Lignin Distribution In Cell Wall Research Articles

Determining the lignin distribution in plant fiber cell walls based on chemical and biological methods

Cellulosic fibers are widely used in biocomposites, paper and paperboard products, and other fiber-based materials. The properties of fiber-based materials are significantly affected by lignin characteristics, especially the lignin distribution in cellulosic fiber cell walls. In this study, chemical (sodium chlorite) and biological (laccase/mediator system) techniques were used to control three fiber models with different lignin contents at about 20%, 10%, 5%, respectively. The lignin distribution in cell walls was determined based on the “enzymatic peeling” method and SEM–EDS analysis. Results showed that the lignin concentrations in fiber cell walls prepared from the combined chemical and biological techniques were lower in the outer region and higher in the inner region than those from the chemical treatment only, which is due to the fact that laccase-induced lignin degradation is only limited to the outer region and not able to get into the inner region. The fiber model with less lignin in the inner region of the cell wall had a better deformation performance (the flexibility of 1.559 × 109 N−1 m−2) than that with more lignin in the same region. The relationships of fiber models of different specific lignin distribution with their deformability were established, which could be valuable to extend the wide value-added applications of fiber-based materials.

Effect of constituents molar ratios of deep eutectic solvents on rice straw fractionation efficiency and the micro-mechanism investigation

Effective obtaining fermentable sugars and other platform chemicals from rice straw mediated by choline chloride- oxalic acid dihydrate (CO) and the corresponding micro-mechanism investigation were conducted in this work. Choosing a suitable constituents molar ratio of CO appeared to be a feasible method to achieve an appropriate pretreatment severity for a good biomass fractionation. Pretreatment by using CO with high oxalic acid dihydrate to choline chloride molar ratio could afford easily digestible cellulose-rich materials (CMRs, >80% of enzymatic digestion) and lignin-rich materials (LRMs) of high purity (>82%) due to extensive hemicellulose removal (>93%) and delignification (around 70%). Cell wall microstructure characterizations based on confocal laser scanning microscopy (CLSM) and transmission electron microscopy (TEM) verified the stronger xylan and lignin removal ability of CO with higher oxalic acid dihydrate content. Moreover, the considerable removal of xylan confirmed by CLSM was beneficial to delignification and the subsequent cellulose enzymatic hydrolysis. Furthermore, ultra-structural changes of lignin distribution in cell walls based on TEM indicated the occurrence of partial delignification, preferentially in cell corner (CC) and compound middle lumen (CML) rather than in the secondary cell walls. These findings provides a new insight into the detailed mechanism of acidic DESs mediated biomass deconstruction.

Characterization of anatomy, ultrastructure and lignin microdistribution in Forsythia suspensa

Forsythia suspensa, as a traditional Chinese medicinal herb, has been studied extensively. In this work, morphological and anatomical features of F. suspensa stem were examined by light microscopy (LM) and scanning electron microscopy (SEM). The results showed that the slenderness and Runkel ratio is 51 and 0.67, respectively. Anatomical observations indicated that F. suspensa is diffuse-porous wood. Helical thickenings and alternate intervessel pits are present on vessel cell wall. Transmission electron microscopy (TEM) images exhibited that the fiber cell wall is typically differentiated into three layers: middle lamella (ML), primary wall (P) and secondary wall (S1, S2 and S3), and the staining intensities represent differing lignin concentrations. Also, the confocal laser scanning microscopy (CLSM) and scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDXA) were used to investigate the lignin distribution in cell wall qualitatively and semi-quantitatively. Confocal images (488nm) revealed a high level of lignin autofluorescence in the cell corner middle lamella (CCML), with lower levels of fluorescence in the compound middle lamella (CML) and S2 region. The results from SEM-EDXA demonstrated that lignin concentration ratio in different regions of fiber wall is 1.3 (CCML):1.1 (CML):1 (S2).

Combined histochemistry and autofluorescence for identifying lignin distribution in cell walls

Histological staining methods commonly used for detecting cellulose and lignin in cell walls were combined with epifluorescence microscopy to visualize differences in lignification between and within cellular elements. We tested our approach on sections of one-year-old branches of Fraxinus ornus L., Myrtus communis L., Olea europaea L., Pistacia lentiscus L. and Rhamnus alaternus L., containing both normal and tension wood. Sections were subjected to various staining techniques, viz. safranin O, safranin O/fast green FCF, and alcoholic solutions of safranin O/astra blue, according to the commonly accepted protocols. Stained and unstained sections were compared using both light and epifluorescence microscopy. Safranin O with or without counterstaining hid the strong fluorescence of vessel walls, cell corners and middle lamellae allowing the secondary wall fibers to fluoresce more clearly. Epifluorescence microscopy applied to stained sections showed more cell wall details than autofluorescence of unstained sections or white light microscopy of counterstained sections. This simple approach proved reliable and valuable for detecting differences in lignification in thick sections without the need for costly equipment.

Anatomy, ultrastructure and lignin distribution in cell wall of Caragana Korshinskii

Anatomy and ultrastructure in cell wall of Caragana Korshinskii was examined by transmission electron microscopy (TEM). Lignin distribution was determined by using confocal laser scanning microscopy (CLSM) and transmission electron microscopy with energy dispersive X-ray analysis (TEM–EDXA). TEM images showed that cell wall of C. Korshinskii was typically divided into three layers including the primary wall (P), the middle lamellar (ML) and the secondary wall (S 1, S 2 and S 3). Confocal images (530 nm) of C. Korshinskii showed that strongly lignified CCML, and weakly lignified ML and S2 layer. Weakly lignified fibres (F) and strongly ligninfied vessels (V) were also detected by using CLSM. TEM–EDXA was applied to determine the lignin concentration in the cell corner of middle lamellar (CCML), compound middle lamellae (CML) and S 2 layer. Results obtained from confocal microscopy were further confirmed by using TEM–EDXA, indicating that the ratio of lignin concentration in CCML, ML and S2 is 1.5:1.2:1.

Lignin distribution in wood cell walls determined by TEM and backscattered SEM techniques

The lignin distribution in cell walls of spruce and beech wood was determined by high-voltage transmission-electron-microscopy (TEM) in sections stained with potassium permanganate as well as by field-emission-scanning-electron-microscopy (FE-SEM) combined with a back-scattered electron detector on mercurized specimens. The latter is a new technique based on the mercurization of lignin and the concomitant visualization of mercury by back-scattered electron microscopy (BSE). Due to this combination it was possible to obtain a visualized overview of the lignin distribution across the different layers of the cell wall. To our knowledge, this combined method was used the first time to analyse the lignin distribution in cell walls. In agreement with previous work the highest lignin levels were found in the compound middle lamella and the cell corners. Back-scattered FE-SEM allows the lignin distribution in the pit membrane of bordered pits as well as in the various cell wall layers to be shown. In addition, by using TEM as well as SEM we observed that lignin closely follows the cellulose microfibril orientation in the secondary cell wall. From these observations, we conclude that the polymerisation of monolignols is affected by the arrangement of the polysaccharides which constitute the cell wall.

Lignin distribution in wood from a progeny trial of genetically selected Pinus radiata D. Don

Cell wall lignin distribution was assessed in Pinus radiata wood using quantitative interference microscopy. Three groups of trees were examined. Five trees, offspring of NZ clone 850-55, and five trees of NZ 850-55 crossed with several parents of the Guadelupe provenance, were compared with five trees of unselected P. radiata. Lignin concentration in the cell corner middle lamella region was significantly lower in both offspring groups of NZ 850-55 when compared with the unselected control trees. No difference in S2 lignin concentration was observed among the three groups. This result represents the first indication that variations in lignin distribution are genetically controlled in pines.

Lignin Distribution in Cell Walls of Birch Wood Decayed by White Rot Basidiomycetes

Lignin Distribution in Cell Walls of Birch Wood Decayed by White Rot Basidiomycetes