kinetics of cellulose synthesis

Freeze-fracturing of Funaria hygrometrica caulonema cells leads to a cleavage within the plasma membrane. The extraplasmatic and the plasmatic fracture faces differ in their particle density. The plasmatic fracture face in caulonema tip cells or in tip cells of side branches, but never in other caulonema cells, is further characterized by the occurrence of particle rosettes. The highest density of rosettes is found at the cell apex but decreases steeply toward the cell base. The shape of the rosettes varies remarkably; 20% of them are found in an incomplete, presumably disintegrating or aggregating state. The complete rosette has a diameter of about 25 nm and consists of five to six particles. The size of the single particles varies between 4 nm to 10 nm. The rosettes are thought to posses cellulose-synthase activity. It is assumed that one rosette produces one elementary fibril; rough calculations, considering the number of rosettes and the estimated amount of cellulose produced in the tip region, indicate that an elementary fibrillar length of 900 nm is formed in 1 min by one rosette. The consequence of the kinetics on the life-time of the rosettes and the cellulose-synthase activity are discussed.

Evolution of succulent Euphorbia,/i> as interpreted from latex composition. ACTA ACUST UNITED AC 1983. [DOI: 10.4102/abc.v14i3/4.1254]

The morphology of starch grains and the gas-liquid chromatographic profile of triterpenes derived from latex of the nonarticulated laticifer of succulent African  Euphorbia were examined for their applicability to interpret phylogenetic relationships of this genus. Several trends in starch grain morphology and triterpene composition were evident in the 38 examined taxa. Rod shaped grains, interpreted to be conservative, occurred in only a few taxa in several dwarf groups. Grains of osteoid shape prevailed in most taxa. Highly osteoid grains possessing lobed ends represented the most complex form and were present in some taxa endemic to Madagascar. Triterpene profiles which contained from 2 to 14 or more compounds were derived from all taxa. Each taxon possessed a characteristic profile, or identifying fingerprint. The composition of the profile differed quantitatively and qualitatively among taxa. Taxa with few triterpenes, tentatively interpreted as primitive, occurred in dwarf forms, whereas Madagascan taxa tended to possess high numbers of triterpenes reflective of specialization. This study supports the interpretation that laticifer starch grain morphology and triterpene composition, both gene mediated stable markers, can be employed to determine and correlate phylogenetic relationships between taxa of this complex genus.

Polarity and growth of caulonema tip cells of the moss Funaria hygrometrica

In the caulonema tip cells of Funaria hygrometrica, chloroplasts, mitochondria, and dictyosomes have differences in structure which are determined by cell polarity. In contrast to the slowly growing chloronema tip cells the apical cell of the caulonema contains a tip body. Colchicine stops tip growth; it causes the formation of subapical cell protrusions, redistribution of the plastids, and a loss of their polar differentiation. Cytochalasin B inhibits growth and affects the position of cell organelles. After treatment with ionophore A23 187, growth is slower and shorter and wider cells are formed. D2O causes a transient reversion of organelle distribution but premitotic nuclei are not dislocated. In some tip cells the reversion of polarity persists; they continue to grow with a new tip at their base. During centrifugation, colchicine has only a slight influence on the stability of organelle anchorage. The former polar organization of most cells is restored within a few hours after centrifugation, and the cells resume normal growth. In premitotic cells the nucleus and other organelles cannot be retransported, they often continue to grow with reversed polarity. Colchicine retards the redistribution of organelles generally and increases the number of cells that form a basal outgrowth. The interrelationship between the peripheral cytoplasm and the nucleus and the role of microtubules in maintaining and reestablishing cell polarity are discussed.

Development and ultrastructure of the marine, parasitic oomycete, Lagenisma coscinodisci (Lagenidiales): sexual reproduction

Fine structural details of antheridia and oogonia, of cytogamy, plasmogamy, and karyogamy, and finally of the development of the oospore are described. Sexually determined zoospores (most probably zoomeiospores) resemble vegetative primary zoospores (zoomitospores). They form gametangia (antheridia or oogonia) which are similar to vegetative primary cysts. An antheridium germinates with a fertilization tube which penetrates the oogonium. As seen in abnormal cell fusions, the tip of the fertilization tube opens only within an oogonium; presumably, its wall is disintegrated by the latter. Before plasmogamy, both plasmalemmata are closely appressed. The fused protoplasts move into a short zygotial hypha which protudes from the oogonium. The thick-walled oospore is formed herein. It includes nearly all of the cytoplasm of the gametangia. Karyogamy takes place within the developing oospore. It is initiated by an interdigitation of microtubules radiating from the centrioles and by a close association of the latter. The observations are compared with those on other developmental stages of Lagenisma and with those on gametangia and oospores of other Oomycetes.

Chitinous fibrils in the lorica of the flagellate chrysophyte Poteriochromonas stipitata (syn. Ochromonas malhamensis)

Ordered microfibrils are formed on the membrane of the cytoplasmic tail of the alga Poteriochromonas after attachment to a substrate. The ultrastructure of native and extracted stalk fibrils was studied with electron microscope methods. In addition, the structural polysaccharide was characterized by hydrolyses, separation of the monomers by thin-layer chromatography, gas-liquid chromatography and amino acid analysis, and by X-ray diffraction. The alkali-resistant fibrils yielded mostly glucosamine upon extensive hydrolysis, and showed X-ray diffraction patterns similar to those of fugal chitin. It is concluded that the resistant core of the fibrils is chitinous.