The Wood Parenchyma of Triplochiton scleroxylon K. Schum

Unusual features in the histology of the secondary xylem wererevealed during an investigation into growth-ring developmentin Triplochiton in Nigeria. The main observation was the presenceof two kinds of apotracheal parenchyma: (1) strands made uplongitudinally of 2 to 4 (occasionally more) cells containingstarch and, (2) empty fusiform strands, without cross-walls.Each kind of parenchyma formed ‘units’, i.e. uniseriatetangential rows of like strands between the wood-rays. The starchystrands (storage parenchyma) became more numerous towards theend of each growth ring.     

Functional and Biochemical Characterization of Human Eukaryotic Translation Initiation Factor 3 in Living Cells

The main role of the translation initiation factor 3 (eIF3) is to orchestrate formation of 43S-48S preinitiation complexes (PICs). Until now, most of our knowledge on eIF3 functional contribution to regulation of gene expression comes from yeast studies. Hence, here we developed several novel in vivo assays to monitor the integrity of the 13-subunit human eIF3 complex, defects in assembly of 43S PICs, efficiency of mRNA recruitment, and postassembly events such as AUG recognition. We knocked down expression of the PCI domain-containing eIF3c and eIF3a subunits and of eIF3j in human HeLa and HEK293 cells and analyzed the functional consequences. Whereas eIF3j downregulation had barely any effect and eIF3a knockdown disintegrated the entire eIF3 complex, eIF3c knockdown produced a separate assembly of the a, b, g, and i subunits (closely resembling the yeast evolutionary conserved eIF3 core), which preserved relatively high 40S binding affinity and an ability to promote mRNA recruitment to 40S subunits and displayed defects in AUG recognition. Both eIF3c and eIF3a knockdowns also severely reduced protein but not mRNA levels of many other eIF3 subunits and indeed shut off translation. We propose that eIF3a and eIF3c control abundance and assembly of the entire eIF3 and thus represent its crucial scaffolding elements critically required for formation of PICs.     

Comparative Structure of Companion Cells and Phloem Parenchyma Cells in Mimosa pudica L.

The phloem of Mimosa pudica L. furnishes an example of definablediversification of the parenchymatic members of the tissue intocompanion cells and parenchyma cells. The companion cells havedense protoplasts which contain the typical organelles of plantcells, including chloroplasts and many ribosomes. The sieveelements and companion cells are interconnected by numerousbranched plasmodesmata. The companion cells degenerate whenthe associated sieve elements cease to function. The parenchymacells have less dense protoplasts than the companion cells.In many parenchyma cells the rough endoplasmic reticulum assumesa tubular form, and bundles of microfilaments are present. Thecytoplasmic ribosomes occur in groups apparently held togetherby fibrils. Chloroplasts, mitochondria (some are exceptionallylong), dictyosomes, microbodies, and microtubules are the othercell components. Whether the parenchyma cells are ontogeneticallyrelated to the sieve elements or not, they do not degeneratewhen the sieve element ceases to function.     

Fast Label-Free Cytoskeletal Network Imaging in Living Mammalian Cells

We present a full-field technique that allows label-free cytoskeletal network imaging inside living cells. This noninvasive technique allows monitoring of the cytoskeleton dynamics as well as interactions between the latter and organelles on any timescale. It is based on high-resolution quantitative phase imaging (modified Quadriwave lateral shearing interferometry) and can be directly implemented using any optical microscope without modification. We demonstrate the capability of our setup on fixed and living Chinese hamster ovary cells, showing the cytoskeleton dynamics in lamellipodia during protrusion and mitochondria displacement along the cytoskeletal network. In addition, using the quantitative function of the technique, along with simulation tools, we determined the refractive index of a single tubulin microtubule to be n_tubu = 2.36 ± 0.6 at λ = 527 nm.The cytoskeleton is mainly composed of an actin and tubulin microtubule network, and it has many important roles at the cellular scale (1). It allows the cell to modify its shape, is implied in cell migration and adhesion processes, and is used as a support for organelle displacement inside cells.Optical microscopy is useful for dynamic studies in which the cytoskeletal network is reorganizing quickly. However, due to the poor native interaction between light and this network fluorescence labeling is commonly used to image the cytoskeleton (2). Anisotropic approaches are also used on this kind of structure, as the cytoskeletal filaments may present refractive index anisotropy. Based on this property, polarized microscopy has been used to reveal the cytoskeleton (3). However, this technique is relatively slow compared to the cytoskeleton dynamics and requires perfectly stressless optics and a nondepolarizing sample. Differential interference contrast (DIC) approaches enhance the contrast in unstained cytoskeletal fibers (4) but also require precise light polarization control of both samples and optical components (for example, no plastic elements can be used for standard DIC). Moreover, the image has a gradient shape that induces loss of resolution and makes the images hard to interpret, especially in complex biological environments. Some DIC-based developments have been proposed that would make it possible to retrieve quantitative information from the sample and/or minimize the effects of depolarizing elements (5–8). Nonlinear interactions in second-harmonic generation (SHG) (9) that are sensitive to orientation and anisotropic refractive index are also applied to cytoskeleton imaging. Label-free imaging is thus obtained, but it requires a powerful laser and a scanning approach that may be too slow when fast dynamics need to be studied.Although light interaction with a nonlabeled cytoskeleton is weak, with barely any absorption, there is a signature on the beam that travels through the structure even with nonpolarized illumination/detection. Indeed, as tubulin microtubules and actin filaments are denser than the cytoplasm, their respective refractive indices are also higher (10). This means that the light is slightly delayed by the cytoskeleton, leading to a possible contrast when looking at the phase component of light. In this article, we consider quantitative phase microscopy (QPM) based on quadriwave lateral shearing interferometry (QWLSI) (11). QWLSI makes it possible to image nonlabeled cells with a conventional transillumination microscope equipped with a halogen lamp. We propose a modified version of the QWLSI presented in our previous publication (11) that allows the fast, sensitive, and highly resolved imaging required to reveal cytoskeletal network dynamics in living cells. After discussing the signal/noise ratio (SNR) of our approach, we compare QPM with immunostaining of actin and tubulin microtubules on Chinese hamster ovary (CHO) cells, demonstrating the capability of QPM to visualize the cytoskeleton. Living wild-type (wt) CHO cells are then imaged at a high frame rate (2.5 Hz) to illustrate the spatiotemporal resolution of the technique for cytoskeleton imaging.     

Fast Label-Free Cytoskeletal Network Imaging in Living Mammalian Cells

We present a full-field technique that allows label-free cytoskeletal network imaging inside living cells. This noninvasive technique allows monitoring of the cytoskeleton dynamics as well as interactions between the latter and organelles on any timescale. It is based on high-resolution quantitative phase imaging (modified Quadriwave lateral shearing interferometry) and can be directly implemented using any optical microscope without modification. We demonstrate the capability of our setup on fixed and living Chinese hamster ovary cells, showing the cytoskeleton dynamics in lamellipodia during protrusion and mitochondria displacement along the cytoskeletal network. In addition, using the quantitative function of the technique, along with simulation tools, we determined the refractive index of a single tubulin microtubule to be n_tubu=2.36±0.6$n_{tubu}=2.36\pm 0.6$ at λ=527$\lambda =527$ nm.     

四合木属四合木(蒺藜科)的木材解剖学研究

在光学显微镜和扫描电子显微镜下观察了蒺藜科四合木属四合木(Tetraena mongolica Maim.)木材结构.其导管分子直径小,管壁厚,分布密度高,分子短,端壁几乎水平,具单穿孔;管间纹孔为对列或互列的具缘纹孔;韧性纤维短、壁厚、壁上有较少的单纹孔;同型单列射线、分布密度高;轴向薄壁组织散生或傍导管生.这些表明四合木的木材解剖特征是与干旱环境条件是相适应的.     

The Differentiation of Contact Cells and Isolation Cells in the Xylem Ray Parenchyma of Populus maximowiczii

A histochemical analysis was made of the differentiation ofcontact cells and isolation cells in the xylem ray parenchymaof Populus maximowiczii. The contact cells formed secondarywalls at approximately the same time as adjoining vessel elements.The lignification of the cell walls of contact cells and vesselelements began earlier than that of wood fibres and isolationcells. Thus, the formation of the secondary wall, includinglignification, of the contact cells might occur at the sametime as that of the vessel elements to which they are directlyconnected. By contrast, the isolation cells began to form secondarywalls later than the vessel elements and wood fibres in thevicinity of the isolation cells. After the deposition of thesecondary wall, a protective layer was formed in contact cellsbut no isotropic layer was observed in isolation cells. Theresults suggest the importance of vessel elements in the determinationof the differentiation of adjoining ray parenchyma cells.Copyright1999 Annals of Botany Company Contact cell, isolation cell, vessel element, xylem differentiation, Populus maximowiczii Henry.     

Arrangement of Cellulose Microfibrils in Walls of Elongating Parenchyma Cells

The arrangement of cellulose microfibrils in walls of elongating parenchyma cells of Avena coleoptiles, onion roots, and celery petioles was studied in polarizing and electron microscopes by examining whole cell walls and sections. Walls of these cells consist firstly of regions containing the primary pit fields and composed of microfibrils oriented predominantly transversely. The transverse microfibrils show a progressive disorientation from the inside to the outside of the wall which is consistent with the multinet model of wall growth. Between the pit-field regions and running the length of the cells are ribs composed of longitudinally oriented microfibrils. Two types of rib have been found at all stages of cell elongation. In some regions, the wall appears to consist entirely of longitudinal microfibrils so that the rib forms an integral part of the wall. At the edges of such ribs the microfibrils can be seen to change direction from longitudinal in the rib to transverse in the pit-field region. Often, however, the rib appears to consist of an extra separate layer of longitudinal microfibrils outside a continuous wall of transverse microfibrils. These ribs are quite distinct from secondary wall, which consists of longitudinal microfibrils deposited within the primary wall after elongation has ceased. It is evident that the arrangement of cellulose microfibrils in a primary wall can be complex and is probably an expression of specific cellular differentiation.     

Readily Accessible Multiplane Microscopy: 3D Tracking the HIV‐1 Genome in Living Cells

Human immunodeficiency virus (HIV)‐1 infection and the associated disease AIDS are a major cause of human death worldwide with no vaccine or cure available. The trafficking of HIV‐1 RNAs from sites of synthesis in the nucleus, through the cytoplasm, to sites of assembly at the plasma membrane are critical steps in HIV‐1 viral replication, but are not well characterized. Here we present a broadly accessible microscopy method that captures multiple focal planes simultaneously, which allows us to image the trafficking of HIV‐1 genomic RNAs with high precision. This method utilizes a customization of a commercial multichannel emission splitter that enables high‐resolution 3D imaging with single‐macromolecule sensitivity. We show with high temporal and spatial resolution that HIV‐1 genomic RNAs are most mobile in the cytosol, and undergo confined mobility at sites along the nuclear envelope and in the nucleus and nucleolus. These provide important insights regarding the mechanism by which the HIV‐1 RNA genome is transported to the sites of assembly of nascent virions.      

Functional Anatomy of the Heart of Reptiles

Intravascular pressures, distributions of blood oxygen, dye-dilutioncurves, cineradiography, and electromagnetic flowmeters in majorvessels suggest a highly directional flow oE systemic and pulmonaryvenous blood through reptilian hearts. The lacertilian rightaortic arch contains blood from the pulmonary, and the leftfrom the pulmonary or sometimes both pulmonary and systemicveins. Traces made of the pressure and blood flow show thatthe lacertilian and chelonian cava venosum and pulmonale arefunctionally distinct. Atrioventricular valves probably preventregurgitation during ventricular systole and form an obstructionbetween the cava arteriosum and venosum during ventricular filling.The muscular ridge approaches the ventral ventricular wall atsystole forming a functional ventricular septum. Low pulmonaryvascular resistance favors pulmonary ejection before systemic.In Pseudemys the balance between pulmonary and systemic resistancecauses a left-to-right shunt during respiration and a right-to-leftshunt during diving; the latter probably reduces the expenditureof cardiac energy during hypoxia. Pressure traces and cineradiographyindicate separation of systemic and pulmonary venous returnsin alligators. The left ventricle perfuses both aortic archesand the right the pulmonary arch. Right ventricular pressuremay exceed pulmonary pressure during ejection suggesting animpedance in the pulmonary outflow tract. Pulmonary resistancein crocodilians may increase during diving, instituting a right-to-leftshunt.     

Contributions to the Wood Anatomy of the Rubioideae (Rubiaceae)

Damnacanthus , Lasianthus, Saldinia, and Trichostachys are also included. Wood anatomical characters are compared with recent phylogenetic insights into the study group on the basis of molecular data. The observations demonstrate that the delimitation and separation of several taxa from the former Coussareeae/Morindeae/Prismatomerideae/Psychotrieae aggregate is supported by wood anatomical data. The Coussareeae can be distinguished from the other Rubioideae by their scanty parenchyma, septate libriform fibres, and the combination of uniseriate and very high multiseriate rays with sheath cells. Axial parenchyma bands and fibre-tracheids characterise Gynochtodes and some species of Morinda (Morindeae s.str.), but the latter genus is variable with respect to several features (e.g. vessel groupings and axial parenchyma distribution). Wood data support separation of Rennellia and Prismatomeris from Morindeae s.str.; vessels in both genera are exclusively solitary and axial parenchyma is always diffuse to diffuse-in-aggregates. Damnacanthus differs from the Morindeae alliance by the occurrence of septate fibres, absence of axial parenchyma, and the occasional presence of fibre wall thickenings. There are interesting similarities between members of the Lasianthus clade and the Pauridiantheae/Urophyleae group such as the sporadic occurrence of spiral thickenings in axial parenchyma cells. Received 26 January 2001/ Accepted in revised form 6 June 2001     

An Overview of the Biology of Reaction Wood Formation

Reaction wood possesses altered properties and performs the function of regulating a tree＇s form, but it is a serious defect in wood utility. Trees usually develop reaction wood in response to a gravistimulus. Reaction wood in gymnosperms is referred to as compression wood and develops on the lower side of leaning stems or branches. In arboreal, dicotyledonous angiosperms, however, it is called tension wood and is formed on the upper side of the leaning. Exploring the biology of reaction wood formation is of great value for the understanding of the wood differentiation mechanisms, cambial activity, gravitropism, and the systematics and evolution of plants. After giving an outline of the variety of wood and properties of reaction wood, this review lays emphasis on various stimuli for reaction wood induction and the extensive studies carried out so far on the roles of plant hormones in reaction wood formation. Inconsistent results have been reported for the effects of plant hormones. Both auxin and ethylene regulate the formation of compression wood in gymnosperms. However, the role of ethylene may be indirect as exogenous ethylene cannot induce compression wood formation. Tension wood formation is mainly regulated by auxin and gibberellin. Interactions among hormones and other substances may play important parts in the regulation of reaction wood formation.     

Bimolecular Fluorescence Complementation; Lighting-Up Tau-Tau Interaction in Living Cells

Abnormal tau aggregation is a pathological hallmark of many neurodegenerative disorders and it is becoming apparent that soluble tau aggregates play a key role in neurodegeneration and memory impairment. Despite this pathological importance, there is currently no single method that allows monitoring soluble tau species in living cells. In this regard, we developed a cell-based sensor that visualizes tau self-assembly. By introducing bimolecular fluorescence complementation (BiFC) technique to tau, we were able to achieve spatial and temporal resolution of tau-tau interactions in a range of states, from soluble dimers to large aggregates. Under basal conditions, tau-BiFC cells exhibited little fluorescence intensity, implying that the majority of tau molecules exist as monomers. Upon chemically induced tau hyperphosphorylation, BiFC fluorescence greatly increased, indicating an increased level of tau-tau interactions. As an indicator of tau assembly, our BiFC sensor would be a useful tool for investigating tau pathology.     

Secondarily-forming Coated Vesicles in Ray Parenchyma Cells of Pinus radiata Needle Traces

Coated vesicles in ray parenchyma cells of Pinus radiata needletraces were observed to form secondarily from smooth vesicles.The nascent coated vesicles were seen as small protrusions ofthe bounding membrane of smooth vesicles. Initially they wereellipsoidal or dome shaped, later becoming spheroidal. Althougha coat was observable at the spheroidal stage the coat was mostpronounced in vesicles that had separated from parent smoothvesicles. Coated vesicles were most common near dictyosomeswhere they were often seen in stages of formation from smoothvesicles and in the cortical cytoplasm near the plasmalemma.The plasmalemma developed small protrusions some of which appearedcoated at the cytoplasmic face. Coated vesicles, Pinus radiata, needle trace, ray parenchyma     

Xylem Hydraulic Characteristics, Water Relations and Wood Anatomy of the Resurrection PlantMyrothamnus flabellifoliusWelw.

Myrothamnus flabellifoliusWelw. is a desiccation-tolerant (‘resurrection’)plant with a woody stem. Xylem vessels are narrow (14 µmmean diameter) and perforation plates are reticulate. This leadsto specific and leaf specific hydraulic conductivities thatare amongst the lowest recorded for angiosperms (k_s0.87 kg m^-1MPa^-1s^-1;k_l3.28x10^-5kg m^-1MPa^-1s^-1, stem diameter 3 mm). Hydraulic conductivitiesdecrease with increasing pressure gradient. Transpiration ratesin well watered plants were moderate to low, generating xylemwater potentials of -1 to -2 MPa. Acoustic emissions indicatedextensive cavitation events that were initiated at xylem waterpotentials of -2 to -3 MPa. The desiccation-tolerant natureof the tissue permits this species to survive this interruptionof the water supply. On rewatering the roots pressures thatwere developed were low (2.4 kPa). However capillary forceswere demonstrated to be adequate to account for the refillingof xylem vessels and re-establishment of hydraulic continuityeven when water was under a tension of -8 kPa. During dehydrationand rehydration cycles stems showed considerable shrinking andswelling. Unusual knob-like structures of unknown chemical compositionwere observed on the outer surface of xylem vessels. These maybe related to the ability of the stem to withstand the mechanicalstresses associated with this shrinkage and swelling.Copyright1998 Annals of Botany Company cavitation, desiccation, hydraulic conductivity, refilling, resurrection plant, root pressure, xylem anatomy,Myrothamnus flabellifolius