bluuebunny/crossref_metadata_2025_split huggingface dataset:
An ultrastructural study of the differentiation of the spermatozoid of Equisetum
Authors: Duckett J. G. 
Published: April 2021

ABSTRACT
The ultrastructure of spermatogenesis in Equisetum is described with particular reference to the origin and development of the multilayered structure (MLS) and nuclear metamorphosis. Simultaneously with the formation of centrioles, by the fragmentation of the blepharoplast, in young spermatids, the MLS appears in their vicinity. This comprises 4 layers recalling the Vierergruppe of bryophyte spermatids. The outer layer, or microtubular band, consists of juxtaposed microtubules. The three inner lamellar strata, which lie along the anterior edge of the microtubular band, are composed of parallel plates oriented at 35-45° to the axes of the microtubules. Keels are present on the microtubules where these overlie the lamellar layers. A mitochondrion lies subjacent to the lamellar layers and on the outer surface of the anterior edge of the microtubular band is a crest of osmiophilic material. The position of the osmiophilic crest suggests that it may have a role in microtubule synthesis. However, its persistence in the mature gametes after microtubular elongation has ceased, and its banded substructure, reminiscent of flagellar roots, perhaps indicate that its function is mainly mechanical in holding the microtubular band together. Approximately oval in shape and overlain by less than 50 short microtubules initially, the lamellar strata and subjacent mitochondrion rapidly increase in length. Eventually they form a strip 15-20 μm in length overlain by over 300 microtubules. This extensive microtubular band in Equisetum is more likely related to the final shape of the nucleus in the mature gamete than to the presence of numerous flagella. The entire MLS now becomes associated with the nucleus. The microtubular band is closely adpressed to the nuclear envelope and acts as a cytoskeletal framework along which the nucleus undergoes elongation and coiling. Initially the lamellar strip and mitochondrion run along the nuclear envelope with one of their edges touching it and the other projecting into the cytoplasm. However, continuous elongation of the microtubules throughout nuclear metamorphosis results in the gradual separation of the strip and mitochondrion beyond the anterior tip of the nucleus. Simultaneously, the posterior parts of the nucleus become ensheathed by rearward extension of the microtubular band. The centrioles arrange themselves in a single layer on the outer surface of the microtubular band and during the early stages of nuclear metamorphosis give rise to flagella from their distal ends, concomitantly undergoing differentiation into basal bodies. Intense Golgi activity during early and mid-spermatid stages is thought to be related to the accumulation of mucopolysaccharides between the cell wall and cell membrane. In the mid-spermatids rough endoplasmic reticulum is closely associated with the plastids which later accumulate starch, a characteristic feature of spermatogenesis in archegoniate plants.
Autoradiographic evidence for the rapid disintegration of one chloroplast in the zygote of the green alga Ulva Mutabilis
Authors: Bråten T. 
Published: April 2021

ABSTRACT
This paper gives evidence suggesting that one of the two chloroplasts contributed to the zygote of Ulva mutabilis is rapidly destroyed. Chloroplasts in an advanced stage of disintegration can be seen only 4 min after copulation. Radioactive labelling of gametes prior to copulation shows that the disintegrating chloroplast is supplied through the + (plus) gamete, while the chloroplast from the — (minus) gamete is retained in the zygote. These observations are in agreement with genetic observations from the same alga.
Effect of anaerobiosis on respiratory rate, cytochrome oxidase activity and mitochondrial structures in coleoptiles of rice (oryza sativa l.)
Authors: Öpik Helgi 
Published: April 2021

ABSTRACT
An attempt has been made to correlate respiration rate, cytochrome oxidase activity and mitochondrial structure in coleoptiles of rice, Oryza sativa L., germinated under aerobic and anaerobic conditions. The rice coleoptiles emerge from the grain and elongate considerably even under complete anaerobiosis, which totally suppresses root and leaf growth. Cell number, dry weight and nitrogen content per coleoptile are all lowered, although some cell division and translocation of reserves into the coleoptile does take place under anaerobiosis. Compared with coleoptiles from air-grown seedlings, anaerobically grown coleoptiles have a much lower capacity for respiratory oxygen uptake and their cytochrome oxidase activity is depressed even more. Mitochondria, however, are still abundant in 4-day-old anaerobic coleoptiles, with a crista density only slightly lower than in cells of aerobically grown coleoptiles. Since, in the embryonic coleoptile of the ungerminated grain, mitochondria show very little internal structure, a considerable amount of elaboration of mitochondrial structure must occur in the rice coleoptile under anaerobiosis, contrasting with the situation in yeast, where mitochondria of normal structure are formed only in aerobic conditions. Since a high crista density develops in rice coleoptile mitochondria with a very much depressed cytochrome oxidase activity, there is no obligate correlation between crista density and cytochrome oxidase activity in this tissue.
The incorporation of DL-[3-14c]cysteine during spermatogenesis inCeratopteris thalictroides
Authors: Schedlbauer M. D. , Cave Celia F. , Bell P. R. 
Published: April 2021

ABSTRACTRadioactive cysteine fed for 6 h to young gametophytes of Ceratopteris actively producing antheridia was incorporated readily into the early stages of spermatogenesis, but hardly at all into differentiating spermatocytes. Spermatocytes contained only little radioactivity even when the gametophytes were grown for a further 18 h before fixation, thus ensuring that the radioactive label was available at or near the time of their formation. There was some evidence that in very young spermatocytes in the latter material the incorporation was more marked at the periphery of the blepharoplast than elsewhere.The results are interpreted as indicating that the differentiation of the spermatocyte involves little if any net protein synthesis. The proteins of the new structures peculiar to the gamete may thus have been synthesized in earlier stages of spermatogenesis, the last phase of visual differentiation being a consequence of their assembly and organization.
Timing of the first cleavage division of the mouse and the duration of its component stages: A study of living and fixed eggs
Authors: Kaufman M. H. 
Published: April 2021

ABSTRACT
Fertilized mouse eggs were examined between 27 and 34 h after the superovulating injection of human chorionic gonadotrophin (HCG). Out of 1334 eggs examined, 432 were already at the 2-cell stage; the remaining 902 at the i-cell stage were examined in detail. All chromosome preparations of the first cleavage mitosis were classified into groups corresponding with the stages of prometaphase (early and late), metaphase (early or ‘prechromatid’, ‘chromatid’ and ‘late chromatid’) and anaphase.
An indirect estimate was made of the duration of the first cleavage mitosis and of its component stages from the incidence of stages observed at different time intervals after the HCG injection. Fertilized eggs were also observed at 37 °C by time-lapse cine-photography and the interval between the disappearance of the pronuclei and the beginning of telophase of the first cleavage division was determined. The progress of eggs fertilized in vitro was also observed under normal culture conditions. A close correlation was observed between the indirect method of assessing the mitotic time and the direct values obtained from the studies on time-lapse and in vitro culture. The effect of temperature on the mitotic time was also examined by the time-lapse method.
Temperature-sensitive rna polymerase of a mammalian cell mutant
Authors: Naha P. M. 
Published: April 2021

ABSTRACT
In our attempts to characterize a temperature-sensitive mutant (ts-2) of monkey kidney cell line BSC-1, we have provided evidence to show that the mutant was defective in the synthesis or processing of rRNA (45, 28 and 18 s) molecules at 39·5 °C and there was indication that the nucleolar RNA polymerase (I) or some factor associated with its functional activity was thermolabile at the restricted temperature of 39·5 °C. The enzyme in the wild type cell line was, however, stable at this temperature. Though conclusive evidence to implicate RNA polymerase (I) was not obtained in these experiments, temperature-sensitivity tests with crude enzyme extracts of the RNA polymerase in ts-2 showed that it contained a temperature-sensitive factor which was either degraded rapidly or failed to be eluted out of the DEAE-Sephadex column. This temperature-sensitive factor was not affected by α-amanitin.
Cryo-ultramicrotomy of islets of langerhans: some observations on the fine structure of mammalian islets in frozen sections
Authors: Howell S. L. , Tyhurst Margaret 
Published: April 2021

ABSTRACT
A procedure is described for the preparation of ultrathin frozen sections of glutaraldehyde-fixed or unfixed islets of Langerhans by cryo-ultramicrotomy. Freezing of the tissue was accomplished by direct immersion of isolated islets in liquid nitrogen. Sectioning was performed at a specimen temperature of–80 °C and a knife temperature of–40 °C, the ribbon of sections being collected on a trough containing 60 % dimethyl sulphoxide. Staining was accomplished with 4 % silicotungstic acid and sections were protected from drying artifacts by rinsing with 0·5 % polyethylene glycol.
Even in tissue not subjected to prior glutaraldehyde fixation, most of the structural features of A and B cells were well preserved in frozen sections, which were obtained in a number and quality which should render them suitable for ultrastructural, cytochemical or radio-autographic studies.
Quantitative measurement of the course of bean callus differentiation
Authors: Haddon Lindsay E. , Northcote D. H. 
Published: April 2021

ABSTRACT
Two strains of callus have been isolated from bean hypocotyl and grown on a defined maintenance medium supplemented with 2 mg/1. 2:4-dichlorophenoxyaceric acid (2:40) and 2% sucrose. Root initiation was observed in one strain and formation of nodules containing xylem and phloem in both strains after transfer to an induction medium supplemented with 1 mg/1. naphthyleneacetic acid, 0·2 mg/1. kinetin and 3% sucrose, after 3 transfers to maintenance medium.
The number of nodules per gramme increased 10-fold between 6 and 12 days after transfer, and thereafter remained constant. Phenylalanine ammonia lyase (PAL) activity rose to a maximum value when the rate of nodule formation was greatest, and decreased after the maximum nodule concentration was reached. The final constant value for PAL activity was above that of callus grown on maintenance medium, β →3 glucan synthetase activity rose to a maximum 15 days after transfer, and then fell gradually to a level above that measured in callus on maintenance medium.
Callus was transferred from maintenance medium after 3, 4, 5 and 6 transfers. The concentration of nodules after 21 days on induction medium decreased as the callus was kept in culture. No further differentiation could be induced after 6 transfers. The fall in nodule formation was paralleled by a decrease in PAL and β →3 glucan synthetase activities measured 21 days after transfer.
Meiosis in Coprinus vii. the prekaryogamy S-phase and the postkaryogamy dna replication in C. lagopus
Authors: Lu B. C. , Jeng D. Y. 
Published: April 2021

ABSTRACT
The kinetics of incorporation of 32P into DNA have unequivocally shown that the premeiotic S-phase in Coprinus lagopus occurs before the onset of karyogamy. It takes 8 h under the control conditions (25 °C with a 16 h light-8 h dark regime) but only 6 h under the arrest-release conditions. An important discovery in this study is that the initiation of premeiotic DNA replication is subject to an arrest by restrictive conditions (35 °C under a continuous light regime) whereas that of the mitotic replication is not. Once initiated, meiotic DNA replication can continue even under the restrictive conditions. Incorporation of “P into DNA at pachytene is quite extensive. These replications are considered to be repair replications.
Cell surface lipids and adhesion: II. the turnover of lipid components of the plasmalemma in relation to cell adhesion
Authors: Curtis A. S. G. , Shaw F. M. , Spires V. M. C. 
Published: April 2021

ABSTRACT
The preceding paper showed that those conditions that ought to stimulate reacylation of lysolipids in cells can increase cell adhesion. Similarly we found that conditions that would be expected to lead to the accumulation of lysolipids in the cell surface diminish cell adhesion. This paper reports on the answers to the following questions.
Is reacylation of lysolipids in the cells stimulated by an external supply of CoA, ATP and a fatty acid ? Does this reacylation lead to the incorporation of exogenous fatty acid in the plasmalemma ? What range of fatty acids can be incorporated into the plasmalemma and into what compounds? Does the plasmalemma contain the enzyme systems to effect this turnover, namely phospholipase A,, a CoA-ligase and an appropriate acyl transferase(s) ? Do lysolipids accumulate in the plasmalemma under conditions which diminish cell adhesion ?
We find that saturated fatty acids in the range C14–C18 and some unsaturated fatty acids are incorporated into the plasmalemmae of these neural retina cells. About 20 % of the plasma-lemmal content of fatty acids can be turned over in 30’. Incorporation is mainly into phosphatidyl choline, serine and ethanolamine in both R1 and R2 positions. The plasmalemmae contain the enzymes to effect the turnover. Isolated plasmalemmae are active in this turnover. Incubation of the plasmalemmae with phospholipase A2 leads to an accumulation of lysolipids. Very low levels of phospholipase stimulate turnover, possibly because endogenous phospholipase activity is the rate-limiting step in the system. These findings are discussed in relation to the possible mechanisms by which lipids might affect adhesion.
Appearances of microtubules after various fixative procedures, and comparison with the appearances of tobacco mosaic virus
Authors: Forer A. , Blecher S. R. 
Published: April 2021

ABSTRACT
Microtubules in crane-fly spermatids appeared altered when the glutaraldehyde-fixed cells were not postfixed with osmium tetroxide. The cytoplasmic microtubules were altered more than the doublet microtubules. Addition of osmium tetroxide after dehydration did not produce appearances identical with those of microtubules postfixed directly after glutaraldehyde, and thus at least some alterations occurred during dehydration, possibly due to extraction of microtubule-associated lipid. The omission of osmium tetroxide postfixation did not cause drastic alterations in the appearances of either tobacco mosaic virus (TMV), or polymerized tobacco mosaic virus protein (without RNA), suggesting that microtubule stability is different from TMV stability (with respect to the embedment procedure). The electron-dense stain associated with embedded–sectioned TMV is predominantly outside the TMV protein, as demonstrated by the known distribution of TMV protein compared with the dimensions of sectioned TMV and negatively stained TMV. The same might hold true for microtubules, as evidenced by the dimensions of negatively stained, isolated brain microtubules compared with those of embedded and sectioned brain microtubules.
Light-microscopic observations of individual microtubules reconstituted from brain tubulin
Authors: Kuriyama Ryoko , Miki-Noumura Taiko 
Published: April 2021

ABSTRACT
The course of polymerization of individual brain microtubules could be observed with a light microscope employing dark-field illumination. Statistical analysis of the increase in microtubule length during the polymerization was in accordance with the time course of viscosity change of the tubulin solution. After a plateau level in viscosity was attained, there was no significant change in histograms showing length distribution. These observations were confirmed with fixed and stained microtubules, using a phase-contrast microscope.
Observations with dark-field illumination revealed that reconstituted microtubules depolymerized and disappeared immediately upon exposure to buffer containing CaCl2 or sulphydryl reagents such as p-chloromercuriphenyl sulphonic acid (PCMPS) and p -chloromercuribenzoic acid (PCMB). They were also cold-labile. The growth of heterogeneous microtubules which were assembled by mixing purified tubulin dimers with ciliary outer fibres could also be followed with these optical systems.
Intranuclear electrophoresis of the chromatin of living cells
Authors: Skaer R. J. , Whytock Susan , Emmines J. P. 
Published: April 2021

ABSTRACT
Intranuclear electrophoresis of living cells under appropriate conditions causes the chromatin and nucleoli to move rapidly into the anodal side of the nucleus. In pig kidney cells, chromatin lengths attached to the nuclear envelope are oriented by the current and freed from surrounding non-oriented chromatin. Individual chromatin strands isolated in this way are often long and have not been subjected to the trauma of isolation from the nucleus. This has allowed us to demonstrate oriented lines of up to 8 chromomeres in a strand, linked by fine single fibres. These chromomeres of chromatin have the same linear dimensions as the bands and interbands of polytene chromosomes. A very wide range of morphology of chromatin is revealed — from lines of nucleosomes in open array, to strands uniformly 25 nm thick. Doublet strands and multiple strands — often embedded in darkly staining material — are also seen. All morphological types may be seen in the same nucleus. Many of the oriented threads appear to be transcriptionally active. The variable morphology of these sites and their relation to peripheral heterochromatin is discussed. Histone nucleosomes are present in these apparently transcriptionally active regions. The method is useful for investigating the relationships between chromatin and the nuclear envelope. Approximately 1500 attachment sites per nucleus are found in these cells. Some nucleoli are attached to the nuclear envelope.
Amino acid metabolism of myeloma cells in culture
Authors: Roberts R. S. , Hsu H. W. , Lin K. D. , Yang T. J. 
Published: April 2021

ABSTRACT
The growth of myeloma cells in Leibovitz medium supplemented with 20% serum was limited by the depletion of glutamine. A simple modification of the Leibovitz medium by increasing the concentrations of glutamine, lysine, isoleucine, leucine, sodium pyruvate, galactose, and vitamins resulted in over 10o% increase in cell growth yield. The total myeloma protein produced by the cells was increased by approximately 90% in modified Leibovitz media. Analysis of spent culture media for 19 amino acids showed that the concentrations of 8 amino acids were reduced; those of 5 amino acids were increased and the other 6 did not change significantly.
Classification of loops of lampbrush chromosomes according to the arrangement of transcriptional complexes
Authors: Scheer U. , Franke W. W. , Trendelenburg M. F. , Spring H. 
Published: April 2021

ABSTRACT
The arrangement of transcriptional units in the loops of lampbrush chromosomes from oocyte nuclei of urodele amphibia and from primary nuclei of the green alga Acetabularia have been studied in the electron microscope using spread preparations. Loops with different patterns of arrangement of matrix units (i.e. to a first approximation, transcriptional units) can be distinguished: (i) loops consisting of one active transcriptional unit; (ii) loops containing one active transcriptional unit plus additional fibril-free, i.e. apparently untranscribed, intercepts that may include ‘spacer’ regions; (iii) loops containing two or more transcriptional units arranged in identical or changing polarities, with or without interspersed apparent spacer regions. Morphological details of the transcriptional complexes are described. The observations are not compatible with the concept that one loop reflects one and only one transcriptional unit but, rather, lead to a classification of loop types according to the arrangement of their transcriptional units. We propose that the lampbrush chromosome loop can represent a unit for the coordinate transcription of either one gene or a set of several (different) genes.
Proportional regulation of body form and cortical organelle pattern in the ciliate Dileptus
Authors: Golinska Krystyna , Kink Jolanta 
Published: April 2021

ABSTRACT
Morphometric and ultrastructural studies of shape and pattern regulation were performed on Dileptus anser. In this cihate 2 body regions can be distinguished: proboscis and trunk. When a large portion of the trunk is excised, shape regulation occurs and the proper proboscis/trunk ratio is restored through elongation of the remnant of the trunk and shortening of the proboscis. When there is nothing but proboscis left, the trunk is formed from the proximal portion of proboscis and again the right proportion is restored.
Regulation of the ciliary pattern is based mainly on resorption of some ciliary elements. The resorption of somatic ciliature is especially intense within narrowing regions, where otherwise overcrowding of cilia would occur. The resorption of oral ciliature was found to occur within an area located at the apex of the proboscis. Oral structures when damaged by cutting may be repaired in situ. Changes in the microfibrillar system of the cell were found during regulation of shape of the posterior region of the cell, as well as during regulation of size of oral structures.
Regulatory processes in Dileptus are compared to those known for other ciliates, and possible differences between the regulation of shape and the regulation of pattern are discussed.
Extensive pairing of the xy bivalent in mouse spermatocytes as visualized by whole-mount electron microscopy
Authors: Tres Laura L. 
Published: April 2021

ABSTRACT
Autosomes and sex chromosomes of mouse spermatocytes were examined during zygotene, pachytene, and diplotene by a whole-mount electron-microscope technique after cell dispersion in a detergent solution (Nonidet-P40). Zygotene, pachytene, and diplotene stages can be adequately identified in the preparations. Thus, asynchronous side-by-side pairing of homologous autosomes, some of them displaying attached nucleoli, defines zygotene. Pachytene is identified by complete pairing of homologues. Diplotene is characterized by disjunction of bivalents (autosomes and sex chromosomes), lack of autosomal-attached nucleoli, divergent expansions observed at lateral element endings of disassembled synaptonemal complexes, end-to-end association of the XY pair and well defined outward deformations (‘bulges’) along sex chromosomal axial cores. X and Y chromosomes display at pachytene an extensive side-by-side pairing segment which decreases in length as meiotic prophase advances. Each sex chromosomal axial core appears double and is formed by close apposition of 2 nearly parallel elements displayed separately along the entire length of the chromosomal core. This double structural feature suggests that each sex chromosomal axial core is presumably composed of 2 chromatid axial cores, each of which, in turn, constitutes the respective lateral elements of short synaptonemal complexes observed at the unpaired segment.