Evidence for the Regulation of the Shift in Cellulose Microfibril Orientation in Freeze-Fractured Plasma Membrane of Boergesenia forbesii

Morphological evidence regarding the regulation of the directionof movement of the cellulose-synthesizing complexes in Boergeseniawas obtained by observing the distribution of intramembranousparticles (IMPS) around the complexes. In complexes with straightconfigurations, the distribution of IMPS on both sides of thecomplexes was almost equal. In complexes characterized by acurved configuration, however, the IMPS density was greaterin the outer half-circle of the curve. Some particles on thisside were attached to or intruded into the complex, and theirsizes were no different from those of the IMPS on the fracturedplane. These results indicate that the distribution and orientationof the particles in relation to the complex have been affectedby membrane fluidity and, that membrane fluidity might playa key role in determining the regulation of the direction ofmovement of the complex. (Received July 16, 1984; Accepted October 12, 1984)     

Cellulose Microfibril Orientation in Rubbery Wood

The fibre length L and average helical angle of microfibrilorientation in fibres from successive growth rings in both normaland ‘rubbery’ wood of stems of apple var. Lord Lambournehave been measured. It has been shown that the normal relationship,L = A+B cot , does not hold for ‘rubbery wood’.There is a tendency for the helix to remain flat, the angle fairly constant independently of fibre length. This, togetherwith abnormalities in the lignin chemistry, causes the rubberywood to have low tensile strength and high extensibility.     

Effects of Blue Light on Cell Elongation and Microtubule Orientation in Dark-Grown Gametophytes of Ceratopteris richardii

Gametophytes of Ceratopteris richardii developed into strap-shapedprothalli in the dark. The prothalli had an apical meristem,a subapical elongation zone and a basal zone where no growthoccurred. Continuous irradiation of blue light inhibited cellgrowth of the elongation zone, although red or far-red lighthad no effect on elongation. Cortical microtubules (MTs) ofsubapical cells reoriented from transverse to oblique or parallelto the growing axis during blue light inhibition. Each regionof the strap-shaped prothallus was irradiated with a micro-beamof blue light. Cell elongation in the subapical region was notinhibited by irradiation at the apical meristem. Irradiationof the subapical region inhibited cell elongation to a similarextent as the whole irradiation control. When a single elongatingcell at one side of the subapical region was irradiated by ablue microbeam, elongation was inhibited in a cell at the irradiateside only, resulting in a bowing prothallus. Cortical MTs reorientedfrom transverse to longitudinal to the cell axis in irradiatedcells only. The results indicate that each cell in the subapicalregion perceives blue light by itself, reorients only its corticalMTs and ceases only its cell elongation, independent of surroundingcells. (Received October 17, 1996; Accepted December 9, 1996)     

Modification in Cell Shape Unrelated to Cellulose Microfibril Orientation in Growing Thallus Cells of Chaetomorpha moniligera

Cellulose microfibril orientation patterns in thallus cellsof Chaetomorpha moniligera were studied, and the relationshipbetween the microfibril and the peripheral microtubule arrangementsduring cell-shape modification by colchicine was examined. Inthe cuttings from growing thalli, linearly arranged cylindricalcells developed into cask-shaped cells during 4–6 daysof culture at 27?C. In the cylindrical cells, microfibrils formingthe innermost portion of the wall were arranged alternatelyin longitudinal and transverse directions, but peripheral microtubuleswere always arranged only in a longitudinal direction. Thesefeatures were also noted in the cask-shaped cells. Colchicineat 10^–3M and 3?10^–3M accelerated both cell expansionand wall thickening with matrix deposition, but the directionsin which both microfibrils and microtubules were arranged werethe same as those of the cylindrical cells. These results indicatethat (1) the microfibril and microtubule arrangements of Chaetomorphaare not necessarily correlated, (2) changes in cell shape ofChaetomorpha are not necessarily accompanied by changes in thearrangement of cell-wall microfibrils, and (3) colchicine playsa role in the loosening and thickening of cell walls by enhancingmatrix deposition. (Received June 2, 1986; Accepted February 13, 1987)     

Xyloglucan Endotransglycosylase Activity, Microfibril Orientation and the Profiles of Cell Wall Properties Along Growing Regions of Maize Roots

A series of physical and chemical analyses were made on theexpanding zone of maize seedling roots grown in hydroponics.Comparison of longitudinal profiles of local relative elementalgrowth rate and turgor pressure indicated that cell walls becomelooser in the apical 5 mm and then tighten 5–10 mm fromthe root tip. Immersion of roots in 200 mol m^–3 mannitol(an osmotic stress of 0·48 MPa) rapidly and evenly reducedturgor pressure along the whole growing region. Growth was reducedto a greater extent in the region 5–10 mm from the roottip than in the apical region. This indicated rapid wall-looseningin the root tip, but not in the more basal regions. Following 24 h immersion in 400 mol m^–3 mannitol (an osmoticstress of 0·96 MPa) turgor had recovered to pre-stressedvalues. Under this stress treatment, growth was reduced in theregion 4–10 mm from the root tip, despite the recoveryof turgor, indicating a tightening of the wall. In the rootapex, local relative elemental growth rate was unchanged incomparison to control tissue, showing that wall properties herewere similar to the control values. Cellulose microfibrils on the inner face of cortical cell wallsbecame increasingly more parallel to the root axis along thegrowth profile of both unstressed and stressed roots. Orientationdid not correlate with the wall loosening in the apical regionof unstressed roots, or with the tightening in the region 5–10mm from the root tip following 24 h of osmotic stress. Longitudinal profiles of the possible wall-loosening enzymexyloglucan endotransglycosylase (XET) had good correspondencewith an increase in wall loosening during development. In thezone of wall tightening following osmotic stress, XET activitywas decreased per unit dry weight (compared with the unstressedcontrol), but not per unit fresh weight. Key words: Osmotic stress, turgor, growth, cell wall properties, microfibrils, XET     

Effects of Inhibitors of Myosin Light Chain Kinase and Other Protein Kinases on the First Cell Division of Sea Urchin Eggs

We investigated effects of protein kinase inhibitors on the first cell division in sea urchin eggs on the assumption that phosphorylation of myosin is requisite for the formation and/or the contraction of the contractile ring. ML-7 or ML-9, which inhibits myosin light chain kinase (MLCK), inhibited cytokinesis with a half maximal inhibition at 0.1–0.2 mM. The nuclear division was accomplished normally at 0.2–0.25 mM where the cytokinesis was completely blocked. Fluorescent staining of actin filaments with rhodamine-labeled phalloidin revealed that the contractile ring was not formed in the cleavage-inhibited eggs. H-7 which inhibits cAMP-dependent protein kinase, cGMP-dependent protein kinase and protein kinase C arrested the process of the division at mid-cleavage at 0.25–0.3 mM and at metaphase or anaphase at 0.5 mM. H-8 and HA1004, which inhibit cAMP-dependent and cGMP-dependent protein kinases did not show significant effect at millimolar order. In the presence of micromolar concentrations of staurosporine which preferentially inhibits protein kinase C and MLCK small mitotic apparatuses were formed, in which chromosomes did not form the metaphase plate. The role of phosphorylation in the cell division is discussed.     

Growth and phototropic bending in Boergesenia rhizoid

The rhizoid of Boergesenia forbesii. a coenocytic green alga,exhibited typical tip growth. The growth stopped at temperatureslower than 15?C and was promoted by red light but inhibitedby blue light (430 nm). The rhizoid showed negative phototropicbending caused by blue light, and the mode of bending was the"bulging" type. The dioptric effect was not involved in thisnegative phototropism. The phototropicbending process was modifiedgreatly by temperature. At low temperature (18?C), bending didnot occur but the phototropic effect could be accumulated andstored. The accumulated effect appeared as a bending in thedark when the temperature was raisedto 25?C. This accumulatedphototropic effect, designated "stored bending", attenuatedat a half-life of 1.5 hr at 18?C in the dark. (Received February 24, 1979; )     

Microfibrillar structure of growing cell wall in a coenocytic green alga,Boergesenia forbesii

A fine structure of cell wall lamellae in a coenocytic green algaBoergesenia forbesii was examined by electron microscopy. The wall has a polylamellate structure containing cellulose microfibrils 25 to 30 nm in diameter. The outer surface of the cell was covered by a thin structureless lamella, underneath which existed a lamella containing randomly-oriented microfibrils. The major part of the wall consisted of two types of lamellae, multifibrillar lamella and a transitional, matrix-rich one. In the former, microfibrils were densely arranged more or less parallel with each other. In the transitional lamella, existing between the multifibrillar ones, the microfibril orientation shifted about 30° within the layer. The fibril orientation also shifted 30° between adjacent transitional and multifibrillar layers, and consequently the microfibril orientation in the neighboring multifibrillar layers shifted 90°. It was concluded that the orientation rotated counterclockwise when observed from inside the cell. Each lamella in the thallus wall become thinner with cell expansion, but no reorientation of microfibrils in the outer old layers was observed. In the rhizoid, the outer lamellae sloughed off with the tip growth.     

Inductive and Inhibitory Effects of Light on Cell Division in Chattonella antiqua

The cell division of a red tide flagellate, Chattonella antiqua,was synchronously induced under light and dark regimes of 10L14D(a light period, L, for 10 h followed by a dark period, D, for14 h), 12L12D and l4L10D. In all regimes cell number began toincrease ca. 14 h after the onset of L and almost doubled duringone LD cycle. When the light-off timing of the last L was changedor the whole L was shifted, cells that had been synchronizedunder 12L12D invariably began to divide ca. 14 h after the onsetof L. This shows that the timing of cell division was determinedby the time of the onset of L. When cells were continuously exposed to light after a cell division,the subsequent cell division was inhibited. This effect waslimited to cells that had been synchronized under short-dayconditions. Thus it can be concluded that light has both inductive and inhibitoryeffects on cell division in this alga, the latter effect dependingupon the previously given light and dark regimes. (Received December 21, 1984; Accepted February 28, 1985)     

Microfibril orientation across the secondary cell wall of Radiata pine tracheids

Polarised light microscopy and transmission electron microscopy were used to measure the variation in cellulose microfibril orientation across the secondary cell wall of Pinus radiata D. Don tracheids using oblique sections. Variations in orientation for the S1, S2 and S3 layers were determined for radial and tangential cell walls from the juvenile and mature earlywood at the base of the stem and at 5 m height. Microfibrils in the S1 layer are usually arranged in an S-helix (>90°) varying from 79° to 117° among tracheids. Within individual tracheids the microfibril orientation in the S1 region can be quite variable, sometimes changing from an S to Z-helix but without a well-defined crossed structure. Microfibrils in the S2 layer form a Z-helix (<90°) with average orientation varying from 1° to 59° among tracheids, while the S3 layer is also often a Z-helix varying from 50° to113° in orientation. The S2 layer shows significant variation among sample points within the tree related to age and height, while the S1 and S3 layers show small random variations within the tree. Microfibril orientation in the S2 layer is very uniform, although when variation does occur the trend is exclusively for an increase towards the S1 region. Orientation in the S3 layer often varies continuously from the S2 boundary to the lumen. The S3 layer becomes much thinner with increasing age and height, making measurement by light microscopy more difficult. The innermost lamellae of microfibrils at the lumen surface sometimes show a distinctive clustering, forming macrofibrils of varying orientation but this may be the result of delignification treatment.     

Orientation of Wall Microfibril Deposition in Root Cells of Pisum sativum L. var Alaska

The arrangement of wall microfibrils on the inner surface ofcortical cells in pea roots was observed by a replica method.In the elongating region, microfibrils were deposited transverselyto the root axis. After cell elongation stopped, the orientationof microfibril deposition changed discontinuously from a transverseto an oblique one. The change occurred at 6–7 mm fromthe root tip. The oblique orientation seemed to change discontinuouslyto another oblique one as time passed. (Received January 24, 1986; Accepted May 15, 1986)     

Diversity of Cellulose Microfibril Arrangement in the Cell Walls of Lygeum spartum Leaves

Extraction of matrix material, cytochemical methods and stereoanalysiswere used to study cell-wall architecture in leaves of Lygeumspartum, a grass species growing in sub-and regions of the Mediterraneanzone Most tissues were lignified with the exception of mesophyllcells Better results were obtained with NaOH extraction thanwith methylamine extraction The different types of fibres (sub-epidermal,axial and bundle sheath fibres), parenchyma and epidermal cellswere characterized by specific cell-wall organization The differentwall textures were variations of the basic helicoidal model Lygeum spartum L, lignified leaf fibres, cell wall, helicoidal texture, polysaccharide cytochemistry     

Effects of Light and Inhibitors of Photosynthesis and Respiration on the Multiplication of Tobacco Mosaic Virus in Tobacco Protoplasts

The multiplication rate of tobacco mosaic virus (TMV) in tobaccoprotoplasts in light was several times than in the dark. 3-(3,4-Dichlorophenyl)-1,1-dimethylurea(DCMU) at 10^–5M completely antagonized this illuminationeffect. KCN at 10^–4 M and antimycin A at 10^–5 M,which prevented the protoplasts from surviving in the dark,did not block TMV multiplication in light. Inhibitor experimentsshowed that photosynthesis and respiration were indirectly associatedwith the TMV multiplication. Either of them was found to benecessary for TMV multiplication but neither was indispensable.They play complementary roles in the supply of energy and materialsrequired for virus production. (Received August 2, 1984; Accepted July 9, 1985)     

Action spectrum of negative phototropism in Boergesenia forbesii

The rhizoid of Boergesenia forbesii, a gigantic unicellulargreen alga, exhibited negative phototropism. The bending processat 32?C followed Weber-Fechner's law and Bunsen- Roscoe's law.The minimum light energy inducing the phototropic bending was30 J.m^–2 at 467 nm and 32?C. The action spectrum of thisnegative phototropism had two distinct peaks at 380 and 443nm, with shoulders at 430 and 470 nm and a trough around 410run. Light of wavelengths longer than 502 nm was ineffective.The structure of the spectrum agrees well with that reportedfor the positive phototropism of Avena coleoptiles and otherplant parts. (Received February 24, 1979; )     

Computational Design of TrkB Peptide Inhibitors and Their Biological Effects on Ovarian Cancer Cell Lines

There are large numbers of different intracellular signaling pathways regulated by Tyrosine kinases (Trk) receptors. Trk receptors, especially TrkB, are also frequently overexpressed in a variety of human malignant tumors. In this study, we have computationally designed small peptide-based inhibitors of TrkB and investigated their effects on the proliferation and apoptosis of two ovarian cancer cell lines. Molecular docking of TrkB with its ligand and antagonist, BDNF and Cyclotraxin B respectively, was carried out using HADDOCK program. A peptide library was constructed based on the critical residues involved in the TrkB binding site. After docking and optimization, two selected peptides were purchased and their effects on the viability and apoptosis of the cells were evaluated by performing MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) test and flow cytometry assay. Subsequently, the levels of expression and phosphorylation statues of TrkB and its two downstream genes including MAPK3 and eIF4E were assessed with western blot. We found that designed peptides effectively reduced TrkB, MAPK3 and eIF4E phosphorylation, reduced cell viability and induced apoptosis in the treated cells when compared to untreated cells. In conclusion, the BDNF/TrkB signaling is shown to be attenuated substantially in the presence of peptide inhibitors suggesting a strong inhibitory potential of the designed peptides for Trk family.     

肌球蛋白轻链激酶及其抑制剂

肌球蛋白轻链激酶（ＭＬＣＫ）是三磷酸肌醇（ＩＰ３）、Ｃａ２＋－钙调蛋白（ＣａＭ）信息转导途径的一种重要蛋白质，也是第一个被发现的依赖于ＣａＭ的激酶，对肌肉收缩起着重要作用［１］。ＭＬＣＫ抑制剂从ＣａＭ水平或ＭＬＣＫ自身水平上抑制ＭＬＣＫ的活性，可抑制或减弱平滑肌的收缩。天然植物中的多种化合物对ＭＬＣＫ有较强的抑制作用，有吖啶类、黄酮类、蒽醌类、菲类和喹啉类化合物等，为植物资源的开发利用提供了有价值的依据。１．ＭＬＣＫ的结构和酶促反应动力学研究ＭＬＣＫ的活性型是由Ｃａ２＋、ＣａＭ和全酶组成的三元复…     

Cell cycle analysis in a multinucleate green alga,Boergesenia forbesii (Siphonocladales,Chlorophyta)*

The cell cycle (nuclear division cycle) of a multinucleate green alga, Boergesenia forbesii (Harvey) Feldmann was studied using microspectrophotometry and BrdU incorporation techniques. Mitosis was observed frequently 1-4 h after the beginning of the light period, on a 16:8 h LD cycle at 25°C. Mitotic nuclei formed discrete patches. Other nuclei remained in the G₁ period. The DNA synthetic phase (S phase) was estimated to last about 12 h from microspectrophotometric study using aphidicolin inhibition just before the S phase and release from it. The G₂ period was estimated to be about 2 h, because a labeled prophase nucleus could be detected when the samples were labeled with BrdU continuously over 3 h. The incorporation pattern of BrdU changed through the S phase nucleus. In early S phase, BrdU staining was detected as many dots in the entire nucleus, while in late S phase, it was detected as several discrete regions along the nuclear membrane. Almost all nuclei in B. forbesii were in the G₁ stage after nuclear division, and the nuclei in several patches of the cell simultaneously initiated DNA synthesis. Once the nuclei entered into S phase, these nuclei continued into G₂ and mitosis. In other words, the cell cycle regulation of entrance into S phase from G₁ is an important factor in the growth and morphogenesis in B. forbesii.     

Microfibril Orientation Dominates the Microelastic Properties of Human Bone Tissue at the Lamellar Length Scale

The elastic properties of bone tissue determine the biomechanical behavior of bone at the organ level. It is now widely accepted that the nanoscale structure of bone plays an important role to determine the elastic properties at the tissue level. Hence, in addition to the mineral density, the structure and organization of the mineral nanoparticles and of the collagen microfibrils appear as potential key factors governing the elasticity. Many studies exist on the role of the organization of collagen microfibril and mineral nanocrystals in strongly remodeled bone. However, there is no direct experimental proof to support the theoretical calculations. Here, we provide such evidence through a novel approach combining several high resolution imaging techniques: scanning acoustic microscopy, quantitative scanning small-Angle X-ray scattering imaging and synchrotron radiation computed microtomography. We find that the periodic modulations of elasticity across osteonal bone are essentially determined by the orientation of the mineral nanoparticles and to a lesser extent only by the particle size and density. Based on the strong correlation between the orientation of the mineral nanoparticles and the collagen molecules, we conclude that the microfibril orientation is the main determinant of the observed undulations of microelastic properties in regions of constant mineralization in osteonal lamellar bone. This multimodal approach could be applied to a much broader range of fibrous biological materials for the purpose of biomimetic technologies.