Compound Middle Lamella Research Articles

Unveiling the Dissolution Regularities of the Lignin-Carbohydrate Complex in Bamboo Cell Walls during Alkali Pretreatment.

Bamboo is a promising biomass resource. However, the complex multilayered structure and chemical composition of bamboo cell walls create a unique anti-depolymerization barrier, which increases the difficulty of separation and utilization of bamboo. In this study, the relationship between the connections of lignin-carbohydrate complexes (LCCs) within bamboo cell walls and their multilayered structural compositions was investigated. The chemical composition, structural properties, dissolution processes, and migration mechanisms of LCCs were analyzed. Alkali-stabilized LCC bonds were found to be predominantly characterized by phenyl glycoside (PhGlc) bonds along with numerous p-coumaric acid (PCA) linkage structures. As demonstrated by the NMR and CLSM results, the dissolution of the LCC during the alkaline pretreatment process was observed to migrate from the inner secondary wall (S-layer) of the bamboo fiber cell walls to the cell corner middle lamella (CCML) and compound middle lamella (CML), ultimately leading to its release from the bamboo. Furthermore, the presence of H-type lignin-FA-arabinoxylan linkage structures within the bamboo LCC was identified with their primary dissolution observed in the S-layer of the bamboo fiber cell walls. The study results provided a clear target for breaking down the anti-depolymerization barrier in bamboo, signifying a major advancement in achieving the comprehensive separation of bamboo components.

Revealing the structure and distribution changes of corn stalk lignin during the Organosolv Pretreatment

During the pretreatment of biomass, the research on the migration process of lignin in the cell wall and the change of chemical structure is very important for improving pretreatment and subsequent lignin upgrading. Hence, corn stalk lignin was extracted by 1, 4-dioxane organosolv system under mild conditions with varying pretreatment time and 0.1 M hydrochloric acid as catalyst. The heterogeneity of lignin removal in the different morphological areas of the cell wall was revealed by advanced imaging techniques. Results indicated that during the pretreatment with dioxane organosolv, the removal of lignin started from the secondary wall of the cell wall, and gradually developed outward to the compound middle lamella. Meanwhile, the resulting lignin obtained through different pretreatment times was characterized by two-dimensional heteronuclear single quantum coherence spectroscopy (2D-HSQC) and gel permeation chromatography (GPC). These characterization results indicated that there were more syringyl (S) units in the lignin that were removed first, and the proportion of guaiacyl (G) units was increased as the pretreatment continued. All the evidence supports the idea that the main reason for the significant differences in lignin structures at various periods of the lignin removal process is that the lignin come from different cell wall regions.

Effects on stone cell development and lignin deposition in pears by different pollinators.

The pear pulp is formed by the development of the ovary wall, which is the somatic cell of the female parent, and its genetic traits are identical to those of the female parent, so that its phenotypic traits should also be identical to those of the female parent. However, the pulp quality of most pears, especially the stone cell clusters (SCCs) number and degree of polymerization (DP), were significantly affected by the paternal type. Stone cells are formed by the deposition of lignin in parenchymal cell (PC) walls. Studies on the effect of pollination on lignin deposition and stone cell formation in pear fruit have not been reported. Methods: In this study, 'Dangshan Su' (P. bretschneideri Rehd.) was selected as the mother tree, while 'Yali' (P. bretschneideri Rehd.) and 'Wonhwang' (P. pyrifolia Nakai.) were used as the father trees to perform cross-pollination. We investigated the effects of different parents on SCCs number and DP, and lignin deposition by microscopic and ultramicroscopic observation. The results showed that the formation of SCCs proceeds was consistent in DY and DW, but the SCC number and DP in DY were higher than that in DW. Ultramicroscopy revealed that the lignification process of DY and DW were all from corner to rest regions of the compound middle lamella and the secondary wall, with lignin particles deposited along the cellulose microfibrils. They were alternatively arranged until they filled up the whole cell cavity to culminate in the formation of stone cells. However, the compactness of the wall layer of cell wall was significantly higher in DY than in DW. We also found that the pit of stone cell was predominantly single pit pair, they transported degraded material from the PCs that were beginning to lignify out of the cells. Stone cell formation and lignin deposition in pollinated pear fruit from different parents were consistent, but the DP of SCCs and the compactness of the wall layer were higher in DY than that in DW. Therefore, DY SCC had a higher ability to resist the expansion pressure of PC.

Disrupted cellulose aggregation leads to the reduced mechanical performance of wood–adhesive interphase during freeze–thaw cycles

The mechanical performance of engineered wooden products facing the freeze–thaw cycles (FTCs) arises as an attention-worthy issue since the application of timber architectures in cold climates spreads. Here, we reported an investigation to reveal the losses of the mechanical performance of the wood-phenol formaldehyde (PF) adhesive interphase after the FTCs. Results revealed that PF adhesive was barely affected by the FTCs due to the low moisture content and rigid networks, whereas the mechanical properties of the cell wall in wood-PF interphase reduced significantly (more than 30%) after 5 FTCs at – 40 °C. Cracks were observed in the cell wall and compound middle lamella after FTCs. Further investigation into the crystal structure of the cell wall in the wood-PF interphase demonstrated that the FTCs disrupt the aggregations of cellulose macromolecules. The stresses caused by the phase transition of free water and the external hydrogen bonds formed between water and cellulose disrupted hydrogen bond networks in the cell wall. A plausible mechanism for the FTCs reducing the mechanical properties of the wood-PF bonds can be concluded as the cracks and weakened cell walls crippled the structural integrity of the wood-PF interphase, making it a fragile and stress-concentrated site when subjected to load.

Ginkgo seed shell provides a unique model for bioinspired design

Natural structural materials typically feature complex hierarchical anisotropic architectures, resulting in excellent damage tolerance. Such highly anisotropic structures, however, also provide an easy path for crack propagation, often leading to catastrophic fracture as evidenced, for example, by wood splitting. Here, we describe the weakly anisotropic structure of Ginkgo biloba (ginkgo) seed shell, which has excellent crack resistance in different directions. Ginkgo seed shell is composed of tightly packed polygonal sclereids with cell walls in which the cellulose microfibrils are oriented in a helicoidal pattern. We found that the sclereids contain distinct pits, special fine tubes like a "screw fastener," that interlock the helicoidal cell walls together. As a result, ginkgo seed shell demonstrates crack resistance in all directions, exhibiting specific fracture toughness that can rival other highly anisotropic natural materials, such as wood, bone, insect cuticle, and nacre. In situ characterization reveals ginkgo's unique toughening mechanism: pit-guided crack propagation. This mechanism forces the crack to depart from the weak compound middle lamella and enter into the sclereid, where the helicoidal cell wall significantly inhibits crack growth by the cleavage and breakage of the fibril-based cell walls. Ginkgo's toughening mechanism could provide guidelines for a new bioinspired strategy for the design of high-performance bulk materials.

An in-situ microscale investigation into the fracture of wood-adhesive interphase by nanoindentation

• Micropillar compression accompanied by FEA simulation was applied to investigate the fracture of wood-adhesive interphase. • Yield strength of microscale wood-adhesive interphase was contingent with the interpenetrating polymer networks (IPNs). • A crack-dominated fracture mode was found when compressing the wood-adhesive interphase comprising cell wall and adhesive. Green timber high-rises now taking off raises the desire to improve the mechanical performance and durability of engineered wood-based composites. It requires an in-depth understanding of the fracture mechanism of wood-adhesive interphase. Nanoindentation (NI) analyses in conjunction with finite element analysis (FEA) were conducted in this work to reveal the fracture behaviors and static mechanical properties of microscale wood-adhesive interphases composed of different cell wall layers and phenol–formaldehyde (PF) adhesive. Results revealed the evident cracks and bending in microscale wood-adhesive interphase, which originates from the stress concentration at the interfacial interlock of the cell walls and PF adhesive. Deformation of compound middle lamella (CML) located far from the bond line was prior to other microscale wood-adhesive interphases. Prolongation of cracks contributes to the fracture of wood substrates, and brittle fracture of adhesive leads to the deconstruction of wood-adhesive interphase. Results also demonstrated that compact interpenetrating polymer networks (IPNs) impart the corresponding wood-adhesive interphase with the favored yield strength (281 MPa) because of the improved stress transferring. Therefore, building compact IPNs is beneficial for fabricating a strengthened and toughened wood-adhesive interphase in engineered wood-based composites.

The differences of viscoelastic properties between the secondary wall S2 layer and compound middle lamella of thermally treated wood

The differences of viscoelastic properties between the secondary wall S2 layer and compound middle lamella of thermally treated wood

Deposition patterns of feruloylarabinoxylan during cell wall formation in moso bamboo.

The feruloylarabinoxylan deposition was initiated at the formation of the secondary cell wall, especially S2 layer in moso bamboo, which may affect crosslinking between cell wall components and plant growth. Hemicelluloses, major components of plant cell walls that are hydrogen bonded to cellulose and covalently bound to lignin, are crucial determinants of cell wall properties. Especially in commelinid monocotyledons, arabinoxylan is often esterified with ferulic acid, which is essential to crosslinking with cell wall components. However, the deposition patterns and localization of ferulic acid during cell wall formation remain unclear. In this study, developing moso bamboo (Phyllostachys pubescens) culms were used to elucidate deposition patterns of hemicelluloses including feruloylarabinoxylan. Ferulic acid content peaked with cessation of elongation growth, and thereafter decreased and remained stable as culm development proceeded. During primary cell wall (PCW) formation, xyloglucan and (1,3;1,4)-β-glucan signals were detected in all tissues. Along with culm development, arabinoxylan and feruloylarabinoxylan signals were sequentially observed in the protoxylem, vascular fibers and metaxylem, and parenchyma. Feruloylarabinoxylan signals were observed slightly later than arabinoxylan signals. Arabinoxylan signals were observed throughout the compound middle lamella and secondary cell wall (SCW), whereas the feruloylarabinoxylan signal was localized to the S2 layer of the SCW. These results indicate that the biosynthesis of hemicelluloses is regulated in accordance with cell wall layers. Feruloylarabinoxylan deposition may be initiated at the formation of SCW, especially S2 layer formation. Ferulic acid-mediated linkages of arabinoxylan-arabinoxylan and arabinoxylan-lignin would arise during SCW formation with the cessation of elongation growth.

Effect of Impregnation with a Low-Concentration Furfuryl Alcohol Aqueous Solution on Hygroscopic Properties of Chinese Fir and Poplar Wood

Furfurylation with a low concentration of furfuryl alcohol (FA) promotes the improvement of the properties and the effectiveness of FA on cell–wall action without darkening the furfurylated wood to the point that it affects its applications. In this paper, the effects of furfurylation on the hygroscopicity and water uptake dimensional stability of poplar (Populus sp.) and Chinese fir (Cunninghamia lanceolata) were analyzed. Meanwhile, the distribution of FA resin, the relationship between wood and water, the change in pore size distribution, and the weight percentage gain and cell wall bulking coefficient of wood were also investigated. The results were as follows: (1) A low concentration of FA could better enter the cell walls of the Chinese fir than the poplar, as FA resin was almost cured in the secondary walls, cell corners, and compound middle lamellae when a 10% concentration of FA was applied to the Chinese fir and poplar. When the FA concentration was increased to 30%, there were no significant increases in the amount of FA entering the cell walls and the amounts of FA cured in the cell lumen of the poplar were greater than those of the Chinese fir. Meanwhile, the modification of cell walls was more suitable in poplar than in Chinese fir. (2) The pointed ends of the pit chambers and the pit apertures (800–1000 nm) in the poplar and the small pores of the pit membranes and the pit apertures (1–6 μm) in the Chinese fir were partially deposited by the FA resin, which formed new pores in the size ranges of 80–600 nm and 15–100 nm, respectively. The porosity of the poplar was greater than that of the Chinese fir, and the bulk density of the poplar was less than that of the Chinese fir before and after modification. (3) Furfurylation with a low concentration of FA was able to better reduce the equilibrium moisture content, improve the anti-swelling efficiency, and enhance the dimensional stability of the poplar wood compared to the Chinese fir. Furfurylation effectively reduced water uptake due to the hydrophobic property of the FA resin. The water uptake of the Chinese fir increased by 17%–19% in second cyclic water soaking when treated with FA with various concentrations, which indicated the loss and leaching of FA resin during the test. Low-field NMR was used to demonstrate that the furfurylation not only reduced the amount of water but also affected the combination state of bound and free water with wood. Thus, furfurylation at a low concentration is a feasible method by which to extend applications of furfurylated wood.

Intercellular Matrix Infiltration Improves the Wet Strength of Delignified Wood Composites.

Delignified wood (DW) represents a promising bio-based fibrous material as a reinforcing component in high-performance composites. These cellulose composites possess excellent strength and stiffness in the dry state, which are significantly higher than for natural wood. However, in the wet state, a penetrating water layer enters the intercellular regions and disrupts the stress transfer mechanisms between cell fibers in fully DW. This water layer initially facilitates complex shaping of the material but imparts DW composites with very low wet stiffness and strength. Therefore, a sufficient stress transfer in the wet state necessitates a resin impregnation of these intercellular regions, establishing bonding mechanisms between adjacent fibers. Here, we utilize a water-based dimethyloldihydroxyethylene urea thermosetting matrix (DMDHEU) and compare it with a non-water-based epoxy matrix. We infiltrate these resins into DW and investigate their spatial distribution by scanning electron microscopy, atomic force microscopy, and confocal Raman spectroscopy. The water-based resin impregnates the intercellular areas and generates an artificial compound middle lamella, while the epoxy infiltrates only the cell lumina of the dry DW. Tensile tests in the dry and wet states show that the DMDHEU matrix infiltration of the intercellular areas and the cell wall results in a higher tensile strength and stiffness compared to the epoxy resin. Here, the artificial compound middle lamella made of DMDHEU bonds adjacent fibers together and substantially increases the composites' wet strength. This study elucidates the importance of the interaction and spatial distribution of the resin system within the DW structure to improve mechanical properties, particularly in the wet state.

Enhancing the mechanical properties and hydrophobicity of heat-treated wood by migrating and relocating sulfonated lignin

Abstract Heat-treated wood (HTW) has better dimensional stability but worse mechanical strength than untreated wood. This study aimed to overcome this shortcoming by sulfonating lignin in Balfour spruce (Picea likiangensis var. balfouriana) wood with sulfurous acid and Na2SO3 followed by heat treatment. The mass loss of as-prepared HTW decreased while the crystallinity index increased slightly compared with those of HTW without sulfonation pretreatment. The cellulose structure of the as-prepared HTW was not damaged by the sulfonation pretreatment. The as-prepared HTW showed a higher MOE, MOR, and compressive strength (CS) of 34, 32, and 22%, respectively, compared with the HTW without sulfonation treatment. The improved mechanical properties were attributed to the increase of the relative mass fraction of lignin in the secondary walls of wood, as sulfonated lignin could migrate with water from the compound middle lamellae into the secondary wall under the combined driving forces of a concentration difference and steam pressure. These findings provide a way to enhance the mechanical properties of HTW while gaining better hydrophobicity.

A Structural Assessment of Sycamore Maple Bark Disintegration by Nectria cinnabarina

Previous phytopathological studies of the fungal pathogen Nectria cinnabarina have been focused on its distribution and host diversity but little is known about the spread of this pathogen and the defence responses of forest trees to an infection inside host tissues. Histopathological alterations of bark, periderm, phloem and woody tissues were investigated in sycamore maple (Acer pseudoplatanus) branches following their natural attack by the advanced anamorph and teleomorph developmental stages of the fungus. Light, fluorescence, confocal laser scanning and scanning electron microscopy techniques supplemented by X-ray micro-computed tomography imaging were used to distinguish between healthy and disintegrated plant tissues. The intercellular spread of fungal hyphae was found primarily in the phelloderm. Expanding hyphae aggregations produced ruptures in the phellem and the disintegration of both phellogen and phellodermal parenchyma cells in close proximity to the expanding fruiting bodies of the fungus. Thicker hyphae of the teleomorph fungal stage heavily disintegrated the phelloderm tissues and also induced enhanced sclerification of the nearby phloem tissues that limited the spread of the infection into the sieve tubes. Both the intercellular and intracellular spread of hyphae inside the peripheral parts of sclereid clusters led to the disintegration of the compound middle lamellae but the hyphae were only rarely able to pass through these structural phloem barriers. The massive fungal colonization of both lumens and disintegrated tangential cell walls of ray parenchyma cells resulted in severe cambial necroses. Although the hyphae penetrated into the outermost annual growth rings of the xylem, no cell wall disintegration of the parenchyma cells, vessels and fibres was revealed. Despite the local cambial necroses and severe phloem ray disintegration, the bark remained attached to the examined branches and no bark cankers were formed.

Assessing the availability of two bamboo species for fermentable sugars by alkaline hydrogen peroxide pretreatment

This study comprehensively investigated two bamboo species (i.e. Neosinocalamus affinis and Phyllostachys edulis) in terms of their cell wall ultrastructure, chemical compositions, enzymatic saccharification, and lignin structure before and after alkaline hydrogen peroxide pretreatment (AHP). During AHP, Neosinocalamus affinis (NAB) had higher delignification than Phyllostachys edulis (PEB), and thus showed better enzymatic digestibility (93.05% vs 53.57% for glucan). The fundamental chemical behavior of the bamboo lignins was analyzed by fluorescence microscope (FM), confocal Raman microscope (CRM), molecular weight analysis, and 2D HSQC-NMR. Results indicated that the PEB has thicker cell wall and more concentrated lignin in its compound middle lamella and cell corner middle lamella than NAB. Moreover, PEB lignin contains more G units (S/G of 0.95), in evident contrast to that of NAB lignin (S/G of 1.30), which favor the formation of C–C linkages, thus impeding its degradation during the AHP.

Evaluation of pretreatment effect on lignin extraction from wheat straw by deep eutectic solvent

To investigate the effect of hemicellulose removal on subsequent choline chloride and lactic acid (ChCl-LA) based deep eutectic solvent (DES) extraction of wheat straw lignin, ChCL-LA of DES and hot water presoaking pretreatments were used for hemicellulose prehydrolysis. Both presoakings led to a significant hemicellulose removal and introduced morphological changes on fiber cell wall surface. DES presoaking also instigated ether bonds cleavage between lignin and hemicellulose and selectively removed lignin in compound middle lamella (CML) and cell corner (CC) leading to cell wall disruption and swelling which facilitated lignin extraction. Hot water presoaking removed more hemicellulose and caused a migration of lignin to fibers surface, but did not improve subsequent lignin extraction. This study demonstrated that a two-stage DES treatment method, presoaking at room temperature followed by extracting at an elevated temperature, is a viable process to produce high yield and purity of lignin.

REPRISAL: mapping lignification dynamics using chemistry, data segmentation, and ratiometric analysis.

This article describes a methodology for detailed mapping of the lignification capacity of plant cell walls that we have called "REPRISAL" for REPorter Ratiometrics Integrating Segmentation for Analyzing Lignification. REPRISAL consists of the combination of three separate approaches. In the first approach, H*, G*, and S* monolignol chemical reporters, corresponding to p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol, are used to label the growing lignin polymer in a fluorescent triple labeling strategy based on the sequential use of three main bioorthogonal chemical reactions. In the second step, an automatic parametric and/or artificial intelligence segmentation algorithm is developed that assigns fluorescent image pixels to three distinct cell wall zones corresponding to cell corners, compound middle lamella and secondary cell walls. The last step corresponds to the exploitation of a ratiometric approach enabling statistical analyses of differences in monolignol reporter distribution (ratiometric method [RM] 1) and proportions (RM 2) within the different cell wall zones. We first describe the use of this methodology to map developmentally related changes in the lignification capacity of wild-type Arabidopsis (Arabidopsis thaliana) interfascicular fiber cells. We then apply REPRISAL to analyze the Arabidopsis peroxidase (PRX) mutant prx64 and provide further evidence for the implication of the AtPRX64 protein in floral stem lignification. In addition, we also demonstrate the general applicability of REPRISAL by using it to map lignification capacity in poplar (Populus tremula × Populus alba), flax (Linum usitatissimum), and maize (Zea mays). Finally, we show that the methodology can be used to map the incorporation of a fucose reporter into noncellulosic cell wall polymers.

Cell wall polymer distribution in bamboo visualized with in situ imaging FTIR

To better understand the high recalcitrance of bamboo during bioconversion, the fine spatial distribution of polymers in bamboo was studied with Imaging FTIR microscopy under both transmission and ATR modes, combined with PCA data processing. The results demonstrated that lignin, xylan and hydroxycinnamic acid (HCA) were more concentrated in the fibers near the xylem conduit, while cellulose was evenly distributed across the whole fiber sheath. PCA processing produced a clear separation between bamboo fibers and parenchyma cells, indicating that the parenchyma cells contains more pectin and HCA than fibers. It also demonstrated that cellulose, xylan and S-lignin were concentrated most heavily in bamboo fiber secondary cell walls, while G-lignin, pectin and HCA were found more in the compound middle lamella. The revealed information regarding polymer distribution is of great significance for better understanding of the inherent design mechanism of plant cell wall and its efficient utilization.

Histochemical structure and tensile properties of birch cork cell walls

Tensile tests of birch cork were performed in the tangential direction. Birch cork in the wet state showed significantly higher extensibility than those in the dried state. The histochemical structure of birch cork was investigated by microscopic observation and spectroscopic analysis. Birch cork cell walls showed a two-layered structure and the inner material bordering cell wall. In transmission electron micrographs, osmium tetroxide stained the outer layer and inner material, whereas potassium permanganate stained the inner layer and inner material. After removal of suberin and lignin, only inner layer remained and Fourier-transformed infrared spectra showed the cellulose I pattern. Polarizing light micrographs indicated that molecular chains in the outer layer and inner material were oriented perpendicular to suberin lamination, whereas those in the inner layer showed longitudinal orientation. These results suggested that the outer layer and inner material mainly consist of suberin, whereas the inner layer and compound middle lamella consist of lignin, cellulose, and other polysaccharides. We hypothesized a hierarchical model of the birch cork cell wall. The lignified cell wall with helical arrangement of cellulose microfibrils is sandwiched between suberized outer layer and inner material. Cellulose microfibrils in the inner layer bear tensile loads. In the wet state, water and cellulose transfer tensile stress. In the dried state, this stress-transferal system functions poorly and fewer cells bear stress. Suberin in the outer layer and inner material may prevent absolute drying to maintain mechanical properties of the bark and to bear tensile stress caused by trunk diameter growth.

Revealing the topochemical and structural changes of poplar lignin during a two-step hydrothermal pretreatment combined with alkali extraction

Lignin is an underutilized renewable resource in nature because of its complex structure and special distribution in plant cell walls. The proposal of an efficient treatment and the reveal of the structural characteristics of the isolated lignin are considerably important for the sustainable valorization of lignin. In this work, a two-step of hydrothermal pretreatment combined with alkali extraction was assembled into an integrated treatment and performed to extract lignin from poplar. The yield, purity, and structural changes of the lignin isolated from different treatment conditions were comparatively investigated. Results showed that 71.8 % of lignin with ultra-high purity was isolated during the integrated treatment at 180 °C. Confocal Raman microscopy demonstrated that the delignification occurred preferentially in the secondary wall (SW) and compound middle lamella (CML), and then in the whole morphological regions of the cell wall during the integrated treatment. NMR results revealed that the cleavage of β-O-4 linkages was dominant among the various reactions, which resulted in the increase of phenolic hydroxyl groups, the decrease of molecular weight, and the heterogeneity of the isolated lignin. However, the condensation of lignin became more serious with the increase of hydrothermal pretreatment temperature. These findings provide new insights for the separation and sustainable utilization of lignin for industries.

Characterisation of compound middle lamella isolated by a combination of wet-beating, sedimentation, and methanol dialysis

Abstract A simple method was developed to isolate the compound middle lamella (CML) in its natural state using wet-beating, sedimentation, and methanol dialysis. The isolated CML fraction was characterised. The CML was isolated in 2.0% yield from the mature wood of Ginkgo biloba. Scanning electron microscopy (SEM) images of the isolated CML fraction showed the presence of flake-like structures. However, some small amounts of secondary wall substance was observed. The lignin content of the CML fraction was approximately 45%. Thioacidolysis reactions with the isolated CML fraction revealed that the lignin β-O-4 structure was scarce in the isolated fraction and that numerous structures with two or more consecutive condensed-type bonds were present. Results from the solid-state carbon-13 nuclear magnetic resonance (13C NMR) experiments indicated that the CML fraction had low crystallinity, indicating low cellulose content. Liquid-state NMR analysis of the lignin from the CML fraction revealed the absence of p-hydroxyphenyl (H) units.

Visualizing plant cell wall changes proves the superiority of hydrochloric acid over sulfuric acid catalyzed γ-valerolactone pretreatment

Thermochemical pretreatment is one of the key steps to process lignocellulosic biomass for production of biofuels and biomaterials. γ-valerolactone (GVL) has been used as a green and renewable solvent to efficiently dissolve lignin under acidic conditions and enhance subsequent enzyme digestibility. Further improvement is still required to lower the pretreatment temperature in order to reduce sugar degradation and irreversible lignin condensation, as well as the capital cost. In this study, we compared the use of HCl and H2SO4 as catalysts during GVL pretreatment, and found the performance of GVL-HCl at 100 °C was comparable to that of GVL-H2SO4 at 120 °C in terms of xylan and lignin removal and enzyme digestibility. We further monitored the lignin removal and cellulose accessibility in the cell walls at different pretreatment time points by imaging the changes in lignin auto-fluorescence and in CtCBM3-GFP binding with confocal laser scanning microscopy (CLSM), respectively. We found GVL-HCl pretreatment at a relative low temperature (100 °C) could rapidly remove lignin in the compound middle lamella and cell corner areas, which concurred with the increase of CtCBM3-GFP binding in these areas. Real-time imaging of cell wall degradation by cellulases further revealed that the secondary cell walls could be digested from both cell lumen and CML sides, and eventually fully deconstructed within 24 h. Our results provide new insight into the effects of chloride anions on plant cell wall structure during GVL pretreatment, and offer potential routes to further optimize and enhance the efficiency of GVL-based pretreatment.