Showing papers in "Protoplasma in 1991"
TL;DR: The resistance of poplar cultivars to mistletoe was dependent on the production of defensive mechanisms against the pathogen, and these reactions were weaker in the FPL cultivar than in the VER one.
Abstract: Flavonoid compounds were studied in healthy and parasitized poplar branches following mistletoe (Viscum album L.) attack. Two poplar cultivars showing different degrees of resistance to mistletoe: sensitive “Fritzi Pauley” (FPL) and resistant “Vereecken” (VER) were used. Flavonoids were detected and localized using histofluorescence after treating frozen sections with two specific reagents. Total amounts of flavonoids were determined spectrophotometrically. Defence mechanisms were induced during penetration of the primary haustorium. They consisted of inner periderm development and flavonoid accumulation. These reactions were weaker in the FPL cultivar than in the VER one. In the latter, growth of the primary haustorium and the establishment of direct connections between the living host cells and parasite failed. The resistance of poplar cultivars to mistletoe was dependent on the production of defensive mechanisms against the pathogen.
121 citations
TL;DR: Examination of the characters of the flagellar apparatus and its associated cytoskeleton is examined to obtain clues used for phylogenetic consideration on the three cited groups of flageLLates.
Abstract: The hypothesis that protists without mitochondria, the so-called Archezoa of Cavalier-Smith, are primitive has received some support from rRNA sequence studies on Microsporidia and Diplomonadida. In spite of the lack of mitochondria the archezoan groups of protists show considerable differences in their organization: mastigont and cytoskeletal system, mitosis, Golgi apparatus, hydrogenosomes. This paper examines the characters of the flagellar apparatus and its associated cytoskeleton to obtain clues used for phylogenetic consideration on the three cited groups of flagellates. Archamoebae of the Pelobiontida order comprising families such as Pelomyxidae and Mastigamoebidae share common features: a rudimentary mastigont system composed of only one basal body giving rise to a poorly motile flagellum and a basal body associated microtubular cone capping the nucleus. No Golgi apparatus has been detected.
115 citations
TL;DR: In this paper, the formation of cell connections at the graft interface of 5-day old in vitro heterografts of Vicia faba onHelianthus annuus was studied.
Abstract: De novo formation of cytoplasmic cell connections are studied at the graft interface of 5 day old in vitro heterografts ofVicia faba onHelianthus annuus. Continuous and half plasmodesmata, both branched and unbranched, are described at various stages of development in non-division walls between unlike and like dedifferentiated callus cells. In apical portions of protruding callus cells and in the contact zone between opposing cells extremely thin wall parts with a striking ER/plasmalemma contact are observed. During subsequent thickening of the modified wall parts cytoplasmic strands enclosing constricted ER cisternae are entrapped within the newly deposited wall material. These cytoplasmic strands represent half plasmodesmata which—in case of fusion with corresponding structures of adjoining cells across the loosened wall matrix — form continuous cell connections. Golgi vesicles secreting wall material are involved in the process of forming half and continuous plasmodesmata, thus following the same mechanism of plasmodesmata development as described for isolated protoplasts in cell cultures. The findings suggest the existence of a unifying mechanism of secondary formation of plasmodesmata showing far-reaching similarities with the establishment of primary cell connections.
104 citations
TL;DR: In this article, the cells of those proembryoids just emerging through the epidermis are seen to be linked by a fibrillar network, the nature of which is discussed.
Abstract: Leaves from 2-month-old in vitro grown plantlets of a clone ofCichorium placed in agitated liquid induction medium at 35°C in the dark produce embryoids after 5 days of culture, without synchronization. Vascular sheath parenchyma cells react first, but every mesophyll cell is potentially embryogenic. Single cells show an early patchy callosic wall and undergo dedifferentiation. With SEM the cells of those proembryoids just emerging through the epidermis are seen to be linked by a fibrillar network, the nature of which is discussed. Four FITC-labelled lectins were tested; only DBA shows embryogenic specificity.
100 citations
TL;DR: A system for numbering algal flagella and basal bodies, which is based on developmental studies, is discussed along with the various means by which the flagellar/basal body developmental cycle can be determined.
Abstract: Recent evidence has shown that algal cells acquire different flagella and a heterogeneous basal apparatus through the prolonged development of these structures over more than one cell cycle. A system for numbering algal flagella and basal bodies, which is based on developmental studies, is discussed along with the various means by which the flagellar/basal body developmental cycle can be determined. We review the information now available on development of the separate components of the flagellar apparatus — this comes particulary from the Chlorophyta and the Chromophyta— and attempt to elucidate any information which may help in phylogenetic comparisons. New data is provided on developmental changes in the cartwheel part of the basal body and basal bodyassociated connecting fibrils in green algae.
91 citations
TL;DR: Flow cytometric determination of nuclear DNA content in interphase cells and the analysis of chromosome numbers in mitotic cells after removal of the chemicals and subculture showed that oryzalin is the most efficient chromosome doubling agent followed by APM and colchicine in that order.
Abstract: The data on mitotic blocking, induction of micronuclei, and chromosome doubling after treatments of transformed potato suspension cells with three different anti-microtubule agents oryzalin, amiprophos-methyl (APM) and colchicine are reported. The fast growing cell suspension line 413 with high mitotic activity is used, which contains various T-DNA introduced genetic markers (kanamycin resistance, β-glucuronidase activity, hairy root phenotype, hormone autotrophy, opine production). When compared to colchicine (0.5–5.0 mM), oryzalin and APM (15–32 μM) arrested the cells in metaphase more efficiently, induced micronucleated cells at higher frequencies and yielded a greater number of micronuclei. Flow cytometric determination of nuclear DNA content in interphase cells and the analysis of chromosome numbers in mitotic cells after removal of the chemicals and subculture showed that oryzalin is the most efficient chromosome doubling agent followed by APM and colchicine in that order. The anti-microtubule properties of the spindle toxins and interrelationship of various cellular events are discussed in relation to the mechanisms and factors involved in mitotic blocking, micronucleation and chromosome doubling.
90 citations
TL;DR: A monoclonal anti-actin antibody, previously shown to recognize M. grisea actin, bound specifically to filasomes concentrated in the peripheral cytoplasm of subapical regions, and to the core-region of the Spitzenkörper.
Abstract: We have successfully localized fungal actin for the first time using immuno-electron microscopy and hyphal tips of the rice blast pathogenMagnaporthe grisea. Following ultrarapid freezing, samples were processed in a novel substitution fluid of 10% acrolein in anhydrous ethanol and embedded in LR White resin. A monoclonal anti-actin antibody, previously shown to recognizeM. grisea actin, bound specifically to filasomes concentrated in the peripheral cytoplasm of subapical regions, and to the core-region of the Spitzenkorper.
87 citations
TL;DR: The purpose of this paper is to establish clear definitions, identify synonyms, and indicate homologies where possible about the cytoskeleton of protists.
Abstract: The terminology used to describe the cytoskeleton of protists is sometimes redundant and confusing. The independent origins of protistology from studies on algae, fungi, and protozoans led to these problems. Additionally, recent studies indicate that seemingly unrelated taxa form new, monophyletic groups. However, homologous structures that support monophyly are difficult to identify when the literature is published in journals restricted to specific fields or when the terminology is in duplicate or triplicate. The purpose of this paper is to establish clear definitions, identify synonyms, and indicate homologies where possible.
86 citations
TL;DR: It is hypothesize that a euglenoid with features similar to those now present in P. cantuscygni was ancestral to both the eugenoid and kinetoplastid lines.
Abstract: The euglenoids and kinetoplastids form a diverse assemblage of organisms which show no obvious phylogenetic relationship with other flagellates. An ultrastructural examination and comparison of the flagellar apparatus, the feeding apparatus, and mitotic nucleus indicate a number of shared morphological features which support a common ancestry for the two groups. Of particular interest is the euglenoid, Petalomonas cantuscygni, which shares many of the ultrastructural features common to both groups. Based on the data presented, we hypothesize that a euglenoid with features similar to those now present in P. cantuscygni was ancestral to both the euglenoid and kinetoplastid lines.
85 citations
TL;DR: Double immunogold labeling of tubulin and actin in rapidly frozen and freeze-substituted pollen tubes of Nicotiana alata is utilized in an attempt to clarify the distribution and association of these cytoskeletal proteins.
Abstract: It is well known that an extensive array of actin microfilament (MF) bundles exists in the cytoplasm of pollen tubes and that it plays an important role in cytoplasmic streaming in these cells. Less well documented or understood is a cortical MF system, which occurs in two forms: single fine filaments running the length of the cortical microtubules (MTs), and MF bundles. In the present study we have utilized double immunogold labeling of tubulin and actin in rapidly frozen and freeze-substituted pollen tubes ofNicotiana alata in an attempt to clarify the distribution and association of these cytoskeletal proteins. We find that both antibodies bind to antigens associated with cortical MTs, while generative cell MTs label only with the tubulin antibody. Bundles of MFs that show a clear reaction with anti-actin are often seen associated with the cortical MTs, but it remains unclear if the single MT-associated MFs are labeled, and thus, if they are composed of actin. Nevertheless, a majority of cortical MTs show a close association with actin and it is possible that these MTs act as guide elements for MF bundles.
81 citations
TL;DR: In giant-cells in roots of the four host species examined in this study, feeding tube morphology was identical and an elaborate membrane system was associated with the feeding tubes and was most extensive around newly formed tubes.
Abstract: The plant pathogenic nematodeMeloidogyne incognita forms conspicuous tubular structures referred to as feeding tubes in special food cells, called giant-cells, induced and maintained in susceptible host roots by feeding nematodes. Feeding tubes are formed by nematode secretions injected into giant-cells via a stylet and apparently function to facilitate withdrawal of soluble assimilates by the parasite. In giant-cells in roots of the four host species examined in this study, feeding tube morphology was identical. Tubes were straight to slightly curved structures just less than 1 μm wide and up to slightly more than 70 μm long. At the ultrastructural level, each tube consisted of a 190–290 nm thick, electron-dense, crystalline wall surrounding an electron-transparent lumen with a diameter of 340–510 nm. The distal end of the tube was sealed with wall material. Older tubes were found free in the host cytoplasm while the proximal ends of young tubes were attached to the host cell wall via short wall ingrowths through which the nematode's stylet was inserted. An elaborate membrane system was associated with the feeding tubes and was most extensive around newly formed tubes. Contiguous to the feeding tube wall, this membrane system consisted of strands of smooth endoplasmic reticulum while rough endoplasmic reticulum predominated toward the outer margin of the membrane system. Vacuoles and mitochondria were excluded from a zone of cytoplasm surrounding feeding tubes. This zone of exclusion, as well as the membrane system noted above, tended to be less pronounced or absent around older tubes no longer being used by the nematode.
TL;DR: Immunofluorescence microscopy with a monoclonal antibody raised against the PSTAIR sequence, which corresponds to a peptide conserved in the p 34cdc2 protein kinase throughout the phylogenetic scale including higher plants, showed that the width of p 34CDc2 band was narrower than that of MT band.
Abstract: Immunofluorescence microscopy with a monoclonal antibody raised against the PSTAIR sequence, which corresponds to a peptide conserved in the p 34cdc2 protein kinase throughout the phylogenetic scale including higher plants, was used to study the intracellular localization of p 34cdc2 during the cell cycle in onion root tip cells. Although p 34cdc2 was evenly distributed in the cytoplasm throughout the cell cycle, a more intense staining was observed in the cortical region, where the preprophase band of microtubules (MTs) was located. Double staining with the PSTAIR and plant tubulin antibodies showed that the width of p 34cdc2 band was narrower than that of MT band. These data raise the interesting question regarding the possible role of p 34cdc2 protein kinase in determining the division site in plant cells.
TL;DR: A phylogenetic classification based upon a cladistic analysis suggests that aquatic fungi are natural members of the chromophyte group.
Abstract: The cytoskeleton of flagellate chromophyte algae, zoospores and gametes is active during swimming, phototaxis, several types of phagotrophic feeding, the formation, secretion and deployment of silica-scales, and the abrupt movement of spine-scales. The flagellar basal bodies are anchored by microtubular roots and/or fibrous roots. The kinds, numbers, and paths of these roots are characteristic of different taxonomic groups within the chromo-phytes. There are more differences in flagellar apparatuses for taxonomic classes dominated by flagellates as compared to classes dominated by coccoid, filamentous, or parenchymatous forms. Swimming cells that exhibit phototaxis often contain an autofluorescent substance that is located at the base of one flagellum. Phagotrophy occurs in flagellates of several distantly related taxonomic classes, suggesting that phagotrophy evolved independently several times. The most complex phagotrophic process occurs in the Chrysophy-ceae where one microtubule of a flagellar root forms a feeding basket or pouch into which food particles are moved. The silica-scales of the Synurophyceae are formed, secreted and finally moved into position outside the cell by cytoskeletal components. The six spine-scales of Apedinella (Pedinellophyceae) lie outside the plasma membrane, but they are attached by microligaments and are repositioned almost instantly by a cytoskeletal complex of actin, centrin, and microtubules. A phylogenetic classification based upon a cladistic analysis suggests that aquatic fungi are natural members of the chromophyte group.
TL;DR: Staining of nuclei with DAPI in combination with the protein fluorochrome sulforhodamine 101 allows bi-parametric analysis of nuclear DNA and protein in higher plants.
Abstract: High-resolution flow cytometry of nuclear DNA in higher plants has been performed from chopped plant tissues and plant protoplasts. A preparation and staining procedure with the DNA specific fluorochrome DAPI, successfully employed for precise flow cytometric DNA analysis of animal and human cells has been used in a slightly modified manner for the DNA analysis of plant cell material. High-resolution DNA histograms coefficients of variation about 1–1.5% have been obtained routinely from plant species with different DNA content. Staining of nuclei with DAPI in combination with the protein fluorochrome sulforhodamine 101 allows bi-parametric analysis of nuclear DNA and protein. The described simple and precise method might be very promising for the analysis of DNA in basic and applied cytogenetic investigations of plant cell research.
TL;DR: It is concluded that the pyrenoid functions as a unique metabolic compartment of the chloroplast in which the reactions of the photosynthetic carbon reduction pathway are initiated.
Abstract: RuBisCo activase catalyzes the activation and maintains the activated state of the photosynthetic enzyme ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCo, EC 4.1.1.39). We employed antisera prepared against the RuBisCo holoenzyme purified from tobacco and RuBisCo activase isolated from spinach to determine the localization of these proteins in leaves of C3-type higher plants and green algae. In leaves ofVicia faba, both RuBisCo activase and RuBisCo are distributed throughout the chloroplast stroma. In contrast, RuBisCo activase and RuBisCo are predominantly localized to the pyrenoid in the green algaeChlamydomonas reinhardtii andColeochaete scutata. The co-immunolocalization of RuBisCo activase and RuBisCo to the pyrenoid in these two green algal species suggests that pyrenoid-localized RuBisCo is catalytically competent. We conclude that the pyrenoid functions as a unique metabolic compartment of the chloroplast in which the reactions of the photosynthetic carbon reduction pathway are initiated.
TL;DR: The results suggest that the destruction of chloroplast DNA, which occurs approximately 48 h before leaf yellowing, could be due to the activation of some metallo-nucleases and, furthermore, this enzymatic degradation propels the leaf towards senescence.
Abstract: The second leaf ofOryza sativa develops, grows and ages within the 10 days that follow imbibition under our controlled continuous-light conditions. Proplastids in the leaf cells develop, mature to become chloroplasts and then age and disintegrate. In an examination of this life process, we studied first the behavior and the number of copies of plastid DNA and levels of chlorophyll by epifluorescence microscopy after staining with 4′,6-diamidino-2-phenylindole (DAPI), and by fluorimetry with a video-intensified microscope photon-counting system (VIMPCS). The results indicated that the number of copies of the plastid DNA per plastid increased and reached to plateau value of approximately 100 at the time when the elongation of the mesophyll cells and the enlargement of chloroplasts ceased 96 h after imbibition. However, 24 h later, the number of copies of plastid DNA per chloroplast began to decrease and fell rapidly to approximately 30 copies within 168 h after imbibition. Our examination of the number of chloroplasts per mesophyll cell indicated that no division of chloroplasts occurred more than 72 h after imbibition. The results suggest that the decrease in number of copies of plastid DNA per chloroplast was not due to an increase in the number of chloroplasts, but that this decrease was caused by degradation by unidentified enzymes. Since visible senescence of leaves, which was characterized by development of a yellowish color, began 168 h after imbibition, the degradation of plastid DNA seemed to occur 48 h before the visible leaf senescence. When we tested the nucleolytic activities in the second leaves after imbibition by digestion of plasmids in vitro and DNA-SDS polyacrylamide gel electrophoresis, five Ca2+−, four Zn2+−, and four Mn2+−dependent nucleases were detected in the leaf blades, and one of the Ca2+−, two of the Zn2+−, and two of the Mn2+−dependent nucleases were also identified in a purified preparation of intact chloroplasts. When the activity of the Zn2+−dependent nucleases (51 kDa and 13 kDa) increased markedly, degradation of the plastid DNA occurred. These results suggest that the destruction of chloroplast DNA, which occurs approximately 48 h before leaf yellowing, could be due to the activation of some metallo-nucleases and, furthermore, this enzymatic degradation propels the leaf towards senescence.
TL;DR: Immunogold labelling has been used to study the cellular and subcellular localization of myrosinase using LR-White acrylic resin and ultrahin sections from four different species of Brassicaceae, and showed that the antiserum was specific against myosinase from these species.
Abstract: Immunogold labelling has been used to study the cellular and subcellular localization of myrosinase (β-thioglucosidase, EC 3.2.3.1), using LR-White acrylic resin and ultrahin sections from four different species of Brassicaceae;Brassica napus L.,Sinapis alba L.,Raphanus sativus L., and B.oleracea L. For immunolabelling, a polyclonal antibody raised in rabbit against a highly purified myrosinase fromSinapis alba was used. Western blots showed that the antiserum was specific against myrosinase from these species. Ultrathin sections were sequentially incubated with anti-myrosinase antiserum and with secondary antibodies conjugated with colloidal gold. Gold label was present in typical myrosin cells both in radicles and in cotyledons when observed in the electron microscope. The intracellular localization showed that myrosinase was present in myrosin grains in the myrosin cells in all four species of Brassicaceae.
TL;DR: In this article, an extensive darkly-staining matrix which filled prominent intercellular spaces of the root cortex, gradually decreasing through a transition zone into the nodule cortex.
Abstract: Root nodules are induced in actinorhizal plants by the nitrogen-fixing actinomyceteFrankia. Nodules may be initiated by root hair infection or by intercellular penetration. InCeanothus spp. (Rhamnaceae),Frankia colonized the host root tissue by intercellular infection, in spite of the occurrence of root hairs in the infected region. The intercellular infection pathway was characterized by an extensive darkly-staining matrix which filled prominent intercellular spaces of the root cortex, gradually decreasing through a transition zone into the nodule cortex. At the ultrastructural level, most of the matrix was composed of fibrillar electron dense material. Holes or spaces occurred in the electron dense matrix, often in conjunction with apparent loosening of wall layers. Secondary cell division was observed within the root cortical cells embedded in the intercellular matrix. Unusually high levels of pectic compounds and proteins were identified histochemically in the matrix.
TL;DR: The phragmoplasts consist of co-aligned microtubules and F-actin organized into bundles that are broad proximal to the midplane and taper distally as discussed by the authors.
Abstract: Cytokinesis in microsporocytes of moth orchids is unusual in that it occurs simultaneously after meiosis, the cytoplasm does not infurrow in the division planes, and cell plates are deposited in association with centrifugal expansion of phragmoplasts. Microtubules radiating from the nuclear envelopes appear to be of fundamental importance in establishment of division planes. Primary interzonal spindles develop between sister nuclei and interaction of radial microtubules triggers development of secondary interzonal spindles between non-sister nuclei. From three to six or more phragmoplasts, depending upon the arrangement of nuclei in the coenocyte, develop from these postmeiotic arrays. The phragmoplasts consist of co-aligned microtubules and F-actin organized into bundles that are broad proximal to the mid-plane and taper distally. Ultrastructure of the phragmoplast/cell plate reveals that abundant ER is associated with vesicle aggregation and coalescence. Cell plates are deposited in association with phragmoplasts as they expand centrifugally to join the parental wall and/or fuse with one another in the interior of the cell.
TL;DR: The dinoflagellate FA can be compared to the FA of the cryptomonads, chrysophytes, and the ciliates for phylogenetic purposes and immunomicroscopical investigations of the microtubular, actin and centrin components of the din oflageLLate cytoskeleton point to the comparative usefulness of these cytological features.
Abstract: SummaryModern microscopical approaches have allowed more accurate investigations of the three-dimensional nature of the dinoflagellate flagellar apparatus (FA) and several other cytoskeletal protein complexes. Our presentation overviews the nature of the dinoflagellate FA and cytoskeleton in a number of taxa and compares them with those of other protists. As with other protists, the FA of the dinoflagellates can be characterized by the presence of fibrous and microtubular components. Our studies and others indicate that the dinoflagellate FA can be expected to possess a striated fibrous root on the basal body of the transverse flagellum and a multimembered microtubular root on the basal body of the longitudinal flagellum. Two other features that appear widespread in the group are the transverse striated root associated microtubule (tsrm) and the transverse microtubular root (tmr). The tsrm extends at least half the length of the transverse striated root while the tmr extends from the transverse basal body toward the exit aperture of the transverse flagellum. In most cases, the tmr gives rise to several cytoplasmic microtubules at a right angle. The apparent conserved nature of these roots leads us to the conclusion that the dinoflagellate FA can be compared to the FA of the cryptomonads, chrysophytes, and the ciliates for phylogenetic purposes. Of these groups, the chrysophytes possess an FA with the most structures in common with the dinoflagellates. Our immunomicroscopical investigations of the microtubular, actin and centrin components of the dinoflagellate cytoskeleton point to the comparative usefulness of these cytological features.
TL;DR: The immunoblot results showed that the levels of tubulin and actin monomers in thecold-treated tubes were comparable to those present in the control tubes, which might be a prerequisite for the rapid recovery of the structure and function of the cytoskeleton recorded after the return of the cold-treated pollen tubes to normal temperature.
Abstract: In 3-and 12-hour-old pollen tubes ofNicotiana tabacum microtubules (MTs) most resistant to cold-depolymerization were located in the generative cell (GC). The most cold-sensitive MTs occurred in the apical region of the pollen tube. In the basal part of the tube, the cold-resistance of MTs increased, especially in 12-hour-old tubes. The cold depolymerization pattern of MTs with accumulation of tubulin at the cell and nuclear membranes suggested that binding of MTs to membranes might increase their stability. The IIF microscopy and staining with fluorochrome-conjugated phallotoxins indicated that microfilaments (MFs) unlike MTs remained polymerized in cold-treated pollen tubes. Recording of the positions of the vegetative nucleus (VN) and GC in the control and cold-treated pollen tubes in different ages showed clearly that low temperature stopped sharply the movement of the VN and GC into the young tubes while no drastic effects were recorded in the old tubes. The cessation and recovery of the movement correlated well with de-and reassembly of MTs, which indicated that MTs in addition to MFs may be necessary for the movement of VN and GC. The immunoblot results showed that the levels of tubulin and actin monomers in the cold-treated tubes were comparable to those present in the control tubes, which might be a prerequisite for the rapid recovery of the structure and function of the cytoskeleton recorded after the return of the cold-treated pollen tubes to normal temperature.
TL;DR: All essential procedures for a transformation system of barley based on microinjection into microspores have thus been performed successfully and the technical feasability of intranuclear microin injection was demonstrated by injecting the fluorescent dye Lucifer Yellow.
Abstract: In order to identify microspores, suitable for transformation via microinjection of DNA, single microspores of barley (Hordeum vulgare L.) were selected after initial preculture of anthers floating on liquid media and analysed for their development in individual culture in microdroplets of culture medium. Conditions for microculture and plant regeneration from single selected embryogenie microspores were established. The technical feasability of intranuclear microinjection was demonstrated by injecting the fluorescent dye Lucifer Yellow. All essential procedures for a transformation system of barley based on microinjection into microspores have thus been performed successfully. Further efforts to increase efficiencies of culture and microinjection procedures are necessary, however, in order to improve the suitability of this approach towards transformation of barley.
TL;DR: A homogenizing medium containing very low ionic strength, low monovalent ion (K+) concentration, a 3-fold higher level of Mg+ +, the presence of EGTA to chelate Ca++, and PMSF to inhibit protease activity is introduced.
Abstract: A procedure is introduced which allows the isolation of abundant amounts of F-actin from plants (etiolated pea seedlings) in an array of morphologies very similar to the array of morphologies found in situ. The major feature is a homogenizing medium containing very low ionic strength, low monovalent ion (K+) concentration, a 3-fold higher level of Mg+ +, the presence of EGTA to chelate Ca++, and PMSF to inhibit protease activity. Using this buffer, about 80–90% of the sedimentable actin is found in the low speed (4,000×g) pellet.
TL;DR: A novel mitochondrial plasmid of about 16 kbp was apparently responsible for promoting mitochondrial fusion inPhysarum polycephalum, and was transmitted to all mitochondria without any structural change.
Abstract: We have identified a novel mitochondrial plasmid of about 16 kbp inPhysarum polycephalum. This plasmid was apparently responsible for promoting mitochondrial fusion. Only in strains carrying the plasmid, small spherical mitochondria fused with one another to form large knotted multinucleate mitochondria which subsequently nderwent fusion between the areas (mt-nuclear) that contained the mitochondrial DNA (mtDNA) derived from individual mitochondria. Several successive mitochondrial divisions followed, accompanied by mt-nuclear divisions. The resulting mitochondria contained recombinant mtDNAs, but the plasmid was transmitted to all mitochondria without any structural change.
TL;DR: Within the infected nodule cortical cells, (poly)galacturonate content of the interfacial encapsulation surrounding theFrankia endosymbiont was very high, while the cell walls were not labeled above background, suggesting that the encapsulation is a specialized wall layer.
Abstract: During early stages of nodule development inCeanothus spp., theFrankia infection pathway is characterized by a distinctive host-derived extracellular matrix. In the present study, a major component of the host interface is shown to consist of pectic polysaccharides. The distribution of these pectic polysaccharides in developing nodules has been delineated in root and nodule tissue. The levels of polygalacturonic acid detected were extremely high in the root mucilage and in the intercellular infection matrix in the root cortex, as detected by indirect immunogold localization with an antibody, and with fluorescein-conjugated alginate and pectate probes. Polygalacturonans in the intercellular matrix and in nodule tissue were predominantly esterified. The non-esterified polygalacturonans were located in cell junctions. Within the infected nodule cortical cells, (poly)galacturonate content of the interfacial encapsulation surrounding theFrankia endosymbiont was very high, while the cell walls were not labeled above background, suggesting that the encapsulation is a specialized wall layer.
TL;DR: Wound callus, generated by the innermost layer, increased markedly in the last two weeks of culture and concomitantly formed vascular clumps surrounded by meristematic layers; these produced root primordia which were frequently anomalous (day 26–27).
Abstract: Internode stem expiants ofNicotiana tabacum cv. Samsun, consisting of eight cell layers: epidermis, subepidermal chlorenchyma, collenchyma and cortical parenchyma (i.e., thin cell layers), were cultured under conditions inducing rhizogenesis. The aim was to investigate the histological sequence of adventitious root formation in this system. The earliest cytological events in culture (12 h) were nucleolar extrusions and amitotic nuclear divisions. Though not restricted to a specific cell layer, the two phenomena were more frequent in the subepidermal chlorenchyma, and characterized the first phases (12-96 h) of cell proliferation mainly occurring in this layer. Amitoses were followed by the formation of thin walls within the original cells, resulting in the formation of intracellular clusters. These subepidermal clusters were separated by enlarged cells of the parent tissue, whose nuclei showed nucleolar extrusion. At day 3 the first mitoses were observed in cells having abundant starch inclusions. Amitotic divisions also continued, but less frequently. The increasing frequency of mitoses in the subepidermal chlorenchyma (day 4), as well as in the two underlying collenchymatous layers, contributed to the growth of the superficial clusters, in which small clumps of meristematic cells were formed; these, later (day 9), gave rise to root domes. The 5th cell layer remained undivided for a relatively long time (two weeks). The 6th and 7th layers proliferated mitotically later (from day 8 onwards) than the superficial layers and formed root domes following the same histological sequence. Wound callus, generated by the innermost layer, increased markedly in the last two weeks of culture and concomitantly formed vascular clumps surrounded by meristematic layers; these produced root primordia which were frequently anomalous (day 26–27). Regardless of its origin (i.e., superficial or deep layers of the expiant, or wound callus cells), root tip formation was always preceded by the differentiation of a sheath of starch-containing cells, from which the root cap developed.
TL;DR: Changes in the distribution and organization of the microtubule and F-actin microfilament cytoskeletons reflect a change in cell function following signal reception for appressorium, and the reorientation of the cytoskeleton likely dictates the change incell morphology.
Abstract: Formation of appressoria inUromyces appendiculatus is triggered by external physical features of host stomata as well as artifical surfaces bearing inductive topographies. Microtubule and F-actin microfilament cytoskeletons were examined for their involvement in the process of appressorium formation in this fungus, using laser scanning confocal and electron microscopy. In germlings not stimulated to form appressoria the microtubule and microfilament cytoskeletons were organized as filaments mostly oriented parallel to the longitudinal axis of the cell. Following contact of the germling apex with an inductive topographical signal, e.g., 0.5 μm high ridge, the microtubules and F-actin filaments in the cell apex nearest the substrate appeared randomly oriented. Microtubules farther from the substrate remained oriented parallel to the longitudinal axis of the cell. In later stages of appressorium development, many cytoskeletal elements became oriented parallel to the inductive ridge, especially near the substrate. In regions farther from the substrate in these same cells, the microtubules and microfilaments were arranged in a reticulate pattern. Changes in the distribution and organization of the microtubule and F-actin microfilament cytoskeletons reflect a change in cell function following signal reception for appressorium. The reorientation of the cytoskeleton likely dictates the change in cell morphology.
TL;DR: It is demonstrated that HRGP2b antigens can be localized over the cell wall of both dicot and monocot hosts, although they mostly occur in the contact zone in infected samples, which means that the contact Zone can be regarded as an apoplastic space presenting a structural response to the symbiotic mycorrhizal status.
Abstract: When vesicular-arbuscular mycorrhizal (VAM) fungi colonize the cortical cells of their host plant roots, the hyphae are separated from the host cytoplasm by the invaginated host plasmalemma and interfacial material. The presence of hydroxyproline rich glycoproteins (HRGPs) at the interface was investigated with a polyclonal antibody obtained against melon callus HRGP2b. By using a combination of cytochemical methods, antigens were detected in pea, in both the presence and absence ofGlomus versiforme, a mycorrhizal fungus. For comparison, observations were performed in parallel with leek as a monocot host. Antigens were localized over the pea cell wall in root tissues. At the ultrastructural level, gold granules were mostly present in the periplasmic space. In mycorrhizal plants, the most substantial deposition occurred at the interface between the fungal wall and the host membrane. Dot blot experiments revealed HRGP2b antigens in soluble root fractions from both uninfected and mycorrhizal samples.
TL;DR: The cytokinetic apparatus in microsporogenesis lacks a preprophase band of microtubules and the selection of cytokinetics planes is dependent upon disposition of nuclei which define cytoplasmic domains via post-meiotic radial systems ofmicrotubules.
Abstract: The cytokinetic apparatus in microsporogenesis lacks a preprophase band of microtubules and the selection of cytokinetic planes is dependent upon disposition of nuclei which define cytoplasmic domains via post-meiotic radial systems of microtubules. Meiotic cytokinesis was investigated in hybrid moth orchids (Phalaenopsis) exhibiting irregular patterns of cytokinesis. In these polliniate orchids, spindle orientation is imprecise, and the tetrad nuclei (therefore the microspores) may be in rhomboidal, tetrahedral or linear arrangement. The hybrid “Sabine Queen” (section Phalaenopsis) regularly undergoes simultaneous cytokinesis, as is common in orchids. The hybrid “Vista Rainbow” (section Amboinenses) produces either a complete dyad wall, a partial wall, or no wall after first nuclear division. In all cases, a first division phragmoplast is initiated in the interzonal region and expands centrifugally into the peripheral cytoplasm. Fluorescence microscopy shows that the phragmoplast consists of fusiform bundles of microtubules and Factin bisected by a non-fluorescent zone. If a cell plate fails to form, a band of organelles polarized in the equatorial region effectively divides the cell into two domains. The organelles disperse when a dyad wall is complete, but tend to remain polarized around an incomplete wall. In four-nucleate coenocytes, the usual interzonal microtubules between sister nuclei (primary) form slightly in advance of secondary arrays between non-sister nuclei. Phragmoplasts are initiated in sites defined by the post-meiotic microtubule arrays.
TL;DR: Flagellar propulsion takes place in the viscosity-dominated realm of low Reynolds number fluid dynamics, with a great variety of beat patterns, functionally adapted hydrodynamically or in other ways for locomotion, feeding, and other more restricted roles.
Abstract: SummaryFlagellar propulsion takes place in the viscosity-dominated realm of low Reynolds number fluid dynamics. Volumes of fluid are carried in a capture zone around the moving regions of the flagellum, and the flagellar motion achieves propulsion because some of that water is shed from the capture zone, either from the flagellar tip in typical flagellar motion or to the side reached at the end of the effective stroke in the case of ciliary motion. Helical flagellar motion is in principle more efficient than planar beating, and the rotation caused by the former introduces complications in propulsion that may be advantageous, e.g., inEuglena, or disadvantageous, e.g., in a fixed cell. The presence of a surface near to the moving organelle restricts the fluid motion, but this effect enhances ciliary propulsion. There is a great variety of beat patterns, functionally adapted hydrodynamically or in other ways for locomotion, feeding, and other more restricted roles.