bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pollen-stigma interactions inBrassica oleracea:I. ultrastructure and physiology of the stigmatic papillar cells
Authors: Roberts Ian N. , Harrod Gillian , Dickinson Hugh G. 
Published: April 2021

ABSTRACTThe osmotic potential (Ψπ) of the stigmatic papillar cells of Brassica oleracea is —14·8 bars. In laboratory conditions each cell transpires water at rates within the range from 3 × 10−5 to 5 × 10−5 mm3h−1. A small increase in transpiration rate is detected following cross-(compatible) but not self-(incompatible)pollination. No significant changes in Ψπ occur following pollinations of either compatibility.Electron microscopy reveals an active papillar cytoplasm apparently secreting proteins into the cell wall via small vesicles. The cuticle is discontinuous and freeze-fracture techniques indicate that channels transverse the cell wall, suggesting a possible pathway for the movement of protein molecules of high molecular weight from the cytoplasm to the stigma surface.Analysis of electron-microscopic autoradiographs of mature, self-incompatible papillae following pulse-chase experiments with L-[3H]leucine and treatment with cycloheximide shows that protein molecules secreted into the cell wall may return to the cytoplasm at a later stage. The significance of these results is discussed in terms of current models of the pollen·stigma interaction in Brassica.
The presence and location of sporopollenin in fruiting bodies of the cellular slime moulds
Authors: Maeda Yasuo 
Published: April 2021

ABSTRACT
The presence of an acetolysis-resistant polymer (sporopollenin) in the cellular slime moulds is demonstrated. This polymer is located on the stalk sheath of fruiting bodies as a bundle of fine fibrils (4–5 nm diameter). The location and structure of sporopollenin in spores are shown to vary considerably, depending upon the species. In Polysphondylium violaceum spores, sporopollenin is composed of fine spicules (4–5 nm in diameter, 25–5 0 nm long) that cover both the outermost layer of spore wall and the inner surface of the cell membrane. The sporopollenin of Dictyostelium discoideum spores is located preferentially close to the inner surface of the cell membrane, forming a mass of electron-opaque fine granules (4–5 nm in diameter). D. mucoroides spores, however, appear not to possess a tight network of sporopollenin, since they were less resistant to acetolysis than those of the other species. The biological significance of the results is discussed with special reference to fruiting body formation.
Globin synthesis in heterokaryons formed between chick erythrocytes and human k562 cells or rat l6 myoblasts
Authors: Lanfranchl Gerolamo , Linder Stig , Ringertz Nils R. 
Published: April 2021

ABSTRACT
Chick globin synthesis was studied in heterokaryons formed between chick erythrocytes and human K562 erythroleukemia cells or rat L6J1 myoblasts. It was found that chick globin synthesis was activated after fusion of definitive (17 to 19-day) chick erythrocytes obtained from 17 to 19-day embryos with K562 cells. Chick globins appeared to be of the adult βA, α D and β types, whereas no embryonic globin synthesis could be detected.
The pattern and time-course of globin synthesis was investigated after fusion of 4 to 5-day embryonic erythrocytes with rat L6J 1 myoblasts. The level of globin synthesis was high at early time points but then decreased. Globin synthesis, however, was still detectable at 9 days in these heterokaryons. Chick βA, α D and ε-globin chain synthesis was observed both at early and late time points after fusion.
Asymmetric distribution of gap junctions amongst identified photoreceptor axons of Lucilia cuprina (diptera)
Authors: Shaw S. R. 
Published: April 2021

ABSTRACT
The relative number of gap junctions within the ring of axon terminals of identified adult photoreceptors has been counted, in the lamina cartridges of Liucilia cuprina. Terminals are similar in size, but some pairs of terminals make up to four times as many junctions with each other as do other pairs; the frequency of connection varies markedly along the length of the cartridge. Junctions across the cartridge occasionally occur out of the normal sequence, frequently in the upper cartridge between one pair of axons. The distributions suggest that mechanical factors transmitted down from the upper cartridge are responsible for the non-uniformities. There may be indiscriminate competition between terminals at some stage of development for a fixed quota of junctions, the groupings of which have to reach a minimum size to remain viable. Amongst the neurones of the cartridge, great specificity is shown in which cells form gap junctions: only receptors Rl–6 are involved, making junctions only with each other. Within this class Rl·6, however, there is no evidence from the distribution of gap junctions for unique cell labelling, that distinguishes one photoreceptor from another. Connections appear to form indiscriminately, on the basis of proximity. This same generalization holds true for a particular class of chemical feedback synapse. The identity of tight-junction-like structures on the photoreceptor axon membrane is also discussed.
Demonstration Of Lymphocyte Surface Lectins That Recognize Sulphated Polysaccharides
Authors: Parish* Christopher R. , Rylatt Dennis B. , Snowden John M. 
Published: April 2021

ABSTRACT
Cholate extracts of murine lymphocytes were shown to contain haemagglutinating activity against autologous erythrocytes. The species specificity and sugar inhibition pattern of the haemagglutinin closely paralleled the specificity of autorosetting, an interaction that had been shown previously to involve the recognition by lymphocytes of carbohydrate structures on autologous erythrocytes. The probable identity of the haemagglutinin and autorosetting receptors was confirmed by experiments utilizing the unique plasma protein autorosette inhibition factor, which appears to block both interactions by masking carbohydrate acceptor sites on erythrocytes.
Detailed sugar inhibition studies revealed that the haemagglutinin and autorosetting receptors have a high affinity for certain sulphated polysaccharides, such as heparin and dextran sulphate. Since similar sulphated polysaccharides have been shown previously to inhibit lymphocyte recirculation, a possible role for these receptors in lymphocyte homing and recirculation is discussed.
Addition of a mannose-6-phosphatecontaining oligosaccharide alters cellular processing of low density lipoprotein by parental and ldl-receptor-defective chinese hamster ovary cells
Authors: Leichtner A.M. , Krieger M. 
Published: April 2021

ABSTRACT
Low density lipoprotein (LDL) was chemically modified by the addition of ω-(6-phospho)· tetra(αl -3)mannosyl-(αl -2)mannose (M56P), a phosphorylated oligosaccharide containing a terminal mannose 6-phosphate residue. Uptake and degradation of this modified LDL (M56P-LDL) by Chinese hamster ovary (CHO) cells occurred via the lysosomal enzyme (mannose 6-phoβphate) receptor pathway. Cellular processing of M56P-LDL was saturable, specific for the mannose 6-phosphate marker, and occurred with approximately threefold higher affinity than that of native LDL by the LDL receptor pathway. Mannose 6-phoβphate receptor activity, as measured by degradation of M56P-LDL, was ninefold lower than the LDL receptor activity. Degradation of M56P-LDL was more sensitive to inhibition by the lysosomotropic agent chloroquine than was degradation of LDL, suggesting differences in the intracellular processing of mannose 6-phosphatebearing ligands and LDL. Previously isolated CHO cell lines defective in LDL receptor activity resembled parental CHO cells in their ability to process M56P-LDL. The potential use of M56P-LDL in the isolation of cells with pleiotropic mutations affecting receptor-mediated endocytosis is discussed.
Localization of concanavalin a binding carbohydrate in chlamydomonas flagella
Authors: Millikin Blake E. , Weiss Richard L. 
Published: April 2021

ABSTRACT
Chlamydomonas flagella are shown to possess two zones of concanavalin A (ConA) binding carbohydrate. The first zone, distinguished by a requirement for a prolonged labelling period for visualization of fluorescein isothiocyanate (FITC)-ConA fluorescence, is localized in the flagellar coat. The second zone is characterized by a rapid FITC- and [125I]ConA labelling subsequent to disruption of the flagellar membrane, but is unaffected by reagents that act only on the flagellar surface coat. Electron microscopy and ferritin-ConA labelling indicate that this subsurface zone is localized between the flagellar membrane and axoneme in the space that we term the flagelloplasm. These results are used to suggest possible functions for ConA binding glycosyl residues in flagella.
Loss of differentiating nematocytes induced by regeneration and wound healing in Hydra
Authors: Fujisawa Toshitaka , David Charles N. 
Published: April 2021

ABSTRACT
Cell death was observed in the nematocyte differentiation pathway in Hydra during head and foot regeneration. This death occurs throughout the regenerating piece, is transient in nature and is selective for committed stenotele and desmoneme precursors. Proliferating nematoblasts are unaffected. Cell death appears to be caused by release of a toxic factor rather than loss of a hormone required for differentiation, since regenerating pieces released a factor that inactivated differentiating nematocytes, and injured animals that had intact head and foot tissue also lost differentiating nematocytes. The inactivated nematocytes are removed by phagocytosis by epitheliomuscular cells.
Arginine synthesis by hepatomas in vitro: I. The requirements for cell growth in medium containing ornithine in place of arginine and the isolation and characterization of variant hepatomas auxotrophic for arginine
Authors: Goss S. J. 
Published: April 2021

ABSTRACT
Cell growtH in ‘ornitHine-medium’ requires tHe expression of two liver-specific genes, tHose for ornitHine transcarbamoylase (OTC) and carbamoyl pHospHate syntHetase I (CPS-I). CPS-II appears unable to replace CPS-I in tHis system. THe need for ?√-acetylglutamate (to activate CPS-I) can be met, at least in part, by providing it in tHe medium. THe otHer gene products involved in arginine biosyntHesis are probably all ubiquitous (i.e. not tissue-specific). In an attempt to study tHe factors responsible for tHe expression of liver-specific genes, variant Hepatomas are isolated tHat Have lost tHe ability to grow in ornitHine-medium. Two classes of ‘orn -’ variants are identified: unstable variants tHat require dexametHasone for adequate CPS-I production, and ‘stable’ variants tHat Have lost many liver-specific traits. Studies on one stable variant sHow tHat it can revert (tHougH rarely), and tHat it regains its various liver-specific traits in a non-coordinate fasHion.
Resistance of mouse lymphoma l5178yaii cells to alkylation with methylmethane sulphonate resides in a late step of excision repair
Authors: Pearson C. M. , Styles J. A. 
Published: April 2021

ABSTRACT
The mutant mouse lymphoma cell line (L5178YAII), resistant to X-rays, ultraviolet light and alkylating agents, was reinvestigated in an attempt to establish the nature of the mutation. These cells were compared with P388 mouse lymphoma cells, which exhibit normal sensitivity to these mutagens. A series of studies was conducted to compare DNA alkylation and strand breakage with cell survival after exposure of the two cell lines to methylmethane sulphonate.
It was found that neither the degree of alkylation nor the removal of the common alkylation products was correlated with the different sensitivities observed in these cell lines. A correlation was established between cell killing and the production of long-lived strand breaks. P388 cells were found to accumulate twice as many long-lived strand breaks compared to L5178YAII cells, at equal levels of alkylation. This suggested that long-lived strand breaks were the major toxic lesions.
Further experiments indicated that these long-lived strand breaks were produced by a process consistent with excision repair. Evidence is also presented that indicates that the mutation in L5178 YAI I cells that is responsible for their resistance may occur in ligase activity or its associated ADP-ribosyl transferase system.
Circus movements in dissociated cells from two new hybrid frog embryos
Authors: Johnson Kurt E. , Adelman Mark R. 
Published: April 2021

ABSTRACT
Circus movements are a peculiar kind of cell movement, seen in many amphibian cells, that involve the formation of a hyaline protrusion from the cell surface and rotation of this blister around the circumference of the cell. Studies of cells from normal Ranapipiens embryos have shown a close correlation between circus movements in vitro and gastrulation related cell movements in vivo. Cells from two developmentally arrested hybrid embryos (R. pipiens ♀ ×R, sylvatica ♂and R pipiens ♀ × R. catesbiana ♂) are deficient in circus movements to an extent that corresponds to their gastrulation deficiencies. This study reports on the preparation of two new hybrids (R. pipiens ♀ × R. temporaria ♂ (temp) and R. pipiens ♀ × R. clamitans ♂ (clam)). Cells from temp embryos show some circus movements but the proportion of cells displaying such movements does not increase with increasing developmental age to the same extent as is seen in cells from normal embryos. Cells from clam embryos show very few circus movements at any developmental age. These aberrations in the onset and extent of circus movements are discussed in relation to characteristic morphogenetic events that occur in normal embryos and in these two new arrested hybrid embryos.
Altered labelling of the cell surface and intracellular organelles with [3H]Mannose in enucleated amoebae
Authors: Flickinger Charles J. 
Published: April 2021

ABSTRACTThe production, transport, and disposition of material labelled with [3H]mannose were studied in microsurgically enucleated and control amoebae. Cells were injected with the precursor and samples were prepared for electron-microscope radioautography at intervals, up to 24 h later. Control cells showed heavy labelling of the rough endoplasmic reticulum and the Golgi apparatus at early intervals after injection. Later, labelling of groups of small vesicles increased, and the percentage of grains over the cell surface peaked 12 h after administration of the precursor. Two major changes were detected in enucleate amoebae. First, the kinetics of labelling of cell organelles with [3H]mannose were altered in the absence of the nucleus. The Golgi apparatus and the cell surface both displayed maximal labelling at later intervals in enucleates, and the percentage of grains over the rough endoplasmic reticulum varied less with time in enucleated than in control cells. Second, the distribution of radioactivity was altered. A greater percentage of grains was associated with lysosomes in enucleates than in control cells. The change in the kinetics of labelling of the endoplasmic reticulum, Golgi apparatus and cell surface indicates that intracellular transport of surface material was slower in the absence of the nucleus. It is suggested that this is related to the decreased motility of enucleate cells.
Post-pollination callose development in ovules of Rhododendron and Ledum (Ericaceae): Zygote special wall
Authors: Williams E. G. , Knox R. B. , Kaul V. , Rouse J. L. 
Published: April 2021

ABSTRACT
In Rhododendron spp. and Ledum groenlandicum a callose wall is laid down around the zygote in the first 2 days after fertilization. The periodic acid/Schiff-positive, aniline blue-fluorescence-positive callosic wall is initiated adjacent to the degenerating synergid, extends to cover the entire zygote surface, and remains visible during the initiation of embryogeny as the zygote elongates before the first proembryonal division. Unfertilized ovules show eventual callose deposition in the ovule wall cells during senescence in undeveloped abscising pistils, but show no development of callose within the embryo sac. Possible roles of a zygote special callose wall are discussed.
Ultrastructural changes during formation and germination of microcysts in Polysphondylium pallidum, a cellular slime mould
Authors: Hohl H.R. , Miura-Santo L. Y. , Cotter D. A. 
Published: April 2021

ABSTRACT
Ultrastructural changes during encystation of Polysphondylium palltdum, a cellular slime mould, include an increase in fibnllar material in the cytoplasmic matrix, the formation of cytoplasms microprojections at the cell periphery and the occurrence of tiny vesicles and some larger vacuoles near the cell periphery. The cyst wall appears first as a fluffy, loose network of fibrils. In the mature cyst it consists of a dense inner and a somewhat looser outer layer. It contains inclusions of apparently cytoplasmic origin. Electron-dense material lines the cell periphery beneath the plasma membrane. Excystment of the myxamoeba is accompanied by a swelling of aggregated vacuoles and polyvesicular bodies, the disappearance of the peripheral cytoplasmic lining, and a general loosening of the wall texture. For a limited period the cisternae of the rough endoplasmic reticulum appear highly dilated. The loosened wall eventually breaks and the myxamoeba emerges by extending pseudopodia through the rupture, leaving the entire cyst wall behind.
Kinetochore ultrastructure in vincristine-treated mammalian cells
Authors: Journey L.J. , Whaley Audrey 
Published: April 2021

ABSTRACT
The ultrastructure of chromosomes from tissue culture cells blocked in division with vincristine sulphate or colchicine was examined. Kinetochores had a distinctive morphology consisting of trilaminar dense plates closely applied to the chromosomes. In longitudinal sections, kinetochores appeared as separate plates attached to opposite sides of the chromosomes. In transverse sections of some prometaphase chromosomes, however, the kinetochore resembled an incomplete ring-like structure encircling the chromatid pair. These observations indicate that sister kinetochores may be continuous during early stages of their formation.
X-ray diffraction and electron-microscope studies of the brush border membrane of guinea pig intestinal epithelial cells
Authors: Limbrick A. R. , Finean J. B. 
Published: April 2021

ABSTRACT
Low-angle X-ray diffraction patterns have been obtained from condensed systems of brush border membranes which contain up to 30 % water and also from hydrated samples of the lipid extracts of the membranes. The diffraction bands obtained from the hydrated membranes were orders (up to n = 8) of a lamellar repeating unit of about 30 nm which included 2 membrane units. By referring to electron micrographs of these condensed membrane preparations, an electron density profile of the brush border membrane has been evaluated, and its significance in relation to the molecular organization of the membrane is discussed.
Mutations induced in amoeba proteus by the carcinogen N-methyl-N-nitrosourethane
Authors: Ord M. J. 
Published: April 2021

ABSTRACT
Mutations have been induced in single amoebae by treatment with the powerful mutagen, N-methyI-N-nitrosourethane. Three mutants, which differ visibly from the parent strain to the extent that individual amoebae are recognizable and change of characteristics from normal to mutant or mutant to normal can be followed in single cells, are described. These mutant strains have been cultured in the laboratory, using Tetrahymena feeding, without loss of mutant characteristics for over 2 years, undergoing some 100 or more cell cycles. Hybrids made between mutants and the parent strain, using the nuclear transfer technique, are viable and stable. They showed that in all cases crosses between normal and mutant amoebae retained the characteristics of the mutant only if the mutant nucleus was present. Though amoebae from 2 of the mutant strains may revert to normal form with increase in temperature or change to a wheat culturing technique, these ‘apparent normal’ amoebae resume the mutant form on a return to the temperature and feeding conditions normally used.
The interaction between mutant and control amoebae was observed in heterokaryons over periods of up to 6 weeks by cutting off pieces of the heterokaryon cytoplasm at regular intervals to prevent division while allowing growth. In general the presence of a control nucleus led to the development of normal characteristics whether the heterologous nuclei were contained in control or mutant cytoplasm. No antagonistic action occurred between mutant and control nuclei when sharing the same cytoplasm. Study of the clones formed by the offspring of heterokaryon divisions showed the mutant and control nuclei unaltered by long periods of close contact. These experiments indicate the chromatin as the site of action of the mutagen. A possible mode of action of the mutagen in amoebae, relating to the functional state of the DNA, is suggested.
Macromolecular physiology of plastids: VI. changes in membrane structure associated with shifts in the absorption maxima of the chlorophyllous pigments
Authors: Henningsen K. W. 
Published: April 2021

ABSTRACT
Dispersal of the prolamellar body tubules into primary lamellar layers has been studied in leaves of dark-grown bean seedlings (Phaseolus vulgaris L.). Following complete photoconversion of protochlorophyllide the dispersal process can proceed in either light or darkness. The dispersal is reversibly inhibited in leaves at 0°C. Above o °C the time course for the dispersal is temperature dependent. The spectral shift of the in vivo absorption maximum of newly formed chlorophyllide from 684 to 672 nm is also inhibited at o °C and the time course is temperature-dependent in a manner similar to that of the membrane dispersal. A causal connexion between the 2 phenomena can thus be suggested. Derangement of the tubular membranes produced by heat treatment or by freezing and thawing in darkness causes the appearance of photoactive protochlorophyllide absorbing at 635 nm. Photoconversion of protochlorophyllide 635 nm results in chlorophyllide absorbing at 672 nm and further dissociation of the membranes. Denaturation of the prolamellar body membranes by heating or by slow thawing results in the formation of photoinactive protochlorophyllide absorbing at 632 nm.
An inverse relation between cell density and the number of microvilli in cultures of BHK21 hamster fibroblasts
Authors: O’neill C. H. , Follett E. A. C. 
Published: April 2021

ABSTRACT
The relationship between culture density and the number of microvilli on the cell surface has been studied using BHK21 cells in established monolayer culture. The number of microvilli can be estimated quantitatively by a scanning electron-microscope technique. It can be increased by applying specific antiserum, but whether antibody is applied or not a significant number of cells regularly bear microvilli. This number is characteristic of the culture density. In sparse cultures above a certain minimum density it is relatively high, and in confluent cultures it is much reduced. These results indicate that microvilli may be inhibited by cell contact.