Arrangement Of Cellulose Microfibrils Research Articles

Hydration-induced reversible deformation of the pine cone

The scales of pine cones undergo reversible deformation due to hydration changes in order to optimize seed dispersal. This improves the survivability of the pine. The reversible flexing of the scales is caused by two tissue layers arranged in a sandwich configuration: a layer composed of sclereid cells and a sclerenchyma layer. They expand differentially upon hydration (and contract upon dehydration) due to differences in the structure that are analyzed here for Torrey pine (Pinustorreyana) cones. In addition to this well-known mechanism by which the cellulose microfibrils in the scales vary their angle with the wood cell axis, we confirm the presence of a porosity gradient in the sclereid cells and calculate, using a model consisting of three layers, the stresses generated upon dehydration taking into account the effect of hydration on the elastic modulus. Our quantitative analysis reveals that this gradient structure can significantly decrease the stress concentrations due to the mismatch between the two layers, and show that this is an ingenious design to increase the interfacial toughness to improve the robustness of pine cone scales. We also show that each individual layer of sclereid cells and sclerenchyma fibers undergoes bending when hydrated separately, and suggest that the two layers operate synergistically to effect the required deformation for seed release. A synthetic bioinspired analog consisting of hydrogels with different porosities is used to confirm this principal actuation mechanism. These findings may inspire the materials science and mechanical engineering communities to develop more robust, biocompatible and energy-efficient actuation systems. Statement of significanceSome biological structures can exhibit reversible deformation enabled by water inflow and outflow of their structure. We analyse the reversible motion of pine cone scales. The dehydration produces their flexure and opening, resulting in the release of seeds and their dispersal, when conditions are right. This process is reversible, and rehydration of the pine cone recloses the scales. The processes of flexing and straightening are governed by shrinking and swelling which are directed by differences in the arrangement of cellulose microfibrils in a bilayer construct. We demonstrate that the scales are more complex than a simple bilayer structure and that they actually have gradients, which significantly reduce the internal stresses and ensure their integrity. We analyse the process of opening and closing of the scales for a gradient structure in the Torrey pine cone using a simple idealized trilayer model. The results demonstrate a significant decrease in internal stresses produced by the gradient structure. Using the lessons learned from the pine cone, we produce a bilayer junction using hydrogels with different porosities which exhibit the same reversible bending response.

Fibrous matrix component of cell wall in the giant-celled green alga Valonia utricularis observed by atomic force microscopy in liquid.

The cell walls of the giant-celled green alga Valonia exhibit the "crossed-fibril" arrangement of cellulose microfibrils (CMFs). The existence of fibrous matrix components coiling around the CMFs was recently reported using atomic force microscopy (AFM). To understand the biological role of this fibrous wall component, we attempted to reveal the detailed morphology of the fibrous structure of the cell walls isolated from V. utricularis specimens in artificial seawater (ASW), by using an improved method of AFM. We also investigated the effect of incubation in an acidic environment that had been known to make the cell walls liable to separate into layers, on the morphology of the fibrous structures. Thin, fibrous structures were found to entangle around a single CMF or multiple adjacent CMFs, the thickness of which was 0.85nm on average. Incubation in acidic ASW (pH4), greatly modified the morphology of the fibrous structures in quality and quantity, compared with those incubated in the original ASW (pH8). Thickness of the fibrous structures was increased to 4.63nm on average, remarkable deformations were observed, and the density of the structures was reduced to less than half by incubation in the acidic ASW. In addition, same fibrous structures extended over CMFs and forming aggregates were observed on the surface of the cell wall layers separated artificially. Fluorescence microscopy of cell walls treated with Vicia villosa lectin conjugated with fluorescein isothiocyanate showed specific labelling of cell wall regions where the fibrous structures were present abundantly as observed by AFM. From these observations, it can be assumed that the fibrous structures of V. utricularis are the matrix component of the cell wall containing N-acetylgalactosamine, involved in the maintenance of the cell wall integrity through bonding the neighboring cell wall layers, and their morphology and function of V. utricularis are sensitive to acidic pH.

In Silico Comparison of the Hemicelluloses Xyloglucan and Glucuronoarabinoxylan in Protecting Cellulose from Degradation

We used a previously developed simulation model of a plant cell wall and its enzymatic degradation to compare the abilities of two hemicelluloses, glucuronoarabinoxylan (GAX) and xyloglucan (XG), to protect cellulose microfibrils (CMFs) from attack by cellulose-degrading enzymes. Additionally, we investigated the effect of XG abundance on the degradation rate of CMFs in the presence of the same enzymes. Simulations were run using hypothetical cell-wall compositions in which the numbers and arrangement of CMFs and (1,3;1,4)-β-glucan were kept constant, but the proportions of GAX and XG were altered. Scenarios considered walls with low and equal proportions of either GAX or XG, and also low, medium and high proportions of XG in the absence of GAX. The rate of CMF degradation was much lower in walls with GAX than walls with XG, except for early in the simulation when the reverse held, suggesting that XGs were protecting CMFs by competitive inhibition. Increasing XG content reduced both the degradation rate of CMFs and the percent of XG degraded, indicating that activity of enzymes decreased with XG density despite XG being degradable. Glucose oligosaccharide breakdown products were analysed on the basis of the originating polysaccharide and their degree of polymerisation (DP). The presence of GAX as opposed to equal amounts of XG had some significant effects on the amount and profile of breakdown products from XG and CMFs.

Xylem Development and Cell Wall Changes of Soybean Seedlings Grown in Space

Plants growing in altered gravity conditions encounter changes in vascular development and cell wall deposition. The aim of this study was to investigate xylem anatomy and arrangement of cellulose microfibrils in vessel walls of different organs of soybean seedlings grown in Space. Seeds germinated and seedlings grew for 5 d in Space during the Foton-M2 mission. The environmental conditions, other than gravity, of the ground control repeated those experienced in orbit. The seedlings developed in space were compared with those of the control test on the basis of numerous anatomical and ultrastructural parameters such as number of veins, size and shape of vessel lumens, thickness of cell walls and deposition of cellulose microfibrils. Observations made with light, fluorescence and transmission electron microscopy, together with the quantification of the structural features through digital image analysis, showed that the alterations due to microgravity do not occur at the same level in the various organs of soybean seedlings. The modifications induced by microgravity or by the indirect effect of space-flight conditions, became conspicuous only in developing vessels at the ultrastructural level. The results suggested that the orientation of microfibrils and their assembly in developing vessels are perturbed by microgravity at the beginning of wall deposition, while they are still able to orient and arrange in thicker and ordered structures at later stages of secondary wall deposition. The process of proper cell-wall building, although not prevented, is perturbed in Space at the early stage of development. This would explain the almost unaltered anatomy of mature structures, accompanied by a slower growth observed in seedlings grown in Space than on Earth.

Arrangement of cellulose microfibrils in the wheat straw cell wall

The arrangement of cellulose microfibrils in the cell wall from different tissues of wheat straw was investigated mainly using atomic force microscope (AFM). It was revealed that cellulose microfibrillar crystals arrange randomly in the parenchyma cell walls and are ordered quite well longitudinal to the fiber axis in the epidermal fibers. The microfibrillar crystals are about 20 nm in diameter and 150–200 nm in length. Moreover, the cellulose microfibrillar crystals in the epidermal fibers align periodically along the fiber axis and the periodicity is similar to the length of the fibrillar crystals. This structure was confirmed by small angle X-ray scattering (SAXS).

Distinct fluorescent pattern of KAT1::GFP in the plasma membrane of Vicia faba guard cells

The organisation of membrane proteins into certain domains of the plasma membrane (PM) has been proposed to be important for signalling in yeast and animal cells. Here we describe the formation of a very distinct pattern of the K + channel KAT1 fused to the green fluorescent protein (KAT1::GFP) when transiently expressed in guard cells of Vicia faba. Using confocal laser scanning microscopy we observed a radially striped pattern of KAT1::GFP fluorescence in the PM in about 70% of all transfected guard cells. This characteristic pattern was found to be cell type and protein specific and independent of the stomatal aperture and the cytoskeleton. Staining of the cell wall of guard cells with Calcofluor White revealed a great similarity between the arrangement of cellulose microfibrils and the KAT1::GFP pattern. Furthermore, the radial pattern of KAT1::GFP immediately disappeared when turgor pressure was strongly decreased by changing from hypotonic to hypertonic conditions. The pattern reappeared within 15 min upon reestablishment of high turgor pressure in hypotonic solution. Evaluation of the staining pattern by a mathematical algorithm further confirmed this reversible abolishment of the radial pattern during hypertonic treatment. We therefore conclude that the radial organisation of KAT1::GFP depends on the close contact between the PM and cell wall in turgid guard cells. These results offer the first indication for a role of the cell wall in the localisation of ion channels. We propose a model in which KAT1 is located in the cellulose fibrils intermediate areas of the PM and discuss the physiological role of this phenomenon.

Research note: Deposition patterns of cellulose microfibrils in flange wall ingrowths of transfer cells indicate clear parallels with those of secondary wall thickenings.

The arrangement of cellulose microfibrils and cortical microtubules in transfer cells depositing flange wall ingrowths have been determined with field emission scanning electron microscopy and immunofluorescence confocal microscopy. In xylem transfer cells of wheat (Triticum aestivum) stem nodes and transfer cells of corn (Zea mays) endosperm tissue, cellulose microfibrils were aligned in parallel bundles to form the linear wall ingrowths characteristic of flange ingrowth morphology. In both cell types, linear bundles of cellulose microfibrils were deposited over an underlying wall composed of randomly arranged microfibrils. Acid extraction of wheat xylem transfer cells established that flange ingrowths were composed of crystalline cellulose. Immunofluorescence labelling of microtubules in wheat xylem transfer cells showed that bundles of microtubules were positioned directly below and parallel with developing flange ingrowths, whereas more mature ingrowths were flanked by bundles of microtubules. These results show that the parallel organisation of cellulose microfibrils in flange wall ingrowths is similar to those in secondary wall thickenings in xylem elements, and that deposition of these structures in transfer cells is also likely to involve bundling of parallel arrays of microtubules. Our observations are discussed in terms of the possible role of microtubules in building flange-type wall ingrowths and the consequences in terms of predicted mechanisms required to build the fundamentally different reticulate-type wall ingrowths.

Cellulose synthesizing terminal complexes in the ascidians

The structure of cellulose synthesizing terminal complexes (TCs) has been investigated in different species of ascidians. The linear-shaped TCs consisting of two types of membrane particles were found in four species belonging to two orders including previous data . A relationship between the length of TCs and the size of produced cellulose microfibrils was found within the same order. The density and localization patterns of TCs coincided with the arrangement of cellulose microfibrils in the innermost layer of the tunic, that is outer protective tissue and a major cellulosic component in the ascidians. This suggests that the shape and dimension of the microfibril bundle is influenced by an arrangement of TCs in the epidermal cell membrane.

Ultrastructure of the S2 layer in relation to lignin distribution inPinus radiata tracheids

The ultrastructure of the S2 layer in relation to its lignin distribution was examined using transmission electron microscopy in the tracheids ofPinus radiata. The S2 layer had a striated appearance at low magnification. Observations at higher magnifications showed lignin to be distributed inhomogeneously in this layer, appearing as a mosaic of electron-dense and electron-lucent regions. These regions are scattered, showing a pattern of often interconnecting sinuous features in a predominantly radial profile. The significance of these features of the S2 layer is discussed, particularly in relation to the available information from recent ultrastructural observations on the appearance of cellulose microfibrils and the pattern of their distribution in the S2 layer using rapid freeze-deep etching in conjunction with transmission electron microscopy. Predictions are made as to the likely distribution and arrangement of cellulose microfibrils in the S2 layer based on the pattern of lignin distribution observed in this layer.

Regulation of directional expansion by the cortical microtubule array in roots of Lemna minor.

We reported previously that uniconazole, an inhibitor of gibberellin biosynthesis, does not induce lateral swelling of root in Lemna minor L. This is inconsistent with previous reports that gibberellin inhibitors induce significant lateral swelling of organs in other plants. The present study aims to elucidate the reason for this inconsistency. We assayed cells of the cortex, which occupy a large part of root volume. Treatment with propyzamide, a microtubule-disrupting agent, induced increases in root diameter due to increases in radial and tangential diameters of cells in all tissues, particularly the cortex. Additionally, cortical microtubules of cortical cells were almost removed, and the orientation of cellulose microfibrils became random. Thus, in the root cortex, cortical microtubules regulate orientation of cellulose microfibrils. When plants were cultured in the presence of uniconazole the diameter of roots decreased, mainly due to decreases in cell width in the middle layer of cortex. Arrangement of cellulose microfibrils of cortical cells remained transverse after uniconazole treatment. Although cortical microtubules were fragmented by uniconazole treatment, they also remained arranged in the transverse direction. It seems that fragmented but transversely arranged cortical microtubules can orient cellulose microfibrils transversely.

Arrangement of cortical microtubules in the shoot apex of Vinca major L.

The arrangements of cortical microtubules (MTs) and of cellulose microfibrils in the median longitudinal cryosections of the vegetative shoot apex of Vinca major L., were examined by immunofluorescence microscopy and polarizing microscopy, respectively. The arrangement of MTs was different in the various regions of the apex: the MTs tended to be arranged anticlinally in tunica cells, randomly in corpus cells, and transversely in cells of the rib meristem. However, in the inner layers of the tunica in the flank region of the apex, cells with periclinal, oblique or random arrangements of MTs were also observed. In leaf primordia, MTs were arranged anticlinally in cells of the superficial layers and almost randomly in the inner cells. Polarizing microscopy of cell walls showed that the arrangement of cellulose microfibrils was anticlinal in tunica cells, random in corpus cells, and transverse in cells of the rib meristem; thus, the patterns of arrangement of microfibrils were the same as those of MTs in the respective regions. These results indicate that the different patterns of arrangement of MTs and microfibrils result in specific patterns of expansion in the three regions. These differences may be necessary to maintain the organization of the tissues in the shoot apex.

THE HELICOIDAL CELL WALL AS A TIME REGISTER.

Helicoidal cell walls are characterized by an oscillatory shift in the arrangement of cellulose microfibrils somewhat reminiscent of the rotating movement of the hands of a clock. The periodic movement can be sustained or perturbed. Thus, the helicoidal cell wall presents a temporal reading. Sensitive to temporal signals, the cell wall keeps a record of cellular events and registers very small variations, storing data at a subcellular level. The present paper emphasizes some aspects of the helicoidal cell wall relevant to timekeeping, revealing its dynamics and flexibility and leading to the question of the mechanisms of its construction. Contents I. Summary 345 II. Introduction 345 III. Levels of timekeeping structures 346 IV. From watch to wall 347 V. Internal and external alterations 351 VI. Conclusions 353 References 354.

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.