Individual Cell Wall Research Articles

Supercharged cellulases show superior thermal stability and enhanced activity towards pretreated biomass and cellulose

Non-productive binding of cellulolytic enzymes to various plant cell wall components, such as lignin and cellulose, necessitates high enzyme loadings to achieve efficient conversion of pretreated lignocellulosic biomass to fermentable sugars. Protein supercharging was previously employed as one of the strategies to reduce non-productive binding to biomass. However, various questions remain unanswered regarding the hydrolysis kinetics of supercharged enzymes towards pretreated biomass substrates and the role played by enzyme interactions with individual cell wall polymers such as cellulose and xylan. In this study, CBM2a (from Thermobifida fusca) fused with endocellulase Cel5A (from T. fusca) was used as the model wild-type enzyme and CBM2a was supercharged using Rosetta, to obtain eight variants with net charges spanning −14 to +6. These enzymes were recombinantly expressed in E. coli, purified from cell lysates, and their hydrolytic activities were tested against pretreated biomass substrates (AFEX and EA treated corn stover). Although the wild-type enzyme showed greater activity compared to both negatively and positively supercharged enzymes towards pretreated biomass, thermal denaturation assays identified two negatively supercharged constructs that perform better than the wild-type enzyme (∼3 to 4-fold difference in activity) upon thermal deactivation at higher temperatures. To better understand the causal factor of reduced supercharged enzyme activity towards AFEX corn stover, we performed hydrolysis assays on cellulose-I/xylan/pNPC, lignin inhibition assays, and thermal stability assays. Altogether, these assays showed that the negatively supercharged mutants were highly impacted by reduced activity towards xylan whereas the positively supercharged mutants showed dramatically reduced activity towards cellulose and xylan. It was identified that a combination of impaired cellulose binding and lower thermal stability was the cause of reduced hydrolytic activity of positively supercharged enzyme sub-group. Overall, this study demonstrated a systematic approach to investigate the behavior of supercharged enzymes and identified supercharged enzyme constructs that show superior activity at elevated temperatures. Future work will address the impact of parameters such as pH, salt concentration, and assay temperature on the hydrolytic activity and thermal stability of supercharged enzymes.

Microscopic and nanoscale mechanical properties of tonkin cane bamboo measured by advanced AFM methods

Bamboo is a natural composite material with a high strength-to-weight ratio traditionally used in various consumer products as well as in building and modern advanced and sustainable manufacturing technology. While its macroscopic mechanical properties are well known, nanoscale studies of the mechanical properties of the hierarchical structure of bamboo at the level of individual cells and cell walls are lacking. Here we use different AFM-based methods to analyse the mechanical properties of individual bamboo fibres that are the foundation of the hierarchical structure at the nanoscale. The elastic modulus of the fiber in the outer region varies from 7.5 to 8.9 GPa, while that of the inner fiber ranges between 4.1 and 6.1 GPa. The results demonstrate that the fibre stiffness varies in nanoscale regions between fibre interior and the fibre wall and strongly depends on the position of the individual bamboo fibre within the culm. Outer fibres with high cellulose fibril density and low lignin level show low adhesion interaction force (13.5%) in the interface between cellulose and lignin/hemicellulose matrix, hence, resulting in low plastic deformation energy release during mechanical deformation. The implications of the interrelation of plasticity, lignin level, and adhesion force are discussed for the application of bamboo as a high-performance, renewable, and sustainable material.

Thickness measurement of cell walls of closed-cell foams in micro-CT images.

Characterising the microstructure of foams is an important task for improving foam manufacturing processes and building foam numerical models. This study proposed a method for measuring the thickness of individual cell walls of closed-cell foams in micro-CT images. It comprises a distance transform on CT images to obtain thickness information of cell walls, a watershed transform on the distance matrix to locate the midlines of cell walls, identifying the intersections of midlines of cell walls by examining how many regions each pixel on the midlines of cell walls connects with, disconnecting and numbering the midlines of cell walls, extracting the distance values of the pixels on the midlines (or midplanes) of cell walls, and calculating the thickness of individual cell walls by multiplying the extracted distance values by two. Using this method, the thickness of cell walls of a polymeric closed-cell foam was measured. It was found that cell wall thickness measured in 2D images shows larger average values (around 1.5 times) and dispersion compared to that measured in volumetric images.

An investigation on plant cell walls during biomass pyrolysis: A histochemical perspective on engineering applications

The large variation in biomass species, and hence lignocellulosic composition, often results in varying properties and production of pyrolytic products, i.e. bio-char, bio-oil and bio-gas. Hence, understanding of the distribution of individual lignocellulosic components in plant cell walls and its influence on cell structural evolution during pyrolysis is essential to predict biomass behaviour for different engineering applications. Bamboo shoot sections were subjected to histochemical safranin O/fast green solution staining to reveal the distribution of lignocellulosic components in the sample. Stained fresh samples were compared against pyrolysed samples under light and oil immersion microscopy to investigate the structural evolution of primary and secondary cell walls during pyrolysis. Charred samples were subsequently characterised via BET, XRD and Raman spectroscopy to further understand the influence of pyrolytic temperatures on cell transformations. This study provides insights into understanding the devolatilisation and graphitisation characteristics of individual plant cell wall and its lignocellulosic components, thus facilitating biomass selection for targeted applications in energy derivation and/or material engineering without the need of repeating chemical-intensive histochemical and pyrolysis procedures.

Catalytic metal-nucleotide coordinative cytoskeleton on algae cell towards photosynthetic hydrogen production under air.

A metal-nucleotide coordinative cytoskeleton with ascorbate oxidase-like catalytic behavior was constructed on an individual algae cell wall, which endows the engineered cells with the capability of self-generating a localized hypoxic microenvironment around the cell surface, and thus allows the functionality switching from photosynthetic oxygen production to efficient hydrogen evolution for over one month.

The effect of thickness on the transverse shear strength of nomex honeycomb cores

Honeycomb materials are commonly used as cores for sandwich panels. While empirical evidence exists showing that the transverse shear strength of a honeycomb core is affected by its thickness, the accuracy of empirical guidelines and the reasons for the changes in strength are not well understood. Four-point flexural testing of sandwich beams and a detailed cellular finite element model are used to investigate transverse shear failure of Nomex™ honeycomb core material. Transverse shear strengths at varying core thicknesses were compared to manufacturer specifications and used to determine normalised strength correction factors for thickness. These factors correlated well with trends shown in previous literature, where core shear strength decreases with increasing core thickness. The failure mode investigation showed a transition between modes as core thickness increased. The thinner cores experience shear fracturing of individual cell walls followed by local cell wall buckling, intermediate thickness cores initially failed by cell wall local buckling, then fractured and larger thickness cores appeared to fail by overall cell column buckling.

Forgotten Actors: Glycoside Hydrolases During Elongation Growth of Maize Primary Root.

Plant cell enlargement is coupled to dynamic changes in cell wall composition and properties. Such rearrangements are provided, besides the differential synthesis of individual cell wall components, by enzymes that modify polysaccharides in muro. To reveal enzymes that may contribute to these modifications and relate them to stages of elongation growth in grasses, we carried out a transcriptomic study of five zones of the primary maize root. In the initiation of elongation, significant changes occur with xyloglucan: once synthesized in the meristem, it can be linked to other polysaccharides through the action of hetero-specific xyloglucan endotransglycosidases, whose expression boosts at this stage. Later, genes for xyloglucan hydrolases are upregulated. Two different sets of enzymes capable of modifying glucuronoarabinoxylans, mainly bifunctional α-arabinofuranosidases/β-xylosidases and β-xylanases, are expressed in the maize root to treat the xylans of primary and secondary cell walls, respectively. The first set is highly pronounced in the stage of active elongation, while the second is at elongation termination. Genes encoding several glycoside hydrolases that are able to degrade mixed-linkage glucan are downregulated specifically at the active elongation. It indicates the significance of mixed-linkage glucans for the cell elongation process. The possibility that many glycoside hydrolases act as transglycosylases in muro is discussed.

Best Practices for Quasistatic Berkovich Nanoindentation of Wood Cell Walls

For wood and forest products to reach their full potential as structural materials, experimental techniques are needed to measure mechanical properties across all length scales. Nanoindentation is uniquely suited to probe in situ mechanical properties of micrometer-scale features in forest products, such as individual wood cell wall layers and adhesive bondlines. However, wood science researchers most commonly employ traditional nanoindentation methods that were originally developed for testing hard, inorganic materials, such as metals and ceramics. These traditional methods assume that the tested specimen is rigidly supported, homogeneous, and semi-infinite. Large systematic errors may affect the results when these traditional methods are used to test complex polymeric materials, such as wood cell walls. Wood cell walls have a small, finite size, and nanoindentations can be affected by nearby edges. Wood cell walls are also not rigidly supported, and the cellular structure can flex under loading. Additionally, wood cell walls are softer and more prone to surface detection errors than harder inorganic materials. In this paper, nanoindentation methods for performing quasistatic Berkovich nanoindentations, the most commonly applied nanoindentation technique in forest products research, are presented specifically for making more accurate nanoindentation measurements in materials such as wood cell walls. The improved protocols employ multiload nanoindentations and an analysis algorithm to correct and detect errors associated with surface detection errors and structural compliances arising from edges and specimen-scale flexing. The algorithm also diagnoses other potential issues arising from dirty probes, nanoindenter performance or calibration issues, and displacement drift. The efficacy of the methods was demonstrated using nanoindentations in loblolly pine (Pinus taeda) S2 cell wall layers (S2) and compound corner middle lamellae (CCML). The nanoindentations spanned a large range of sizes. The results also provide new guidelines about the minimum size of nanoindentations needed to make reliable nanoindentation measurements in S2 and CCML.

Pathways of microfossil mineralisation by hematite in the 1878 Ma Gunflint Formation

The ~1878 Ma Gunflint Formation contains some of the foremost examples of Palaeoproterozoic life but questions remain regarding the potential metabolic and taphonomic pathways within the microfossil assemblage. Here we report on hematite-mineralised examples of the most abundant Gunflint organisms (Gunflintia and Huroniospora), using correlative light-, Raman- and electron-microscopy to document subtle variations in iron oxide mineralisation styles.Data come from two localities where similar stromatolitic facies are found, namely Schreiber Channel and Mink Mountain, Ontario. At Schreiber Channel, rare hematitic microfossils are found at the margins of small pods of pyritised microorganisms, with some individual cell or sheath walls retaining pyrite cores and hematite rims. Microfossil wall hematite grains form anhedral masses, contain large numbers of quartz inclusions, plus a small number of barium-rich and calcium-rich nano-crystals. Hematitic, pyritic and carbonaceous microfossil preservation styles co-occur within a single petrographic thin section. A sub-set of iron-mineralised fossils at Schreiber have thinner walls, comprising tabular hematite grains plus Fe-Al-silicates and traces of organic material. At Mink Mountain, microfossil walls are ubiquitously preserved as hematite but well-preserved examples occur only in isolated zones of particularly dark brown/purple hematite. Here, hematite grains show a cuspate to anhedral habit with embayment and inclusions of quartz plus rare Ti-rich nano-crystals; nano-particles of iron oxide and rare organic material occur as bridges between some grains.The morphological similarity of microfossil assemblages having walls now preserved with different chemical compositions (carbon, pyrite, Fe-Al-silicate and hematite), and across widely-spaced stromatolitic localities, indicates that iron oxide mineralisation was a taphonomic rather than primary metabolic process. The pyrite and Fe-Al-silicates at Schreiber are interpreted as the earliest stages of iron mineralisation, forming under reducing diagenetic conditions in the presence of excess organic material. Partial replacement of these phases by hematite followed later when oxygen bearing fluids penetrated limited zones within the sediments. At Mink Mountain, we infer that zones of well-preserved microfossils were initially mineralised as pyrite, followed by the complete oxidation of pyrite plus all surrounding organic material to hematite.This study demonstrates the importance of localised micro-environmental conditions on taphonomic processes and, in turn, the role that taphonomy can play in the modification of the morphology of fossilised organisms. This has implications both for the study of early life on Earth and for the assessment of any putative microfossils returned from Mars.

Transcriptomic analysis reveals differences in fruit maturation between two kiwifruit cultivars

The commonly accepted kiwifruit harvest index based solely on soluble solids content (SSC) has lost its original significance owing to the increased sophistication of marketing coupled with the commercialisation of new cultivars, many with yellow flesh when ripe. The precision of novel harvest indices may be improved by a molecular understanding of fruit maturation changes in commonly monitored fruit attributes, including SSC, flesh colour and firmness. Transcriptional changes in the early-maturing Actinidia chinensis var. chinensis ‘Zesy002’ and later maturing A. chinensis var. deliciosa ‘Hayward’, grown at a single site, have been quantified weekly in the period leading up to and past the commercial harvest period. Transcriptomic data highlighted numerous maturation related changes in the fruit, and differences between the two cultivars. Examples of gene changes of relevance for non-structural carbohydrates included the large sub-unit 4 of ADP-glucose pyrophosphorylase (APL4) indicative of starch synthesis, BETA AMYLASE 3.2 (BAM3.2) for starch breakdown and the sugar transporter (SWEET9a). The association between STAYGREEN2 (SGR2) with flesh degreening was strong in ‘Zesy002’, although a later increase in ‘Hayward’ to levels similar to those in ‘Zesy002’ was not accompanied by an equivalent flesh colour change. In ‘Zesy002’ there were numerous individual cell wall gene changes associated with the change to rapid softening, including EXPANSIN7 (EXP7), POLYGALACTURONASE1 (PG1), PECTATE LYASE (PL), PECTIN METHYL ESTERASE (PME) and XYLOGLUCAN TRANSGLYCOSYLASE/ HYDROLASE (XTH). However, among these genes, it is possible to see similar changes in ‘Hayward’ which were not associated with a marked change in softening rate, including for EXP7 and PG1. The most obvious start points for changes in transcription of these genes were the seed coat colour change, the cessation of growth, and the change to ripening (rapid softening and starch breakdown). The findings are discussed with respect to fruit maturation and the possible use of gene markers as harvest indices.

Design and modeling of bamboo biomorphic structure for in-plane energy absorption improvement

Bamboo cell wall exhibits a microscopically graded architecture, and micro-layer distributed cells around individual cell walls, which leads to the preferred mechanical properties of bamboo for impact loading. This work proposes a cellular structure, as called Bamboo Biomorphic Structure (BBS), which is a functionally graded honeycomb cellular structure inspired by the microstructure of bamboo and manufactured using fused filament fabrication (FFF). It is hypothesized that, by introducing bamboo biomorphic micro-unit cells, including a range of thickness step differences within an individual honeycomb unit cell, the successive stages of deformation of the honeycomb structure can be controlled, making the system absorb impact energy more efficiently. Characterization of the designed structures was conducted under in-plane quasi-static loading conditions, and then evaluated using a nonlinear finite element commercial code LS-DYNA. The proposed gradient BBS showed higher absorbed impact energies by four times compared with the conventional Honeycomb structure.The proposed parametric design would aid engineering design principles for the development of a novel biomorphic cellular structure, which has the potential for large-scale manufacturing of efficient energy-absorbing engineering structures. Such an energy-absorbing structure can help improve the lightweight structure design for various applications, including automobiles and aircrafts, while ensuring safety under impact load.

Topochemical and light microscopic investigations of non-enzymatic oxidative changes at the initial decay stage of furfuryl alcohol-modified radiata pine (Pinus radiata) degraded by the brown rot fungus Rhodonia placenta

The aim of this study was to visualize non-enzymatic oxidative degradation damages in the initial decay stage of the brown rot fungus Rhodonia placenta degradation in furfuryl alcohol (FA) modified wood cell walls and untreated wood cell walls of radiata pine (Pinus radiata) sapwood. A decay test with small wood blocks (1.5 × 1.5 × 5 mm³) of untreated and furfurylated radiata pine selected from two different furfurylation processes was performed until the first mass loss occurred. The samples were exposed to the brown rot fungus R. placenta, monitored by light microscopy and analyzed topochemically by cellular UV microspectrophotometry (UMSP). The results showed that the FA modification process directly influenced: i) the fungal colonization and hyphal growth, ii) the spectral UV behavior, and iii) degradation patterns of the entire cell wall layers. For the first time, UMSP area scans and selective line scans of individual cell wall regions provide topochemical insights into oxidative degradation at the initial decay stage of furfuryl alcohol-modified P. radiata visualizing oxidative degradation in situ. Knowledge of the initial decay stage of brown rot degradation in FA-modified wood compared to untreated wood extends our understanding of the brown rot decay processes of cell wall compounds.

EgPHI-1, a PHOSPHATE-INDUCED-1 gene from Eucalyptus globulus, is involved in shoot growth, xylem fiber length and secondary cell wall properties.

EgPHI-1 is a member of PHI-1/EXO/EXL protein family. Its overexpression in tobacco resulted in changes in biomass partitioning, xylem fiber length, secondary cell wall thickening and composition, and lignification. Here, we report the functional characterization of a PHOSPHATE-INDUCED PROTEIN 1 homologue showing differential expression in xylem cells from Eucalyptus species of contrasting phenotypes for wood quality and growth traits. Our results indicated that this gene is a member of the PHI-1/EXO/EXL family. Analysis of the promoter cis-acting regulatory elements and expression responses to different treatments revealed that the Eucalyptus globulus PHI-1 (EgPHI-1) is transcriptionally regulated by auxin, cytokinin, wounding and drought. EgPHI-1 overexpression in transgenic tobacco changed the partitioning of biomass, favoring its allocation to shoots in detriment of roots. The stem of the transgenic plants showed longer xylem fibers and reduced cellulose content, while the leaf xylem had enhanced secondary cell wall thickness. UV microspectrophotometry of individual cell wall layers of fibers and vessels has shown that the transgenic plants exhibit differences in the lignification of S2 layer in both cell types. Taken together, the results suggest that EgPHI-1 mediates the elongation of secondary xylem fibers, secondary cell wall thickening and composition, and lignification, making it an attractive target for biotechnological applications in forestry and biofuel crops.

The chromatin-modifying protein HUB2 is involved in the regulation of lignin composition in xylem vessels.

PIRIN2 (PRN2) was earlier reported to suppress syringyl (S)-type lignin accumulation of xylem vessels of Arabidopsis thaliana. In the present study, we report yeast two-hybrid results supporting the interaction of PRN2 with HISTONE MONOUBIQUITINATION2 (HUB2) in Arabidopsis. HUB2 has been previously implicated in several plant developmental processes, but not in lignification. Interaction between PRN2 and HUB2 was verified by β-galactosidase enzymatic and co-immunoprecipitation assays. HUB2 promoted the deposition of S-type lignin in the secondary cell walls of both stem and hypocotyl tissues, as analysed by pyrolysis-GC/MS. Chemical fingerprinting of individual xylem vessel cell walls by Raman and Fourier transform infrared microspectroscopy supported the function of HUB2 in lignin deposition. These results, together with a genetic analysis of the hub2 prn2 double mutant, support the antagonistic function of PRN2 and HUB2 in deposition of S-type lignin. Transcriptome analyses indicated the opposite regulation of the S-type lignin biosynthetic gene FERULATE-5-HYDROXYLASE1 by PRN2 and HUB2 as the underlying mechanism. PRN2 and HUB2 promoter activities co-localized in cells neighbouring the xylem vessel elements, suggesting that the S-type lignin-promoting function of HUB2 is antagonized by PRN2 for the benefit of the guaiacyl (G)-type lignin enrichment of the neighbouring xylem vessel elements.

Atomic force microscopy imaging of delignified secondary cell walls in liquid conditions facilitates interpretation of wood ultrastructure

Deep understanding of the physicochemical and structural characteristics of wood at the nanoscale is essential for improving wood usage in biorefining and advancing new high performance materials design. Herein, we use in situ atomic force microscopy and a simple delignification treatment to elucidate the nanoscale architecture of individual secondary cell wall layers. Advantages of this approach are: (i) minimal sample preparation that reduces the introduction of potential artifacts; (ii) prevention of structural rearrangements due to dehydration; (iii) increased accessibility to structural details masked by the lignin matrix; and (iv) possibility to complement results with other analytical techniques without sample manipulation. The methodology permits the visualization of parallel and helicoidally arranged microfibril aggregates in the S1 layer and the determination of lignin contribution to microfibril aggregates forming S2 layers. Cellulose and hemicelluloses constitute the core of the aggregates with a mean diameter of approximately 19 nm, and lignin encloses the core forming single structural entities of about 30 nm diameter. Furthermore, we highlight the implications of sample preparation and imaging parameters on the characterization of microfibril aggregates by AFM.

Crude Xylanases and Pectinases from Bacillus spp. Along with Commercial Cellulase Formulate an Efficient Tailor-Made Cocktail for Sugarcane Bagasse Saccharification

Restricted activities of individual plant cell wall–degrading enzymes, i.e., cellulase, xylanase, and pectinase, on plant biomass are due to the complex interactions among structural polysaccharides and lignin components of plant cell wall. This can be overcome through altering the structural components by subjecting biomass to physicochemical pretreatments. In present studies, experiments were undertaken with the rationale that applying tailor-made cocktail formulations to pretreated biomass, by striking a synergy between core cellulolytic (C) and/or accessory xylano-pectinolytic (X, P) enzymes from the Bacillus strains B. safensis M35, B. altitudinis R31 and B. altitudinis J208, should enhance the saccharification. Efficiency of individual and substitutive cocktails for saccharification of raw, NaOH, and NH4OH pretreated sugarcane bagasse was demonstrated and compared. Among the individual CP, CX, PX, and CPX cocktails, the CPX cocktails yielded enhanced and maximum saccharification of 71.4–81.3% and 17.0–17.28% from NaOH and NH4OH pretreated biomass as compared to the 7.1–7.6% from raw. After finding xylanases and pectinases from the three Bacillus strains compatible with each other, substitutive cocktail CPXsub was prepared by putting all these accessory enzymes with core cellulase. This enhanced saccharification to 84.02% and 25.52% from NaOH and NH4OH pretreated biomass as compared to 8.91% from raw. With the support of HPLC, FTIR, and SEM analyses, results clearly confirmed the high saccharifying potential of tailor-made substitutive cocktails due to synergistic and accessory nature of xylanases and pectinases to the core commercial cellulase.

Micromechanical Characterization of Metal Foams

Cellular materials such as foams, honeycombs, or auxetic structures are an interesting type of structural materials for lightweight constructions or dynamic energy absorbers. These microheterogeneous materials consist of a hierarchical structure. Foams can be separated into a macro scale, meso scale, and micro scale dealing with the entire specimen or component, individual pores, and individual struts, respectively. As a result, the macroscopic foam properties are strongly related to the mesoscopic and microscopic properties as a superposition of geometrical structural response and material properties. Whereas the geometry can be easily determined, e.g., by computer tomography measurements, the evaluation of real micro material properties of individual struts or cell walls is still a very challenging task. The material properties of these constituents of open‐cell or closed‐cell foams significantly differ from bulk material properties due to changes in boundary condition during production and different scaling effects, such as different surface‐to‐volume ratios of oxide layers or different cooling conditions due to less material in struts than in the bulk. However, the need for reliable micro material properties for the realistic forecast of macroscopic properties of components made of foam by numerical simulations makes the micromechanical characterization and testing of metal foams to an emerging field of research. The present contribution deals with the most relevant achievements in the field from the beginnings to the present day.

Evaluation of fungal degradation of wheat straw cell wall using different analytical methods from ruminant nutrition perspective.

BACKGROUNDWhite rot fungi have been used to improve the nutritive value of lignocellulose for ruminants. In feed analysis, the Van Soest method is widely used to determine the cell wall contents. To assess the reliability of this method (Method A) for determination of cell wall contents in fungal‐treated wheat straw, we compared a combined monosaccharide analysis and pyrolysis coupled to gas chromatography with mass spectrometry (Py‐GC/MS) (Method B). Ruminal digestibility, measured as in vitro gas production (IVGP), was subsequently used to examine which method explains best the effect of fungal pretreatment on the digestibility of wheat straw.RESULTSBoth methods differed considerably in the mass recoveries of the individual cell wall components, which changed on how we assess their degradation characteristics. For example, Method B gave a higher degradation of lignin (61.9%), as compared to Method A (33.2%). Method A, however, showed a better correlation of IVGP with the ratio of lignin to total structural carbohydrates, as compared to Method B (Pearson's r of −0.84 versus −0.69). Nevertheless, Method B provides a more accurate quantification of lignin, reflecting its actual modification and degradation. With the information on the lignin structural features, Method B presents a substantial advantage in understanding the underlying mechanisms of lignin breakdown. Both methods, however, could not accurately quantify the cellulose contents – among others, due to interference of fungal biomass.CONCLUSIONMethod A only accounts for the recalcitrant residue and therefore is more suitable for evaluating ruminal digestibility. Method B allows a more accurate quantification of cell wall, required to understand and better explains the actual modification of the cell wall. The suitability of both methods, therefore, depends on their intended purposes. © 2019 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Cell Wall Compositional Analysis of Rice Culms.

The plant cell wall is a complicated network that is mainly constituted of polysaccharides, such as cellulose, hemicellulose and pectin. Many noncellulosic polysaccharides are further acetylated, which confers these polymers flexible physicochemical properties. Due to the significance of cell wall in plant growth and development, the analytic platform has been the focus for a long time. Here, we use internodes/culms, an important organ to provide mechanical support for rice plants, as an experimental sample to explore the method for cell wall composition analysis. The method includes preparation of cell wall residues, sequential extraction of polysaccharides, and measurement of cellulose. The procedure for acetate examination is also described. This method is applicable to determine the composition of individual cell wall polymers and the modifier acetates, and is suitable to identify cell wall relevant mutants based on the advantages in high throughput, precision and repeatability.

X-ray methods to observe and quantify adhesive penetration into wood

To accelerate development of new and improved wood adhesives for engineered wood products, the optimal adhesive penetration into wood needs to be better understood for specific products and applications. Adhesive penetration includes both flow of adhesives into wood micron-scale voids and infiltration into the polymer components of the wood cell wall layers. In this work, X-ray computed tomography (XCT) and X-ray fluorescence microscopy (XFM) were used to study adhesive flow and infiltration. Model wood–adhesive bondlines were made using loblolly pine (Pinus taeda) latewood substrates and bromine-substituted phenol formaldehyde (BrPF) resins with different weight-average molecular weights (MW). The Br substitution facilitated both qualitative and quantitative observations using XCT and XFM. The BrPF resin flow into wood was visualized using XCT volume reconstructions and quantified by calculating the weighted penetration (WP). Examination of the shape of the cured BrPF–air interface in longitudinal tracheid lumina revealed that capillary action often played a role in BrPF flow. XFM mapping revealed the pathways of BrPF infiltration into the wood cell walls, and the results were used to calculate BrPF cell wall weight percent gain (WPGCW) in individual wood cell walls. Both WP and WPGCW decreased with increasing BrPF MW. Additionally, the middle lamella had higher WPGCW than its neighboring secondary cell walls, and within a given bondline the WPGCW decreased with increasing distance of the cell from the bondline. The results provide new insights that are needed in the development of improved models to understand and predict wood–adhesive bondline performance.