Immunolocalization and structural variations of xylan in differentiating earlywood tracheid cell walls of Cryptomeria japonica

Insights into asynchronous changes of cell wall polymers accumulated in different cell types during conifer xylem differentiation

An improved understanding of the events involved in cell wall polymers deposition during xylem development could provide new scientific ways for molecular regulation and biomass utilization. Axial and radial cells are spatially heterogeneous and have highly cross-correlated developmental behavior, whereas the deposition of corresponding cell wall polymers during xylem differentiation is less studied. To clarify our hypothesis that cell wall polymers of two cell types accumulated asynchronously, we performed hierarchical visualization, including label-free in situ spectral imaging of different polymer compositions during the development of Pinus bungeana. In axial tracheids, the deposition of cellulose and glucomannan was observed on earlier stages of secondary wall thickening than that of xylan and lignin, while xylan distribution was strongly related to spatial distribution of lignin during differentiation. The content of lignin and polysaccharides increased by over 130 % and 60 % respectively when the S₃ layer was formed, compared to the S₂ stage. In ray cells, the deposition of crystalline cellulose, xylan, and lignin was generally lagged compared to that in corresponding axial tracheids, although the process followed a similar order. The concentration of lignin and polysaccharides in ray cells was only approximately 50 % of that in the axial tracheids during secondary wall thickening.

Radial Movement of Minerals in the Trunks of Standing Japanese Cedar (Cryptomeria Japonica D. Don) Trees in Summer by Tracer Analysis

The radial movement of minerals in tree trunks is a widely accepted function of ray parenchyma cells, but there is little experimental evidence for this. We previously obtained experimental data showing that the parenchyma cells were the site of the radial mineral movement in Japanese cedar (Cryptomeria japonica D. Don) trunks in winter. Therefore, the aim of this study was to answer two remaining questions: do parenchyma cells move minerals via active transport or passive diffusion and how do seasonality and the injection duration affect the radial movement of minerals. To analyze this, we compared mineral movement in living standing Japanese cedar trees with heartwood in which the trunk had been left untreated or freeze–thawed with liquid nitrogen to kill the living cells. A solution of a stable isotope of cesium (Cs), as a tracer of mineral movement, was continuously injected into the outer sapwood of these normal and freeze–thaw-treated trees for an objective period, following which the trunk was freeze-fixed with liquid nitrogen. The Cs distribution in frozen samples was then analyzed by cryo-scanning electron microscopy/energy-dispersive X-ray spectroscopy. After 1 and 5 days of injection, the Cs detection area was almost the same among parenchyma cells and tracheid cell walls in the freeze–thaw-treated samples (without living cells) but was further toward the inner xylem in the parenchyma cells than the tracheids in the normal samples (with living cells), indicating that living parenchyma cells move Cs. Furthermore, after 5 days of injection, Cs in the tracheid cell walls was detected further toward the inner xylem in the normal samples than in the freeze–thaw-treated samples, indicating that Cs is exuded from the parenchyma cells into the tracheid cell walls. Together, these results suggest that the radial movement of minerals in standing Japanese cedar trees occurs through a combination of active transport by parenchyma cells and diffusion in the cell walls.

Artificially lignified cell wall catalyzed by peroxidase selectively localized on a network of microfibrils from cultured cells

An artificial lignified cell wall was synthesized in three steps: (1) isolation of microfibrillar network; (2) localization of peroxidase through immunoreaction; and (3) polymerization of DHP to lignify the cell wall. Artificial woody cell wall synthesis was performed following the three steps along with the actual formation in nature using cellulose microfibrils extracted from callus derived from Cryptomeria japonica. First, we constructed a polysaccharide network on a transmission electron microscopy (TEM) grid. The preparation method was optimized by chemical treatment, followed by mechanical fibrillation to create a microfibrillated network. Morphology was examined by TEM, and chemical characterization was by Fourier transform infrared (FTIR) spectroscopy. Second, we optimized the process to place peroxidase on the microfibrils via an immunoreaction technique. Using a xyloglucan antibody, we could ensure that gold particles attached to the secondary antibodies were widely and uniformly localized along with the microfibril network. Third, we applied the peroxidase attached to secondary antibodies and started to polymerize the lignin on the grid by simultaneously adding coniferyl alcohol and hydrogen peroxide. After 30 min of artificial lignification, TEM observation showed that lignin-like substances were deposited on the polysaccharide network. In addition, FTIR spectra revealed that the bands specific for lignin had increased, demonstrating the successful artificial formation of woody cell walls. This approach may be useful for studying woody cell wall formation and for producing made-to-order biomaterials.

Heterogeneous distribution of xylan and lignin in tension wood G-layers of the S1+G type in several Japanese hardwoods

A gradual shift in the microfibril angle of gelatinous layer (G-layer) of tension wood fibres of the S1+G type has been detected via potassium permanganate (KMnO4) staining. Thus, microfibril angles in fibres of the S1+G type are different from S1+S2+G type fibres. We evaluated the microfibril orientation and presence of lignin and xylan in G-layers of tension wood fibres of the S1+G type in several Japanese hardwoods. The distribution of xylan and lignin was examined using immunoelectron microscopy with anti-xylan monoclonal antibody, ultraviolet (UV) microscopy, fluorescence microscopy after acrifravine staining and transmission electron microscopy after KMnO4 staining. In transverse sections, the outer parts of the G-layers showed ultraviolet absorption and a heterogeneous KMnO4 staining pattern, suggesting that lignin was heterogeneously distributed in the outer parts of the G-layers. The heterogeneous staining pattern was found in the G-layers of several tree species; however, the degree of staining differed between tree species. In longitudinal sections, the KMnO4-staining region in the G-layers continued parallel to the cell axis to variable lengths. The orientation of cellulose microfibrils changed gradually from a steep helix to parallel to the cell axis from the outer to inner parts of the G-layers. Xylan immunolabelling was observed in the outer part of the G-layers; in some fibres, labelling was found in the innermost parts of the G-layers. Following immunogold labelling combined with KMnO4 staining, xylan labelling was mainly found in KMnO4-stained electron-opaque regions, suggesting that lignin and xylan were heterogeneously colocalized in the outer parts of the G-layers. The rotation of cellulose microfibrils and heterogeneous distribution of xylan and lignin might be a general phenomenon in S1+G tension wood fibres.

Advances in molecular engineering of carbohydrate-binding modules

Carbohydrate-binding modules (CBMs) are non-catalytic domains that are generally appended to carbohydrate-active enzymes. CBMs have a broadly conserved structure that allows recognition of a notable variety of carbohydrates, in both their soluble and insoluble forms, as well as in their alpha and beta conformations and with different types of bonds or substitutions. This versatility suggests a high functional plasticity that is not yet clearly understood, in spite of the important number of studies relating protein structure and function. Several studies have explored the flexibility of these systems by changing or improving their specificity toward substrates of interest. In this review, we examine the molecular strategies used to identify CBMs with novel or improved characteristics. The impact of the spatial arrangement of the functional amino acids of CBMs is discussed in terms of unexpected new functions that are not related to the original biological roles of the enzymes. Proteins 2017; 85:1602-1617. © 2017 Wiley Periodicals, Inc.

Plant Fibre: Molecular Structure and Biomechanical Properties, of a Complex Living Material, Influencing Its Deconstruction towards a Biobased Composite

Plant cell walls form an organic complex composite material that fulfils various functions. The hierarchical structure of this material is generated from the integration of its elementary components. This review provides an overview of wood as a composite material followed by its deconstruction into fibres that can then be incorporated into biobased composites. Firstly, the fibres are defined, and their various origins are discussed. Then, the organisation of cell walls and their components are described. The emphasis is on the molecular interactions of the cellulose microfibrils, lignin and hemicelluloses in planta. Hemicelluloses of diverse species and cell walls are described. Details of their organisation in the primary cell wall are provided, as understanding of the role of hemicellulose has recently evolved and is likely to affect our perception and future study of their secondary cell wall homologs. The importance of the presence of water on wood mechanical properties is also discussed. These sections provide the basis for understanding the molecular arrangements and interactions of the components and how they influence changes in fibre properties once isolated. A range of pulping processes can be used to individualise wood fibres, but these can cause damage to the fibres. Therefore, issues relating to fibre production are discussed along with the dispersion of wood fibres during extrusion. The final section explores various ways to improve fibres obtained from wood.

Do plant cell walls have a code?

A code is a set of rules that establish correspondence between two worlds, signs (consisting of encrypted information) and meaning (of the decrypted message). A third element, the adaptor, connects both worlds, assigning meaning to a code. We propose that a Glycomic Code exists in plant cell walls where signs are represented by monosaccharides and phenylpropanoids and meaning is cell wall architecture with its highly complex association of polymers. Cell wall biosynthetic mechanisms, structure, architecture and properties are addressed according to Code Biology perspective, focusing on how they oppose to cell wall deconstruction. Cell wall hydrolysis is mainly focused as a mechanism of decryption of the Glycomic Code. Evidence for encoded information in cell wall polymers fine structure is highlighted and the implications of the existence of the Glycomic Code are discussed. Aspects related to fine structure are responsible for polysaccharide packing and polymer-polymer interactions, affecting the final cell wall architecture. The question whether polymers assembly within a wall display similar properties as other biological macromolecules (i.e. proteins, DNA, histones) is addressed, i.e. do they display a code?

Dehydrogenative polymerization of coniferyl alcohol in artificial polysaccharides matrices: effects of xylan on the polymerization

To elucidate the influence of wood polysaccharide components on lignin formation in vitro, models for polysaccharide matrix in wood secondary cell wall were fabricated from two types of bacterial cellulosic films, flat film (FBC) and honeycomb-patterned film (HPBC), as basic frameworks by depositing xylan onto the films. An endwise type of dehydrogenative polymerization, "Zutropfverfahren", of coniferyl alcohol was attempted in the films with/without xylan. The resultant dehydrogenation polymer (DHP) was generated inside and outside xylan-deposited films, whereas DHP was deposited only outside the films without xylan. The amount of the generated DHP in the xylan-deposited films was larger than that in the films without xylan. The frequency of 8-O-4' interunitary linkage in DHP was also increased by the xylan deposition. These results suggest that xylan acts as a scaffold for DHP deposition in polysaccharides matrix and as a structure regulator for the formation of the 8-O-4' linkage. In addition, mechanical properties, i.e., tensile strength and modulus of elasticity (MOE), of both cellulosic films were found to be augmented by the deposition of xylan and DHP. Especially, DHP deposition remarkably enhanced MOE. Such effects of xylan on DHP formation and augmentation of mechanical strength were clearly observed for HPBC, revealing that HPBC is a promising framework model to investigate wood cell wall formation in vitro.

Relative deposition of xylan and 8-5'-linked lignin structure in Chamaecyparis obtusa, as revealed by double immunolabeling by using monoclonal antibodies

Immunolabeling by using monoclonal antibodies showed that xylan deposition precedes the formation of 8-5'-linked structure of lignin in normal and compression woods of Chamaecyparis obtusa. Xylan deposition and formation of 8-5'-linked lignin structure in differentiating xylems from normal and compression woods in Chamaecyparis obtusa were examined by immunoelectron microscopy using monoclonal antibodies (LM10 or LM11) to detect xylan localization. The 8-5'-linked lignin structure was immunolocalized using KM1 antibody. Xylan and 8-5'-linked lignin double immunolabeling was performed using secondary antibodies labeled with colloidal gold particles of different diameters. In normal wood, KM1 labeling occurred in the compound middle lamella (CML) and S1 layer during S1 layer formation and increased as S2 and S3 layers formed, with labeling occurring at the outer part of the previous layer. In compression wood, mild KM1 labeling occurred in the CML and outer part of the S1 layer at the later S1 layer formation stage, with increased labeling as the S2 layer formed. Minor labeling occurred in the outer part of the S2 layer during helical cavity formation. Comparison between KM1 labeling and KMnO4 staining suggested that lignin other than 8-5'-linked structure was formed during early lignification, and the proportion of 8-5'-linked lignin structure increased at later stages of lignification in both normal and compression woods. LM10 and LM11 labeling occurred slightly earlier than KM1 labeling, suggesting that xylan deposition preceded the formation of 8-5'-linked lignin in normal and compression woods. Less labeling by KM1, LM10, and LM11 occurred in the outer part of the S2 layer in compression wood, which has abundant lignin. Thus, lignin in these parts is composed of lignin substructures other than the 8-5' linkage.

Immunolocalization of hemicelluloses in Arabidopsis thaliana stem. Part I: temporal and spatial distribution of xylans

We investigated the microdistribution of xylans in different cell types of Arabidopsis stem using immunolocalization methods with LM10 and LM11 antibodies. Xylan labeling in xylary fibers (fibers) was initially detected at the cell corner of the S(1) layer and increased gradually during fiber maturation, showing correlation between xylan labeling and general secondary cell wall formation processes in fibers. Metaxylem vessels (vessels) showed earlier development of secondary cell walls than fibers, but revealed almost identical labeling patterns to fibers during maturation. No difference in labeling patterns and intensity was detected in the cell wall of fibers, vessels and protoxylem vessels (proto-vessels) between LM10 and LM11, indicating that vascular bundle cells may be chemically composed of a highly homogeneous xylan type. Interestingly, interfascicular fibers (If-fibers) showed different labeling patterns between the two antibodies and also between different developmental stages. LM10 showed no labeling in primary cell walls and intercellular layers of If-fibers at the S(1) formation stage, but some labeling was detected in middle lamella cell corner regions at the S(2) formation stage. In contrast, LM11 revealed uniform labeling across the If-fiber cell wall during all developmental stages. These results suggest that If-fibers have different xylan deposition processes and patterns from vascular bundle cells. The presence of xylan was also confirmed in parenchyma cells following pectinase treatment. Together our results indicate that there are temporal and spatial differences in xylan labeling between cell types in Arabidopsis stem. Differences in xylan labeling between Arabidopsis stem and poplar are also discussed.

Distribution of glucomannans and xylans in poplar xylem and their changes under tension stress

Present work investigated glucomannan (GM) and xylan distribution in poplar xylem cells of normal- (NW), opposite- (OW) and tension wood (TW) with immunolocalization methods. GM labeling was mostly detected in the middle- and inner S(2) (+S(3)) layer of NW and OW fibers, while xylan labeling was observed in the whole secondary cell wall. GM labeling in vessels of NW and OW was much weaker than in fibers and mostly detected in the S(2) layer, whereas slightly stronger xylan labeling than fibers was detected in the whole secondary cell wall of vessels. Ray cells in NW and OW showed no GM labeling, but strong xylan labeling. These results indicate that GMs and xylans are spatially distributed in poplar xylem cells with different concentrations present in different cell types. Surprisingly, TW showed significant decrease of GM labeling in the normal secondary cell wall of gelatinous (G) fibers compared to NW and OW, while xylan labeling was almost identical indicating that the GM and xylan synthetic pathways in fibers have different reaction mechanisms against tension stress. Unlike fibers, no notable changes in GM labeling were detected in vessels of TW, suggesting that GM synthesis in vessels may not be affected by tension stress. GM and xylan was also detected in the G-layer with slightly stronger and much weaker labeling than the normal secondary cell wall of G-fibers. Differences in GM and xylan distribution are also discussed for the same functional cells found in hardwoods and softwoods.

Localization of cell wall polysaccharides in normal and compression wood of radiata pine: relationships with lignification and microfibril orientation

The distribution of noncellulosic polysaccharides in cell walls of tracheids and xylem parenchyma cells in normal and compression wood of Pinus radiata, was examined to determine the relationships with lignification and cellulose microfibril orientation. Using fluorescence microscopy combined with immunocytochemistry, monoclonal antibodies were used to detect xyloglucan (LM15), β(1,4)-galactan (LM5), heteroxylan (LM10 and LM11), and galactoglucomannan (LM21 and LM22). Lignin and crystalline cellulose were localized on the same sections used for immunocytochemistry by autofluorescence and polarized light microscopy, respectively. Changes in the distribution of noncellulosic polysaccharides between normal and compression wood were associated with changes in lignin distribution. Increased lignification of compression wood secondary walls was associated with novel deposition of β(1,4)-galactan and with reduced amounts of xylan and mannan in the outer S2 (S2L) region of tracheids. Xylan and mannan were detected in all lignified xylem cell types (tracheids, ray tracheids, and thick-walled ray parenchyma) but were not detected in unlignified cell types (thin-walled ray parenchyma and resin canal parenchyma). Mannan was absent from the highly lignified compound middle lamella, but xylan occurred throughout the cell walls of tracheids. Using colocalization measurements, we confirmed that polysaccharides containing galactose, mannose, and xylose have consistent correlations with lignification. Low or unsubstituted xylans were localized in cell wall layers characterized by transverse cellulose microfibril orientation in both normal and compression wood tracheids. Our results support the theory that the assembly of wood cell walls, including lignification and microfibril orientation, may be mediated by changes in the amount and distribution of noncellulosic polysaccharides.

Transgenic soybean plants overexpressing O-acetylserine sulfhydrylase accumulate enhanced levels of cysteine and Bowman-Birk protease inhibitor in seeds

Soybeans provide an excellent source of protein in animal feed. Soybean protein quality can be enhanced by increasing the concentration of sulfur-containing amino acids. Previous attempts to increase the concentration of sulfur-containing amino acids through the expression of heterologous proteins have met with limited success. Here, we report a successful strategy to increase the cysteine content of soybean seed through the overexpression of a key sulfur assimilatory enzyme. We have generated several transgenic soybean plants that overexpress a cytosolic isoform of O-acetylserine sulfhydrylase (OASS). These transgenic soybean plants exhibit a four- to tenfold increase in OASS activity when compared with non-transformed wild-type. The OASS activity in the transgenic soybeans was significantly higher at all the stages of seed development. Unlike the non-transformed soybean plants, there was no marked decrease in the OASS activity even at later stages of seed development. Overexpression of cytosolic OASS resulted in a 58-74% increase in protein-bound cysteine levels compared with non-transformed wild-type soybean seeds. A 22-32% increase in the free cysteine levels was also observed in transgenic soybeans overexpressing OASS. Furthermore, these transgenic soybean plants showed a marked increase in the accumulation of Bowman-Birk protease inhibitor, a cysteine-rich protein. The overall increase in soybean total cysteine content (both free and protein-bound) satisfies the recommended levels required for the optimal growth of monogastric animals.

Occurrence of xylan and mannan polysaccharides and their spatial relationship with other cell wall components in differentiating compression wood tracheids of Cryptomeria japonica

Compression wood (CW) tracheids have different cell wall components than normal wood (NW) tracheids. However, temporal and spatial information on cell wall components in CW tracheids is poorly understood. We investigated the distribution of arabino-4-O-methylglucuronoxylans (AGXs) and O-acetyl-galactoglucomannans (GGMs) in differentiating CW tracheids. AGX labeling began to be detected in the corner of the S(1) layer at the early S(1) formation stage. Subsequently, the cell corner middle lamella (ccML) showed strong AGX labeling when intercellular spaces were not fully formed. AGX labeling was uniformly distributed in the S(1) layer, but showed uneven distribution in the S(2) layer. AGX labeling was mainly detected in the inner S(2) layer after the beginning of the helical cavity formation. The outer S(2) layer showed almost no labeling of low substituted AGXs. Only a very small amount of high substituted AGXs was distributed in the outer S(2) layer. These patterns of AGX labeling in the S(2) layer opposed the lignin and β-1-4-galactan distribution in CW tracheids. GGM labeling patterns were almost identical to AGX labeling in the early stages of CW tracheids, and GGM labeling was detected in the entire S(2) layer from the early S(2) formation stage of CW tracheids with some spatial differences in labeling density depending on developmental stage. Compared with NW tracheids, CW tracheids showed significantly different AGX distributions in the secondary cell wall but similar GGM labeling patterns. No significant differences were observed in labeling after delignification of CW tracheids.

Temporal and spatial diversities of the immunolabeling of mannan and xylan polysaccharides in differentiating earlywood ray cells and pits of Cryptomeria japonica

Wood is composed of various types of cells and each type of cell has different structural and functional properties. However, the temporal and spatial diversities of cell wall components in the cell wall between different cell types are rarely understood. To extend our understanding of distributional diversities of cell wall components among cells, we investigated the immunolabeling of mannans (O-acetyl-galactoglucomannans, GGMs) and xylans (arabino-4-O-methylglucuronoxylans, AGXs) in ray cells and pits. The labeling of GGMs and AGXs was temporally different in ray cells. GGM labeling began to be detected in ray cells at early stages of S(1) formation in tracheids, whereas AGX labeling began to be detected in ray cells at the S(2) formation stage in tracheids. The occurrence of GGM and AGX labeling in ray cells was also temporally different from that of tracheids. AGX labeling began to be detected much later in ray cells than in tracheids. GGM labeling also began to be detected in ray cells either slightly earlier or later than in tracheids. In pits, GGM labeling was detected in bordered and cross-field pit membranes at early stages of pit formation, but not observed in mature pits, indicating that enzymes capable of GGM degradation may be involved in pit membrane formation. In contrast to GGMs, AGXs were not detected in pit membranes during the entire developmental process of bordered and cross-field pits. AGXs showed structural and depositional variations in pit borders depending on the developmental stage of bordered and cross-field pits.