Myosin crossbridge orientation in demembranated muscle fibres studied by birefringence and X-ray diffraction measurements

Muscle contraction is generally thought to involve changes in the orientation of myosin crossbridges during their ATP-driven cyclical interaction with actin. We have investigated crossbridge orientation in equilibrium states of the crossbridge cycle in demembranated fibres of frog and rabbit muscle, using a novel combination of techniques: birefringence and X-ray diffraction. Muscle birefringence is sensitive to both crossbridge orientation and the transverse spacing of the contractile filament lattice. The latter was determined from the equatorial X-ray diffraction pattern, allowing accurate characterization of the orientation component of birefringence changes. We found that this component decreased when relaxed muscle fibres were put into rigor at rest length, and when either the ionic strength or temperature of relaxed fibres was lowered. In each case the birefringence decrease was accompanied by an increase in the intensity of the (1,1) equatorial X-ray reflection relative to that of the (1,0) reflection. When fibres that had been stretched largely to eliminate overlap between actin- and myosin-containing filaments were put into rigor, there was no change in the orientation component of the birefringence. When isolated myosin subfragment-1 was bound to these rigor fibres, the orientation component of the birefringence increased. The birefringence changes at rest length are likely to be due to changes in the orientation of myosin crossbridges, and in particular of the globular head region of the myosin molecules. In relaxed fibres from rabbit muscle, at 100 mM ionic strength, 15 degrees C, the long axis of the heads appears to be relatively well aligned with the filament axis. When fibres are put into rigor, or the temperature or ionic strength is lowered, the degree of alignment decreases and there is a transfer of crossbridge mass towards the actin-containing filaments.     

Changes in the molecular orientation and tensile properties of uniaxially drawn cellulose films

Cellulose films were prepared by dissolving lyocell fibers in LiCl/N,N-dimethylacetamide solvent and subsequently coagulating and drying them under ambient conditions. To introduce preferred orientation, the films were uniaxially drawn under air-dry and rewetted conditions, respectively. Preferred orientation was determined by birefringence measurements and by wide-angle X-ray scattering. Mechanical properties were characterized by means of tensile tests with films conditioned to standard temperatures and humidity. Drawing resulted in the substantial reorientation of cellulose, whereby the molecular chains in the amorphous regions exhibited clearly stronger reorientation than the crystalline fraction. The average degree of orientation was comparable to orientation achieved in spun cellulose fibers. Wet-drawing resulted in improved tensile strength and modulus of elasticity but reduced elongation at break. The mechanical properties of wet-drawn films are competitive with regard to cellophane and melt-blown cellulose films, particularly considering their high modulus of elasticity of up to 26 GPa, which is also comparable to values obtained for industrially produced cellulose fibers.     

Laccase-mediated system pretreatment to enhance the effect of hydrogen peroxide bleaching of cotton fabric

This study evaluates the bleaching efficiency of the hydrogen peroxide bleaching process combined with laccase-mediated system pretreatment (LMS-HPBP) in the treatment of scoured cotton fabric. By changing the factors of laccase-mediated system pretreatment and the hydrogen peroxide bleaching process and examining the subsequent whiteness value and retained tensile strength of the samples, we find three LMS-HPBP processes that are more environment friendly than the conventional hydrogen peroxide bleaching process (CHPBP): (i) bleaching with lower dosage of hydrogen peroxide; (ii) bleaching at reduced temperature; (iii) bleaching for shortened duration. Whiteness, retained tensile strength and K/S values of cotton fabric samples treated by i-iii processes were similar to or higher than those by CHPBP. X-ray diffraction (XRD) analysis also demonstrated that the three processes rendered fabric of both lower crystallinity and bigger crystallite size than those by CHPBP. In addition, the "green" short-flow process was developed to treat cotton fabric and the results obtained shows this method is feasible as a new energy-saving process.     

Effect of orientation on the physical properties of potato amylose and high-amylose corn starch films

The effect of orientation on the properties of amylose and starch films was studied in order to determine if film strength, flexibility, and water resistance could be improved. Potato amylose and high (70%) amylose corn starch were peracetylated, cast into films, stretched in hot glycerol 1-6 times the original length, and deacetylated. Molecular orientation of potato amylose films was much higher than for high-amylose corn starch films as determined by optical birefringence. For potato amylose films, orientation resulted in large increases in tensile strength and elongation but little change in modulus. For high-amylose corn starch films, tensile strength and modulus did not change with draw ratio but elongation to break increased from about 8% to 27% as draw ratio increased from 1 to 5. Scanning electron micrographs revealed many small crazes in the drawn starch films, suggesting that the improved film toughness was due to energy dissipation during deformation of the crazes. Annealing of drawn films at 100% humidity resulted in partial crystallization and improved wet strength.     

Opto-mechanical characterization of sclera by polarization sensitive optical coherence tomography

Polarization sensitive optical coherence tomography (PSOCT) is an interferometric technique sensitive to birefringence. Since mechanical loading alters the orientation of birefringent collagen fibrils, we asked if PSOCT can be used to measure local mechanical properties of sclera.Infrared (1300 nm) PSOCT was performed during uniaxial tensile loading of fresh scleral specimens of rabbits, cows, and humans from limbal, equatorial, and peripapillary regions. Specimens from 8 human eyes were obtained. Specimens were stretched to failure at 0.01 mm/s constant rate under physiological conditions of temperature and humidity while birefringence was computed every 117 ms from cross-sectional PSOCT. Birefringence modulus (BM) was defined as the rate of birefringence change with strain, and tensile modulus (TM) as the rate of stress change between 0 and 9% strain.In cow and rabbit, BM and TM were positively correlated with slopes of 0.17 and 0.10 GPa, and with correlation coefficients 0.63 and 0.64 (P < 0.05), respectively, following stress-optic coefficients 4.69, and 4.20 GPa⁻¹. In human sclera, BM and TM were also positively correlated with slopes of 0.24 GPa for the limbal, 0.26 GPa for the equatorial, and 0.31 GPa for the peripapillary regions. Pearson correlation coefficients were significant at 0.51, 0.58, and 0.69 for each region, respectively (<0.001). Mean BM decreased proportionately to TM from the limbal to equatorial to peripapillary regions, as stress-optic coefficients were estimated as 2.19, 2.42, and 4.59 GPa⁻¹, respectively.Since birefringence and tensile elastic moduli correlate differently in cow, rabbit, and various regions of human sclera, it might be possible to mechanically characterize the sclera in vivo using PSOCT.     

Identification of hub genes through co-expression network of major QTLs of fiber length and strength traits in multiple RIL populations of cotton

The present study demonstrated a de novo correlation among fiber quality genes in multiple RIL populations including sGK9708 × 0–153, LMY22 × LY343 and Lumianyan28 × Xinluzao24. The current study was conducted to identify the major common QTLs including fiber length and strength, and to identify the co-expression networks of fiber length and strength QTLs harbored genes to target the hub genes. The RNA-seq data of sGK9708 × 0–153 population highlighted 50 and 48 candidate genes of fiber length and fiber strength QTLs. A total of 29 and 21 hub genes were identified in fiber length and strength co-expression network modules. The absolute values of correlation coefficient close to 1 resulted highly positive correlation among hub genes. Results also suggested that the gene correlation significantly influence the gene expression at different fiber development stages. These results might provide useful reference for further experiments in multiple RIL populations and suggest potential candidate genes for functional studies in cotton.     

Nanostructure and elastic modulus of single trabecula in bovine cancellous bone

We aimed to investigate the elastic modulus of trabeculae using tensile tests and assess the effects of nanostructure at the hydroxyapatite (HAp) crystal scale on the elastic modulus. In the experiments, 18 trabeculae that were at least 3 mm in length in the proximal epiphysis of three adult bovine femurs were used. Tensile tests were conducted using a small tensile testing device coupled with microscopy under air-dried condition. The c-axis orientation of HAp crystals and the degree of orientation were measured by X-ray diffraction. To observe the deformation behavior of HAp crystals under tensile loading, the same tensile tests were conducted in X-ray diffraction measurements. The mineral content of specimens was evaluated using energy dispersive X-ray spectrometry. The elastic modulus of a single trabecula varied from 4.5 to 23.6 GPa, and the average was 11.5±5.0 GPa. The c-axis of HAp crystals was aligned with the trabecular axis and the crystals were lineally deformed under tensile loading. The ratio of the HAp crystal strain to the tissue strain (strain ratio) had a significant correlation with the elastic modulus (r=0.79; P<0.001). However, the mineral content and the degree of orientation did not vary widely and did not correlate with the elastic modulus in this study. It suggests that the strain ratio may represent the nanostructure of a single trabecula and would determine the elastic modulus as well as mineral content and orientation.     

Higher order structure of chromatin: influence of ionic strength and proteolytic digestion on the birefringence properties of polynucleosomal fibers

Effects of ionic strength and proteolytic digestion on the conformation of chromatin fibers were studied by electric birefringence and relaxation measurements. The results confirm that at low ionic strength chromatin presents structural features reflecting those observed in the presence of cations. Soluble chromatin prepared from rat liver nuclei by brief nuclease digestion exhibits a positive birefringence. As the salt concentration is increased, the transition to a compact solenoidal structure is deduced from changes in electro-optical properties: the positive birefringence gradually decreases and the observed reduction in 40 mM NaCl is nearly 95%; the relaxation time decreases dramatically and the character of the kinetic changes since the decay of birefringence described initially by a spectrum of relaxation times becomes monoexponential. On digestion with proteases at low ionic strength we observe at first a rapid increase of the positive birefringence concomitant with an increase of the relaxation time. Then the birefringence decreases and becomes negative. Chromatin undergoes two successive transitions: the first transition is explained by a lengthening of nucleosomal chains without modification of the orientation of nucleosomes within the superstructure and the second one by the unwinding of the DNA tails and internucleosomal segments. When chromatin is digested at 30 mM NaCl we find a single unfolding transition characterized by the decrease of birefringence and a slight increase in the relaxation time. The results imply that the positive birefringence of chromatin does not depend on the presence of whole histone H1 and that a salt concentration of 30 mM NaCl is sufficient to modify the initial site or/and the effects of proteolytic attack.     

Endosymbionts: factors on egg pattern formation

Elimination of the intracellular symbionts of Euscelis plebejus either by X-ray irradiation of the posterior pole of the freshly laid egg or by interruption of egg infection by application of tetracycline or lysozyme to female leafhoppers leads to the production of embryos without abdomens, ‘head-embryos’.Homogenates of symbiont-free eggs and symbiont-containing eggs in the state of invagination have a pH of 7·5±0·2 and 7·0±0·2 and an osmotic pressure (pO) of 8·3±0·2 and 7·8±0·2, respectively. The presence of symbionts leads to a decrease of both the pH and pO.These data indicate that the correct formation of the posterior gradient, necessary for normal abdomen development, is dependent on the presence of endosymbionts at the posterior pole. It is possible that the symbionts change the pH and pO of the posterior gradient. These results are consistent with a hypothetical model of early differentiation of the Euscelis egg.     

Lactic acid bacteria: hydrophobicity and strength of attachment to meat surfaces

The hydrophobicity and strength of a ttachment of several lactic acid bacteria with antimicrobial activity were studied. Hydrophobicity was determined by bacterial adherence to hydrocarbons (BATH; octane or xylene), adhesion to nitrocellulose filters (NCF), salt aggregation test (SAT) and adherence to phenyl–Sepharose beads (PSB). The relative hydrophobicity of lactic acid bacteria depended markedly on the method used. No correlation between either SAT or BATH (octane) and strength of attachment (Sr value) existed. However, a significant relationship between strength of attachment and BATH (xylene), NCF and PSB, respectively, was observed, showing the highest correlation coefficient ( r = 0·778) for BATH (xylene).     

The relative effects of collagen fiber orientation, porosity, density, and mineralization on bone strength

This investigation determined the relative importance of collagen fiber orientation, porosity, density, and mineralization in determining the tensile strength of bovine cortical bone. Thirty-nine specimens were tested for failure stress and the values of eight histologic and compositional parameters: collagen fiber orientation, wet and dry apparent density, percent mineralization of the bone matrix, and several components of porosity (Haversian canals, Volkmann's canals, and plexiform vascular spaces). Linear regression analysis showed that collagen fiber orientation was consistently the single best predictor of strength. Mineralization of the bone matrix was generally a poor predictor of strength. Density and porosity ranked between these variables in importance. Multiple regression equations containing all significantly correlated variables achieved correlation coefficients of 0.607 for plexiform bone and 0.881 for osteonal bone. Also, separate analysis of plexiform and osteonal specimens showed that the latter group was weaker even though it was less porous, apparently because it had collagen fibers which were less longitudinally oriented. This study suggests it is feasible to develop better empirical formulae for the prediction of cortical bone strength than are currently available if a variety of variables is introduced. Additional data are needed to confirm these results.     

氮素对不同开花期棉铃纤维比强度形成的生理基础的影响

于2005年在江苏南京(长江流域下游棉区)和徐州(黄河流域黄淮棉区)棉田设置不同氮素水平(零氮：0 kg N·hm^-2,适氮：240 kg N·hm^-2,高氮：480 kg N·hm^-2)试验,研究氮素对不同开花期棉铃(伏前桃、伏桃和秋桃)纤维比强度形成生理基础的影响.结果表明：与适氮处理相比,零氮处理显著降低了棉铃对位叶氮浓度,增加了C/N,影响程度随开花期的推迟而加大,导致伏桃、秋桃对位叶制造和运输光合产物的能力在棉铃发育中后期大幅度下降,棉纤维的相对生长速率以及纤维发育关键酶蔗糖合成酶和β-1,3-葡聚糖酶活性降低,纤维素快速累积持续期缩短,纤维比强度显著降低;高氮处理显著增加了棉铃对位叶氮浓度,降低了C/N,影响程度随开花期的推迟而降低,其降低了伏前桃、伏桃发育过程中光合产物向纤维分配的比例、棉铃发育前中期的纤维发育关键酶活性及纤维素累积速率,导致其纤维比强度亦显著降低.综合分析认为,适宜的施氮量可以协调棉花的“源库”关系,有利于促进不同开花期棉铃高纤维比强度的形成.与适氮处理相比,零氮处理的伏前桃、伏桃和秋桃纤维比强度分别降低了1.8%、5.8%和13.0%,高氮处理则分别降低了8.2%、7.4%和-2.4%.     

Microbial cellulolytic activity of the brackish water in the Tvärminne area,Northern Baltic Sea

Microbial cellulolytic activity was determined by an indirect method (loss of tensile strength in cotton yarn). The activity values were high in late autumn, but low in spring and early summer. The factors responsible for the seasonal variation are discussed.     

The Effects of Cell Cycle Parameters on Cell Wall Regeneration and Cell Division of Cotton Protoplasts (Gossypium hirsutum L.)

Protoplasts of cotton cotyledons were isolated and culturedto undergo cell wall regeneration and cell division. DNA contentand cell cycle parameters of nuclei from cotyledons and/or protoplastswere determined by flow cytometry. The DNA content of cotton,Gossypium hirsutum L., was estimated to be 4·34±0·12pg DNA per nucleus. There was a strong positive correlation between G₂ or Sand G₂,and cell wall regeneration and cell division and a strong negativecorrelation between G₁, and cell wall regeneration and celldivision of cotton cotyledon protoplasts. The cell cycle statusof cotyledons changes during their development; as the cotyledonsenlarge, the proportion of cells in G₀ and G₁ phases of thecell cycle increases. The implication of these results in relationto protoplast growth and development is discussed. Key words: Cell cycle parameters, cell wall regeneration, cell division, flow cytometry, Gossypium     

Effect of treatment with very dilute acids on the wet tensile strength and chemical properties of paper

Filter paper (α-cellulose content 99·3%) was soaked in very dilute solutions of several mineral and aliphatic dicarboxylic acids and heated for various times at temperatures ranging from 100°C to 140°C. The wet strength of the paper, measured with an Instron tester using a jaw span of 15 cm, was greatly increased by these treatments. The largest increase was by nearly 1000%; this was achieved by heating with oxalic acid at pH 2·7 for 1 h at 140°C. Increases of nearly 750% and 850% were obtained with hydrochloric and sulphuric acids, respectively, under similar conditions. Homologues of oxalic acid, which were too weak to furnish solutions of pH 2·7, caused only small increases in wet strength.The increases in wet strength have been attributed to the formation of inter-fibre cross-links. A small loss of dry strength was observed and this, together with increases in copper number and fluidity, was taken as evidence that some hydrolytic degradation occurred simultaneously with cross-linking. Short-span breaking-load tests also confirmed this conclusion. The zero-span breaking load, which is a measure of the strength of the fibres rather than of the paper itself, fell markedly as a result of the acid treatments. However, as the span was increased the breaking load of the treated paper levelled out at a finite value whereas that of the untreated paper fell close to zero.The nature of the cross-links was studied by chemical tests. The effect of chlorous acid and borohydride treatment on the tensile strength of the acid-treated paper showed that a small proportion of the cross-links were hemiacetals. However, the main proportion appeared to be ethers. This was demonstrated by measuring the effects of the acid treatments on the proportions of ‘available’ primary and secondary hydroxyl groups by tosylation followed by iodination.     

Electric properties of macromolecules. IX. Dipole moment, polarizability, and optical anisotropy factor of collagen in solution from electric birefringence

The electric birefringence of collagen solutions has been measured over a wide range of field strength with the pulse technique. The soluble collagen was from rat tail tendon. The solvent used was dilute acetic acid. Very pronounced saturation of the electric birefringence was observed, permitting calculation of the optical anisotropy factor. The Kerr constant was determined by extrapolation to zero field strength. From the dependence on field strength of the birefringence, the permanent dipole moment and the anisotropy of polarizability were separately determined. The contribution of the former to the Kerr constant was found to be twice as large as that of the latter. The same conclusion was obtained from the initial slope of the rise curves of the birefringence at low fields. The permanent dipole moment was 1.5 × 10⁴ Debye, and the anisotropy of polarizability was about 3 × 10^?15 cm.³. The magnitude of the latter indicates that the ion atmosphere polarization is important. Effects of added salt and thermal denaturation on the electric birefringence were explored.     

DNA polymorphism: spectroscopic and electro-optic characterizations of Z-DNA and other types of left-handed helical structures induced by Ni2+

CD and uv spectroscopy reveal that the synthetic polynucleotides poly(dG–dC) · poly(dG–dC) and poly(dG–m⁵dC) · poly(dG–m⁵dC) undergo a transition induced by small amounts of Ni⁺⁺ cation from a right-handed B-form to left-handed Z-type conformations. We describe the application of steady-state and transient electric birefringence to the characterization of the transition observed at very low ionic strength (10 mM Tris HCl, pH 7.4). Dialysis experiments show that the changes in spectroscopic and electro-optic properties upon addition of Ni⁺⁺ are completely reversible. The differences in shape of the inverted CD spectra suggest the existence of a family of left-handed conformations, depending on the polymer used and on the amounts of cation added. The stoichiometry required for inducing the Z-conformation of poly(dG–m⁵dC) is 1 cation/4 nucleotide phosphates. The transition is accompanied by a decrease in birefringence, an increase in length, and the more important contribution of a permanent or slowly induced dipole moment to the orientation mechanism. High concentrations of Ni⁺⁺ promote the Z → Z* transition. Upon increasing the Ni⁺⁺ concentration, poly(dG–dC) undergoes a biphasic transition, first to one intermediate conformation that is neither B- nor Z-like and then to a left-handed form that is probably different from Z*. These conversions are accompanied by regular decreases both in birefringence and in chain length, but no transient appears in the field-reversal experiments.     

The effects of orientation and location on the strength of dorsal rat skin in high and low speed tensile failure experiments

The tensile strength of skin is associated, in part, with its potential for laceration from impact. The quasi-static tensile strength of skin depends on orientation. The objective of this study was to determine whether the strength of skin in high speed tensile failure experiments exhibits a similar dependence on orientation. Tensile experiments were conducted at 6000 percent/s and 30 percent/s on dorsal skin of rats aged 1-6 months. Experiments were performed on specimens cut perpendicularly and longitudinally to the spine at cranial and caudal locations. The tensile failure properties depended on location, orientation, age and strain rate. The strength was dependent on orientation to the same degree in high and low speed tests. This helps explain why accident statistics show that skin lacerates preferentially on the body.     

The chemical composition and energy contents of copepods and cladocerans in relation to their size

The chemical composition and energy contents of four different species of cladocerans, one species of a calenoid copepod, and mixed samples of four species of cyclopoid copepods were quantitatively determined. The relative chemical composition, expressed as a percentage of the total organic matter (excluding chitin) of each of the different species analysed, were very similar. The mean relative composition for all species was 71·2% protein, 9·5% carbohydrates, 19·3% lipids, 16·5% total nitrogen and 2·1% total phosphate–phosphorus. A substantial amount of the total nitrogen was found to be non-protein nitrogen (mean of 23·3% of total nitrogen). The calorific value was calculated from the estimated amounts of proteins, carbohydrates and lipids using conversion factors. The relationship between the calculated organic matter and the chemical oxygen demand (COD) was found to be constant and did not vary much for the different species. The ratio of total organic matter to COD has a mean value of 0·51. Calorific values ranged from 5847 to 6353 cal/g total organic matter. The amounts of chemical substances or energy contents per individual Copepoda or Cladocera were calculated. Regression lines together with their correlation coefficients have been computed to describe the relationship between the amount of chemical constituents and energy contents per individual, and the length of the individual. The results are extensively compared with those given in the literature and differences are discussed.     

Biological efficiency and nutritive value of Pleurotus sajor-caju cultivated on different agro-wastes

The oyster mushroom, Pleurotus sajor-caju (Fr.) Singer, was cultivated on a number of agro-residues and their mixtures. Biological efficiency, defined as the percentage conversion of substrate into fruit bodies on a dry weight basis, was found to be maximum on paddy straw supplemented with cotton seeds (12·82 g/100 g substrate). Biochemical changes effected in the substrates as a result of mushroom growth, in terms of nitrogen content and degradation of cellulose, hemicellulose and lignin components, were monitored. The proximate compositions of fruit bodies of the mushroom in terms of protein, total carbohydrates, fat, fibre and ash were determined. The crude protein and total carbohydrate contents varied from 26·3% to 36·7% and 41·2% to 47·1%, respectively, on various residues. The variation in the contents of crude fat, crude fibre and ash ranged from 1·7% to 2·0%, 11·7% to 17·0% and 6·1%, respectively, on different residues. The energy value of the fruit bodies was found to be between 275 and 300 kCal/100 g, whereas the energy recovery of the substrate in the fruit bodies was from 5% to 10%.