Showing papers in "Protoplasma in 1982"
TL;DR: It is suggested that while typical bipolar embryos are generally not formed, plant regeneration nevertheless takes place through embryogenesis and the precocious germination of the embryoids, which are considered modifications of the scutellum, a definitive part of the cereal embryo.
Abstract: Tissue cultures ofTriticum aestivum L. (wheat) initiated from young inflorescences and immature embryos possessed the potential for regeneration of whole plants. Both a friable and a compact type of callus were produced on Murashige and Skoog's medium with 2 mg/l 2,4-dichlorophenoxyacetic acid. The friable callus contained meristematic centers in which the peripheral cells ceased dividing, elongated, and could be easily separated. Roots were frequently formed in this type of callus. The compact, yellowish, and nodular callus arose from the epithelial and sub-epithelial cells of the embryo scutellum, and the rachis and glumes of the young inflorescence. Such callus had a smooth surface and characteristic chlorophyllous areas. Plants were regenerated only from the compact callus. The first sign of differentiation in the compact callus was the formation of a cleft or notch on the smooth surface, followed by the appearance of trichomes and the direct development of leafy structures which were not associated initially with any shoot meristems. Multiple shoots subsequently arose at the bases of the leafy structures, which are considered modifications of the scutellum, a definitive part of the cereal embryo. Accordingly, we suggest that while typical bipolar embryos are generally not formed, plant regeneration nevertheless takes place through embryogenesis and the precocious germination of the embryoids. Plants regenerated from immature embryo and inflorescence cultures were grown to maturity in soil, and were shown to have the normal chromosome number of 2n=6x=42.
315 citations
TL;DR: Electron microscopic observations show that elements of ER become loosely associated with aggregating dictyosome vesicles at the onset of plate formation, and structural observations support the idea that during formation of the plasmodesma a tubular element of ER is tightly furled upon itself and its inner leaflet is compressed into a rod.
Abstract: The association of endoplasmic reticulum (ER) with the developing cell plate has been analyzed in lettuce roots fixed in glutaraldehyde and post-fixed in a mixture of osmium tetroxide-potassium ferricyanide (OsFeCN). Electron microscopic observations show that elements of ER, which are selectively stained by the OsFeCN reagent, become loosely associated with aggregating dictyosome vesicles at the onset of plate formation. Subsequently the ER, in a tubular reticulate network, surrounds the vesicular aggregates creating a three dimensional membrane matrix. It is suggested that the ER (1) provides a structural framework that holds the vesicles in position and directs their fusion within the plane of the plate and/or (2) regulates the local release of calcium ions required for vesicle fusion. OsFeCN post-fixation also provides new information about the cell plate vesicles themselves. The results demonstrate that vesicles derived from dictyosomes undergo an abrupt increase in staining as they fuse at the plate. Finally the ER associated with developing and mature plasmodesmata has been examined. Electron micrographs reveal that the OsFeCN staining, seen traversing the cell plate in early stages, later becomes restricted from that portion of the ER extending through the plasmodesmatal canal. These structural observations support the idea that during formation of the plasmodesma a tubular element of ER is tightly furled upon itself and that its inner leaflet is compressed into a rod. The ER cisternal space appears occluded and thus it is argued that intercellular transport occurs through the cytoplasmic annulus of the plasmodesmata.
212 citations
TL;DR: Following a 5 hours ethylene treatment, cortical cells of Pea showed a change in the orientation of both microtubules near the plasma membrane and recently deposited cellulose microfibrils, which may be early enough to constitute the primary effect of ethylene leading to radial cell expansion.
Abstract: Following a 5 hours ethylene treatment, cortical cells of Pea (Pisum sativum L. var Alaska) epicotyl third internode showed a change in the orientation of both microtubules near the plasma membrane and recently deposited cellulose microfibrils. Control cortical cells had mostly transverse microtubules. The ratio of the average frequency of transverse to longitudinal microtubules was 6.0. After 5 hours of ethylene treatment, cortical cells had mostly longitudinal microtubules, with the ratio of transverse to longitudinal microtubules equal to 0.1. Epidermal cells were more variable than cortical cells with regard to the frequency of longitudinal and transverse microtubules. Observation of cortical cell walls in conventionally stained thin sections revealed that recent deposition of microfibrils had been primarily transverse in almost all of the control cortical cells sampled. In contrast, more than half of the ethylene-treated cortical cells had recent deposition oriented primarily longitudinally. This change in microtubule and microfibril orientation may be early enough to constitute the primary effect of ethylene leading to radial cell expansion.
148 citations
TL;DR: A model is proposed for the structure of the plasmodesmata of Azolla root primordia, based on micrographs obtained by a combination of fixation in glutaraldehyde/p-formaldehyde/tannic acid/ferric chloride, digestion of cell walls and the use of stereo pairs, indicating that the model is geometrically feasible.
Abstract: A model is proposed for the structure of the plasmodesmata ofAzolla root primordia, based on micrographs obtained by a combination of fixation in glutaraldehyde/p-formaldehyde/tannic acid/ferric chloride, digestion of cell walls and the use of stereo pairs. Unlike the model for plasmodesmatal structure proposed byRobards (1971), the desmotubule is depicted as a virtually closed cylindrical bilayer providing little or no open pathway for transport. In this respect it is similar to the model ofLopez-Saez
et al. (1966). An analysis of the molecular packing of types of lipids found in endoplasmic reticulum (of which the desmotubule is an extension) indicates that the model is geometrically feasible. Details cannot be discerned with accuracy, but material, possibly particulate, occupies much of the space between desmotubule and plasma membrane, the cytoplasmic lumen being reduced to inter-particle spaces of cross-sectional area comparable to that of the bore in a gap junction connexon. Implications for intercellular transport are discussed.
128 citations
TL;DR: It is hypothesized that the material occluding the plasmodesmata constitutes the diffusion barrier, by presenting a hydrophilic environment which allows passage of molecules with maximum molecular weights of 700–800 daltons, but which retains those with aromatic side groups.
Abstract: SummaryInvestigations into plant intercellular communication were initiated through an examination of plasmodesmata and cell-to-cell passage of molecular probes in the staminal hairs ofSetcreasea purpurea. Plasmodesmata connecting staminal hair cells of small buds are filled with an electron-opaque homogenous material. To examine the permeation selectivity of plasmodesmata, molecular probes made up of fluorescein isothiocyanate (FITC) complexed with amino acids and peptides were injected into the staminal hair cells and the spread of these fluorescent molecules through the symplast, was monitored. Molecules composed of FITC complexed to single amino acids with polar and aliphatic R groups travel rapidly, while those which include peptides travel slowly. Dye molecules composed of an amino acid with an aromatic side group do not pass from cell to cell at all. It is hypothesized that the material occluding the plasmodesmata constitutes the diffusion barrier, by presenting a hydrophilic environment which allows passage of molecules with maximum molecular weights of 700–800 daltons, but which retains those with aromatic side groups.
106 citations
TL;DR: Detergent-activated UDPase activity provides a more reliable, less cumbersome way to monitor Golgi membranes compared to cold storage-activation and this marker can be used on fresh preparations.
Abstract: The distribution of latent UDPase activity (cold storage-activated) is similar to Triton-stimulated UDPase activity in membrane fractions separated by differential centrifugation as well as fractions purified by linear sucrose density centrifugation. The Triton-stimulated UDPase activity appears to be a specific marker for Golgi membranes in corn root homogenates. Detergent-activated UDPase activity provides a more reliable, less cumbersome way to monitor Golgi membranes compared to cold storage-activation and this marker can be used on fresh preparations.
76 citations
TL;DR: Peripheral cells of the secretory complex are modified into a protective sheath with thick walls and large vacuoles, while their plastids are differentiated from leucoplasts into typical amyloplasts.
Abstract: Oil glands ofCitrus deliciosa are multicellular secretory structures, globular to oval in shape, in the centre of which an essential oil-accumulating space is formed. Opening of this space begins from a single cell. It undergoes lysis which later extends to the neighbouring gland cells.
76 citations
TL;DR: There is evidence that the embryogenic tissue, and ultimately the embryos, are of multicellular origin, which appears to be contradictory to the often stated view that somatic embryos generally arise from single “committed” cells.
Abstract: Immature leaf explants ofSorghum bicolor (L.) Moench can be stimulatedin vitro to form roots, shoots or embryos. When the cultures were maintained with the high 2,4-D level which was essential for optimal culture initiation, the organs or embryos proliferated as suppressed primordia, but they could always be identified by simple histological means. Perivascular cells of comparatively old but still immature leaf sheath regions appeared to be strongly determined to form adventitious roots or root-type “callus” cultures. We have evidence that the embryogenic tissue, and ultimately the embryos, are of multicellular origin. This ontogeny of the embryos appears to be contradictory to the often stated view that somatic embryos generally arise from single “committed” cells. The implications of these findings for basic and applied research on cereal tissue culture are discussed.
76 citations
TL;DR: There is a predictable and well defined variation in numbers of plasmodesmata in roots of Azolla, and some suggestion that plasmodemata may be less resistive towards the apical cell than away from it is given.
Abstract: There is a predictable and well defined variation in numbers of plasmodesmata in roots ofAzolla. As the apical cell of the root ages, it lays down walls with progressively fewer plasmodesmata, thereby gradually cutting itself off from the rest of the root (Gunning 1978). Electrical coupling was examined between the apical cell and an adjacent merophyte in roots of various lengths. The apical cell becomes increasingly electrically isolated from the rest of the root as it ages. Electrical coupling is strongly correlated with the number of the plasmodesmata between the coupled cells. The resistance of a plasmodesma, as estimated from equivalent electrical circuits, was 150–600 times more resistive than a value based on theoretical considerations. No evidence was found for a change in the physiology of plasmodesmata as the root ages. Coupling experiments, both on root hairs and at the apex, gave some suggestion that plasmodesmata may be less resistive towards the apical cell than away from it.
62 citations
TL;DR: When Ca2+, K+ or Cl− was injected iontophoretically into the cytoplasm of intact Nitella cell, only Ca2+ reversibly inhibited the cy toplasmic streaming, but when an extremely large current was used, the cyToplasmics streaming was reversibly inhibition irrespective of the ion species.
Abstract: When Ca2+, K+ or Cl− was injected iontophoretically into the cytoplasm of intactNitella cell, only Ca2+ reversibly inhibited the cytoplasmic streaming. However, when an extremely large current was used, the cytoplasmic streaming was reversibly inhibited irrespective of the ion species. This inhibition may be due to a transient increase of free Ca2+.
60 citations
TL;DR: Isolated P-particles move anodically in an electrical field, and the possibility that their movement from the grain to the tube tip during growth depends on a potential gradient, already demonstrated for lily pollen tubes, is considered.
Abstract: Numerous polysaccharide-rich particles (“P-particles”) occur in the tip region of growing grass pollen tubes, where they apparently contribute to the extending wall. In other families the corresponding bodies have been shown to originate from dictyosome activity during pollen tube growth. However, in the grasses the main synthesis precedes anthesis; the P-particles represent up to 30% of the reserves of the vegetative cell of the dormant grain, numbering over one million in the pollen grain of rye. Their membranes are incomplete. The polysaccharide content, which is initially coarsely granular but becomes microfibrillar with hydration, is readily extracted with ammonium oxalate, and is probably pectic in nature. Simple methods for isolating the particles in relatively pure populations are described. Hydrolysis yields principally galactose, arabinose, glucose, and rhamnose. Apart from proteins derived from the original bounding membranes, a protein fraction is tenaciously bound to the polysaccharide. Isolated P-particles move anodically in an electrical field, and the possibility that their movement from the grain to the tube tip during growth depends on a potential gradient, already demonstrated for lily pollen tubes, is considered.
TL;DR: Growth and thus cytomorphogenesis inMicrasterias seem to be mediated by a patterned accumulation of Ca2+ at the periphery of the differentiating cell.
Abstract: Developing cells ofMicrasterias denticulata Breb. show a characteristic fluorescence of the plasma membrane (or cortical protoplasm) after treatment with chlorotetracycline (CTC), which is known to be an indicator for membrane-bound Ca2+. Depending on the stage of development the fluorescing sites of the young half cell are distributed in a specific pattern which corresponds to cell pattern formation. Therefore growth and thus cytomorphogenesis inMicrasterias seem to be mediated by a patterned accumulation of Ca2+ at the periphery of the differentiating cell. Participation of Ca2+ in a membrane-recognition process responsible for local vesicle incorporation is discussed.
TL;DR: Results support the most recent theories on the mechanism of locomotion in outline only and suggest numerous cytoplasmic vesicles, with fibrillar contents, react strongly with a polysaccharide specific stain; their distribution in the cell and poly Saccharide content suggest these may be the source of raphe and sheath material.
Abstract: Generation of movement in benthic diatoms is thought to be intimately associated with secretion at the raphe, a slit in the silica cell wall. The presence and distribution of extracellular substances and their source was investigated cytochemically by transmission electron microscopy. Extracellular material, possibly-acid mucopolysaccharide, was observed consistently within the entire length of the raphe of both valves and also as a sheath enveloping the silica frustule. Such quantities of extracellular material are absent in conventionally fixed motile diatoms. Numerous cytoplasmic vesicles, with fibrillar contents, distributed peripherally but concentrated along the raphe and at the cell poles, react strongly with a polysaccharide specific stain; their distribution in the cell and polysaccharide content suggest these may be the source of raphe and sheath material. Results support the most recent theories on the mechanism of locomotion in outline only; the details cannot be clarified. Localization procedures using alcian blue and silver staining of peroxidised sections are discussed briefly.
TL;DR: The secondary cell wall layer of the young root hair of Equisetum hyemale has a helicoidal texture and the cortical microtubules in these hairs maintain an axial alignment while microfibrils are being deposited with a different orientation in each subsequent layer.
Abstract: The secondary cell wall layer of the young root hair ofEquisetum hyemale (L) has a helicoidal texture. The cortical microtubules in these hairs maintain an axial alignment while microfibrils are being deposited with a different orientation in each subsequent layer. The role of cortical microtubules in microfibril orientation is disputed.
TL;DR: A method for improved, ice-crystal-free cryofixation of various biological materials (macromolecules, subcellular fractions, whole cells in suspensions or as monolayers) without any chemical pretreatments is evaluated.
Abstract: We evaluate a method for improved, ice-crystal-free cryofixation of various biological materials (macromolecules, subcellular fractions, whole cells in suspensions or as monolayers) without any chemical pretreatments. The principle of the method (as introduced byPscheid, Schudt, andPlattner 1981 for cell monolayer cultures) is as follows. Firstly, a thin sample layer is sandwiched between a thin copper object holder and a thermally insulating plastic sheet (Thermanox, which is also used as a cell culture substratum); secondly, a jet of melting propane is shot from a simple, inexpensive brass vessel onto the copper object holder. We now ascertained that this simple and inexpensive method allows cooling rates up to > 18,000 °C/sec and, thus, gives better results than comparable but more sophisticated and expensive procedures. The method also avoids all the disadvantages of some other rapid freezing methods. Specifically, the sample mass required is minimal, the sample remains fully hydrated and no changes of ionic or other conditions can occur. There is no hazard of passing a cold gas phase (cooling curves being very steep right at the beginning) or of impairment by mechanical impact (as it could be with “cold metal block freezing”). The expedient of using a thermal insulator as part of a sandwich sample allows cooling rates which are superior or at least equivalent to those obtained with a commercial double propane-jet device (and double copper sandwiches). The reason for this is that in practice a two-side propane jet onto a copper-copper sandwich can not reach both sides precisely at the very same time (as implied from our cooling rate measurements). The tentative transformation of our mono-jet into a double-jet variation (with a branched nozzle piece) did also not improve the results, when compared with a single propane-jet onto a copper-Thermanox sandwich.
TL;DR: It could be shown that during differentiation the leaf tissue rapidly loses the ability to respond to conventional tissue culture techniques, probably related to a loss of sensitivity towards 2,4-D, an otherwise most potent growth regulator in tissue culture.
Abstract: In this paper we present further studies on the generation of tissue cultures from leaves of the cerealSorghum bicolor (L.) Moench. It could be shown that during differentiation the leaf tissue rapidly loses the ability to respond to conventional tissue culture techniques. This was probably related to a loss of sensitivity towards 2,4-D, an otherwise most potent growth regulator in tissue culture. The immature tissue which proved to be sensitive proliferated over a wide range of concentration with a broad optimum of about 0.6–6 mg 1−1 2,4-D. This concentration range appears to be only slightly higher than that described for many dicotyledonous tissue cultures. The relevance of these findings is discussed with reference to the well known dual function of 2,4-D, namely as a selective herbicide and a potent artificial auxin. The implications of these attributes to the practical application of cereal tissue culture is stressed.
TL;DR: Three algae collected as part of a natural phytoplankton assemblage were found to differ in their cytological responses to low dose short-term exposure to copper and lead, with Fragilaria more sensitive to copper than to lead.
Abstract: Summary Three algae, Melosira granulata, Fragilaria capucina, and Anacystis cyanea, collected as part of a natural phytoplankton assemblage were found to differ in their cytological responses to low dose shot>term exposure to copper and lead. In general, all were more sensitive to copper than to lead. Fragilaria was more sensitive to both metals than the other species examined. Most immediate changes in relative volume categories can be ascribed to changes in vacuole volume that are most likely the result of changes in membrane permeability. There was some degree of accommodation in all three species at 24 hours. These results are discussed in view of the natural environment of the algae, as well as in relationship to previous studies.
TL;DR: Secretory cavities of Citrus deliciosa seem to originate from a pair of meristematic cells (an epidermal cell and a second one placed under it) which undergo successive divisions resulting in the formation of a globular/oval gland situated in the parenchyma, and a conical stalk, which joins the gland with the epidermis.
Abstract: Secretory cavities ofCitrus deliciosa seem to originate from a pair of meristematic cells (an epidermal cell and a second one placed under it). These cells undergo successive divisions resulting in the formation of a globular/oval gland situated in the parenchyma, and a conical stalk, which joins the gland with the epidermis. The young gland consists of a central group of polyhedral cells ensheathed by layers of radially flattened cells. During the early differentiation stages of the gland cells a close association of cytoplasmic microtubules with various organelles is observed. Plastids increase progressively in number and size and their matrix locally contains tubular networks accompanied by small oil droplets. In peripheral cytoplasm numerous myelin-like lomasomes have been observed. Peripheral cells of the gland are gradually modified from the inner cells following a different developmental pattern. Their walls become thicker and plastids do not contain tubular complexes, but only a few thylakoids partly surrounding the newly formed starch grains.
TL;DR: The antennal sensilla inI.
Abstract: The antennal sensilla inI. typographus are almost exclusively confined to the flattened terminal flagellar segment. The sensillar types have distinct distribution patterns in the three areas where they are found. Judging from the ultrastructural characteristics the following functions can be assigned to the sensillar types: chemoreception, single-walled and double-walled sensilla; chemoreception/mechanoreception, terminal-pore sensillum. Moreover there are two types of mechanoreceptors, one of which is connected to a bristle, whereas the other terminates within the cuticle of the flagellar segment.
TL;DR: Histological information is presented on the origin of initial tissue proliferation and on embryogenesis and organogenesis in sub-cultured tissue derived from mature orchardgrass embryos and on somatic embryos completely isolated from the tissue mass suggestingde novo embryogenesis.
Abstract: Histological information is presented on the origin of initial tissue proliferation and on embryogenesis and organogenesis in sub-cultured tissue derived from mature orchardgrass (Dactylis glomerata L.) embryos. Embryos were plated on an LS agar medium containing 20 μM 2,4-D. Examination of cultures between 96 and 144 hours after plating showed parenchyma proliferation originating primarily from the coleorhiza, especially the basal portion. Within 28 days after plating, the tissue showed various degrees and kinds of organized structures including lobed meristematic regions with vascular tissue. These are thought to develop ultimately into aerial roots which are common in grass tissue cultures. Subcultured tissue on 1.0 μM 2,4-D medium showed somatic embryos completely isolated from the tissue mass suggestingde novo embryogenesis. Organogenesis was evident by shoot apical meristems existing on the surface of the tissue mass without attached roots and root meristems without shoots within the tissue. The observations are discussed in relation to the anatomy of the grass embryo.
TL;DR: It is suggested that calcium provides the linkage between underlayer scales and rod-shaped scales inTetraselmis.
Abstract: The structure and topography of flagellar scales (underlayer scales, rodshaped scales, hair-scales) in the green flagellateTetraselmis cordiformis has been studied in detail and the effect of divalent cations and fixation conditions on scale structure and topography was followed quantitatively. Hair-scales occur in two rows on opposite sides of a flagellum and are linked to the flagellar membrane and to two axonemal doublets by B-tubule-flagellar membrane connectives. Underlayer scales form about 24 longitudinal rows along the flagellum and occur in two distinctive shapes (pentagonal and square). The square shaped underlayer scales are related in position to the attachment sites of the hair-scales. Rod-shaped scales occur in about 20 longitudinal rows along the flagellum and are characteristically positioned as “double scales”. Calcium in the culture medium is necessary to retain rod-shaped scales on the flagellum, absence of calcium or chelation with EGTA or pyrophosphate leads to disappearance of rod-shaped scales from the flagellum. Other divalent cations can only partially substitute for calcium. It is suggested that calcium provides the linkage between underlayer scales and rod-shaped scales inTetraselmis. Flagellar scales inTetraselmis apparently fall into two categories: a) hair-scales (not affected by fixation or absence of divalent cations, firmly bound to axonemal microtubules via the flagellar membrane), b) underlayer scales and rod-shaped scales (affected by fixation and absence of divalent cations, kept on the flagellum mainly by electrostatic forces). The function of flagellar scales inTetraselmis is discussed.
TL;DR: The active sites of actin of oneCharaceae species were found to interact with the endoplasmic factor from a different species, which irreversibly inhibited reconstitution of the cytoplasmic streaming.
Abstract: The active sites of actin of oneCharaceae species were found to interact with the endoplasmic factor from a different species. Protoplasm was suqueezed out of cells ofChara australis with vacuoles that had been perfused beforehand with a medium containing EGTA and Mg · ATP. Centrifugation of this protoplasmic mixture divided it into the supernatant composed of endoplasmic granules and the precipitate composed of chloroplasts and nuclei. When the endoplasmic granular aggregates were introduced into a tonoplast-freeNitella axilliformis cell treated with NEM to inactivate the endoplasmic factor, they became attached to theNitella gel and streamed longitudinally with the polarity. Treatment of the endoplasmic granules with the strong Mg2+chelator CyDTA (1,2-cyclohexane diamineN, N′-tetraacetic acid) irreversibly inhibited reconstitution of the cytoplasmic streaming.
TL;DR: An extensive system of microtubules develops during meiotic prophase in the mossRhynchostegium serrulatum, which contributes to the establishment of moss sporocyte polarity.
Abstract: An extensive system of microtubules develops during meiotic prophase in the mossRhynchostegium serrulatum (Hedw.)Jaeg. &Sauerb. Development of the cytoskeleton can be traced to early prophase when the nucleus is acentric and the single plastid divides into four plastids. The cytoskeletal microtubules are associated with equidistant positioning of the four plastids at the distal tetrad poles and with migration of the nucleus to a central position in the sporocyte. The cytoskeleton, which interconnects plastids and encloses the nucleus, contributes to the establishment of moss sporocyte polarity. Just prior to metaphase I evidence of the prophase cytoskeleton is lost as the bipolar metaphase I spindle develops in association with discrete polar organizers located in opposite cleavage furrows between plastids.
TL;DR: It is proposed that EDG at plant cell membranes have a certain resemblance to the Ca2+-bs revealed by the same method on plasma membrane of a variety of animal cells.
Abstract: Different cytochemical methods were employed to demonstrate the existence of Ca2+-binding sites (Ca2+-bs) at the membranes of barley root tip cells, involving addition of CaCl2 (10 mM or 1 mM) to all aqueous solutions used for tissue processing for electron microscopy, treatment of ultrathin sections by Ca-chelating agents, enzymic digestion of ultrathin sections and modification of Wachstein-Meisel procedure for localization of Ca2+-dependent ATPase activity. Addition of 10 mM CaCl2 to the fixatives and rinsing solutions causes electron-dense globules (EDG) to be formed in a variety of cells, those in cortical cells being associated mainly with the plasma membranes, in root cap cells with the plasmalemma as well as with majority of intracellular membranes. The obligatory presence of EDG at the membranes of Golgi vesicles and secretory vesicles approaching plasmalemma was revealed in the secreting root cap cells. Besides, electron opaque connecting material was found between the plasmalemma and adjacent secretory vesicle membranes. In true meristematic cells Ca-supplemented solutions induce formation of EDG localized at the ER membranes, and nuclear and plastid envelopes. In root cells of seeds germinated in the presence of 1 mM CaCl2 electron opaque deposits were found only in local areas of plasmalemma collars around plasmodesmata neck regions, contacting the terminals of subsurface ER channels. In control speciemens (germination, fixation and washing without added CaCl2) EDG were absent in cortical and ground meristem cells, but present in root cap cells, although their number and average size were greatly reduced. Treatment of thin sections by 10mM EGTA or EDTA led to complete removing of EDGs, electron-transparent holes replacing them. Digestion by a variety of proteolytic enzymes and by phospholipase A induced partial destruction of EDG matrices, confirming the presence of protein as well as of phospholipid membrane components. Visualization of electron-dense granular product of cytochemical Ca-ATPase reaction at the same membrane areas where EDG were located suggests that one of the Ca-binding proteins in EDG may represent Ca-ATPase. It is proposed that EDG at plant cell membranes have a certain resemblance to the Ca2+-bs revealed by the same method on plasma membrane of a variety of animal cells. The data obtained are discussed regarding possible regulatory roles of calcium ions in plant cells, especially in exocytotic secretion.
TL;DR: It is demonstrated that Calcofluor also disrupts cell wall assembly in the eukaryotic algaOocystis apiculata, and cells with severely disrupted walls are unable to complete their normal life cycle.
Abstract: Calcofluor White ST is a fluorescent brightener that has previously been shown to alter cellulose ribbon assembly in the bacteriumAcetobacter xylinum. In this report, we demonstrate that Calcofluor also disrupts cell wall assembly in the eukaryotic algaOocystis apiculata. When observed with polarization microscopy, walls altered by Calcofluor show reduced birefringence relative to controls. Electron microscopy has shown that these altered walls contain regions which consist primarily of amorphous material and which generally lack organized microfibrils. We propose that wall alteration occurs because Calcofluor binds with the glucan chains polymerized by the cellulose synthesizing enzymes as they are produced. As a consequence, the glucan chains are prevented from co-crystallizing to form microfibrils. Synthesis of normal walls resumes when Calcofluor is removed, which is consistent with our proposal that Calcofluor acts by direct physical interaction with newly synthesized wall components. Several types of fluorescent patterns at the cell wall/plasmalemma interface have also been observed following Calcofluor treatment. Fluorescent spots, striations; helical bands, and lens-shaped thickenings have been documented. Each of these patterns may be the result of the interaction of Calcofluor with cellulose at different spatial or temporal levels or from varying concentrations of the brightener itself. Helical bands and lens-shaped thickenings also have been examined with the electron microscope. Like other regions of wall alteration, they are found to contain primarily amorphous material. Finally, we note that cells with severely disrupted walls are unable to complete their normal life cycle.
TL;DR: There is no requirement for sustained RNA synthesis by the generative cell nucleus for normal gametophytic development in pollen embryogenesis in cultured anthers of H. niger, it is concluded.
Abstract: The pattern of RNA synthesis during maturation and germination of pollen grains ofHyoscyamus niger was studied using3H-uridine autoradiography. Incorporation of label during pollen maturation was periodic with peak RNA synthesis occurring in the uninucleate, nonvacuolate pollen grains and in the vegetative cell of the bicellular pollen grains. During the early stages of germination, isotope incorporation occurred predominantly in the nucleus of the vegetative cell with little or no incorporation in the generative cell. With the appearance of the pollen tube, incorporation of3H-uridine in the vegetative cell nucleus decreased and completely disappeared at later stages of germination. No incorporation of isotope was observed in the sperms formed in the pollen tube by the division of the generative cell. From a comparison of the results of this study with those of previous works on RNA synthesis during pollen embryogenesis in cultured anthers ofH. niger, it is concluded that in contrast to embryogenic development, there is no requirement for sustained RNA synthesis by the generative cell nucleus for normal gametophytic development.
TL;DR: Normally quiescent cortical tissue of pea roots can be induced, by severing the adjacent vascular cylinder of the root, to undergo redifferentiation to form new files of tracheary and sieve elements which bridge the wound.
Abstract: Normally quiescent cortical tissue of pea roots can be induced, by severing the adjacent vascular cylinder of the root, to undergo redifferentiation to form new files of tracheary and sieve elements which bridge the wound. The development of vascular transfer cells is also induced. Redifferentiation is normally accompanied by division of the original cortical cells. The planes of cell division, especially those preceding sieve element formation, are aligned very precisely in adjacent cells, to produce smooth files of cells. In roots wounded 3–4 mm from the apex, bands of microtubules in the periphery of the cells (pre-prophase bands) form at sites which correspond to the expected planes of cell division.
TL;DR: The development and distribution of calcium oxalate crystals, stomates and hairs were studied in the first trifoliolate leaf of Rhynchosia caribaea using light and transmission electron microscopy.
Abstract: The development and distribution of calcium oxalate crystals, stomates and hairs were studied in the first trifoliolate leaf ofRhynchosia caribaea (Leguminosae: Papilionoideae, Phaseoleae). Using light and transmission electron microscopy, the crystals were shown to occur in both bundle sheath and mesophyll cells. Crystal distribution and shapes are characteristic forRhynchosia. Crystals develop late in leaf development in contrast to the stomates and hairs. As these latter two structures decrease in number per unit area with leaf age, crystal number increases.
TL;DR: The plasmalemma of Nitella internode was made freely permeable to solutes by treating the cell with detergent and EGTA under plasmolysis and the streaming was reactivated by perfusing the exterior of the permeabilized cell with a medium containing both Mg2+ and ATP.
Abstract: The plasmalemma ofNitella internode was made freely permeable to solutes by treating the cell with detergent and EGTA under plasmolysis. After the treatment, the cytoplasmic streaming was stopped by bathing the cell in a medium lacking ATP. The streaming was reactivated by perfusing the exterior of the permeabilized cell with a medium containing both Mg2+ and ATP. The reactivated streaming could be reversibly stopped by depletion of ATP. However, depletion of Mg2+ irreversibly inhibited the streaming.
TL;DR: Kinetic analyses indicate that UDP-Mn2+ is the substrate for the enzyme and characteristics and subcellular location of NDPase activity are discussed in relation to the possible biochemical role of the enzyme.
Abstract: Our previous report indicated a Triton-stimulated NDPase was specifically associated with Golgi membranes isolated from corn roots. Characterization of the enzyme indicates that UDP is the slightly preferred substrate with Mn2+ the preferred divalent cation. Monovalent cations do not further activate the Triton-stimulated UDPase activity. The enzyme has a pH optimum at 6.5 and a temperature optimum between 38–40°C. Kinetic analyses indicate that UDP-Mn2+ is the substrate for the enzyme.