Explore the vast range of titles available.

Cell death plays an important role in the determination of secondary xylem cell functions. Tracheary elements (TEs), such as vessel elements and tracheids, lose their organelles due to rapid autolysis after the completion of secondary wall thickening and lignification, and play an important role in water movement along the stem. In contrast, xylem axial and ray parenchyma cells (xylem parenchyma cells) remain alive for several years or longer and retain their organelles even after maturation. As a result, xylem parenchyma cells play important roles in nutrient storage, axial and radial transportation of materials, and defense responses in the stem. In addition, they are involved in the formation of heartwood, which contributes to increases in the resistance of the tree trunk to decay, as they synthesize heartwood components such as polyphenols prior to their death. The present review focuses on changes in long-lived ray parenchyma cells during heartwood formation, such as morphology and contents of organelles, gene expression, and survival rate in sapwood. This review also summarizes the differences in cell death characteristics between TEs and ray parenchyma cells. The elucidation of the cell death mechanism of ray parenchyma cells is expected to provide useful information for controlling the properties of heartwood.

We prepared 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized samples from never-dried Japanese cedar (JC) holocellulose, JC-callus, and bacterial cellulose (BC). The original never-dried samples and their TEMPO-oxidized products were characterized by neutral sugar composition analysis. TEMPO-oxidized cellulose nanofibrils (TEMPO-CNFs) were prepared from the TEMPO-oxidized samples by ultrasonication in water. The carboxy groups in TEMPO-CNFs were position-selectively esterified with 9-anthryl diazomethane (ADAM) to prepare TEMPO-CNF-COOCH2-C14H9 samples, which had UV absorption peak at 365 nm. The mass-average degree of polymerization (DPw) values of 1% lithium chloride/N,N-dimethylacetamide (LiCl/DMAc) solutions of the original samples were determined by size-exclusion chromatography in combination with multi-angle laser-light scattering, ultraviolet absorption, and refractive index detection (SEC/MALLS/UV/RI), and were 5490, 2660, and 2380 for the JC holocellulose, JC-callus, and BC samples, respectively. The TEMPO-CNF-COOCH2-C14H9 sample solutions in 1% LiCl/DMAc were analyzed by SEC/MALLS/UV/RI to obtain SEC elution patterns. The patterns corresponded to the molar mass and carboxy group distributions of the samples, which were detected by RI and UV absorption of anthryl groups, respectively. The carboxy groups existed in the entire molar mass distribution regions of all the TEMPO-CNF samples, although their lower molar mass regions contained higher carboxy group densities. The obtained results indicate that random depolymerization occurred on the cellulose microfibril surfaces at the initial stage of TEMPO-catalyzed oxidation and/or ultrasonication in water. This depolymerization mechanism can explain all the obtained SEC-elution patterns of the TEMPO-CNFs, without considering the presence of periodically disordered regions in the cellulose microfibrils of the never-dried cellulose samples.

The secondary tissues of woody plants consist of fragile cells and rigid cell walls. However, the structures are easily damaged during mechanical cross-sectioning for electron microscopy analysis. Broad argon ion beam (BIB) milling is commonly employed for scanning electron microscopy (SEM) of hard materials to generate a large and distortion-free cross-section. However, BIB milling has rarely been used in plant science. In the present study, SEM combined with BIB milling was validated as an accurate tool for structural observation of secondary woody tissues of two samples, living pine ( Pinus densiflora ) and high-density oak wood ( Quercus phillyraeoides ), and compared with classical microtome cross-sectioning. The BIB milling method does not require epoxy resin embedding because of prior chemical fixation and critical point drying of the sample, thus producing a three-dimensional image. The results showed that xylem structures were well-preserved in their natural state in the BIB-milled cross-section compared with the microtome cross-section. The observations using SEM combined with BIB milling were useful for wide-area imaging of both hard and soft plant tissues, which are difficult to observe with transmitted electron microscopy because it is difficult to obtain sections of such tissues, particularly those of fragile reaction woods.

Structural control is essential for further development of cellulosic materials. Here, we demonstrated the significance of the orientation and degree of polymerization in the integrated structure of cellulose microfibrils using sheets based on the hierarchical structure of wood. Non-cellulosic components were removed from wood blocks of a conifer by applying a two-step chemical treatment. Partially changing the treatment conditions generated cellulose blocks with varying degrees of polymerization while maintaining the anatomical structure. Cellulose sheets with oriented microfibrils were subsequently prepared by heat-pressing the blocks. Sheets with randomized appearance of orientation were also produced by disassembling tracheid alignment. These sheets were then subjected to structural evaluation and tensile tests. Comparison of both sheets showed that microfibril orientation mainly determined the modulus. As long as the orientation was maintained, the specific modulus was independent of the degree of polymerization. In contrast, the tensile strength of the oriented sheet varied with the degree of polymerization, indicating that it notably reflected the single fiber strength compared to the randomly oriented sheet. Hence, a highly oriented structure with unfragmented microfibrils is the determinant of a superior material. Consequently, the sheets in which these parameters are readily controlled can advance cellulose applications. Graphic abstract

This study reports on the preparation of lignin-free wood sections maintaining the anatomical structure of Cryptomeria japonica by means of alcoholysis combined with sodium chlorite treatment. To determine the optimal alcoholysis conditions, Fourier transform infrared spectroscopy was combined with multivariate analysis, and the obtained results indicated that the alcoholysis reaction proceeded over three stages. In the first stage, lignin and hemicellulose are partially removed. In the second stage, hemicellulose and amorphous cellulose are degraded and humin is formed. In the third stage, crystalline cellulose is degraded, further promoting the formation of humin. Since it is difficult to completely remove lignin by alcoholysis alone, the wood sections were subsequently subjected to sodium chlorite treatment. As a result, lignin-free sections were produced without degradation of the woody anatomical structure. Furthermore, alcoholysis at 140 °C for 1 h coupled with sodium chlorite treatment for 1 h succeeded in producing sections composed of essentially hemicellulose-free cellulose. These achievements make this protocol potentially applicable as a substrate for artificial cell walls and for the development of novel functional filters.

Wood products function as carbon storage even after being harvested from forests. This has garnered attention in relevance to climate change countermeasures. In the progress of efforts toward climate change mitigation by private companies, the effective use of wood products has been an important measure. However, the methodology for accounting carbon stocks in wood products for private companies has not been established. Therefore, this study investigated methods for estimating carbon stocks in wood products used in wooden houses built by private enterprises, targeting a major company in the Japanese building industry. The results indicated that both the direct inventory method and flux data method (FDM) were applicable for estimating the carbon stocks. These two methods use data that can be obtained from many other building companies, thus, indicating high versatility. The log-normal, Weibull, normal, and logistic distributions, in descending order, proved to be suitable lifetime functions of wooden houses under the FDM, with a half-life of 66–101 years. It is important to continuously acquire time-series data on the floor areas of both newly built and existing houses and the amount of wood products used to improve the accuracy of estimates and explore future predictions.

Lignin-free wood has been successfully developed via a two-step chemical treatment while maintaining its inherent hierarchical structure. The first step was alcoholysis which was conducted using ethylene glycol, and whose condition was optimized by monitoring the removal of lignin using infrared spectroscopy. The second step was bleaching wherein the delignification proceeded from the surface to the core of the wood block, and finally resulted in complete decolorization. Although the wood block was free from lignin and hemicellulose as approximately confirmed by the chemical composition analysis, the 3-dimensional colorless wood block was almost unaltered, even after freeze–drying. Then, multidirectional observation was performed to investigate whether the natural hierarchical structure from anatomical- to nano-level was maintained. Optical microscopy, X-ray microcomputed tomography, X-ray diffractometry, and transmission electron microscopy demonstrated that all the stages of hierarchical structure were maintained. The lignin-free wood block has great potential for novel materials that are supported by a 3-dimensional wooden architecture. The derived lignin-free wood is also a suitable specimen that can be used to understand the formation and functionality of the anatomical structure and lignified cell wall.

Main conclusion 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.

Abstract Investigating plant structure is fundamental in botanical science and provides crucial knowledge for the theories of plant evolution, ecophysiology and for the biotechnological practices. Modern plant anatomy often targets the formation, localization and characterization of cellulosic, lignified or suberized cell walls. While classical methods developed in the 1960s are still popular, recent innovations in tissue preparation, fluorescence staining and microscopy equipment offer advantages to the traditional practices for investigation of the complex lignocellulosic walls. Our goal is to enhance the productivity and quality of microscopy work by focusing on quick and cost-effective preparation of thick sections or plant specimen surfaces and efficient use of direct fluorescent stains. We discuss popular histochemical microscopy techniques for visualization of cell walls, such as autofluorescence or staining with calcofluor, Congo red (CR), fluorol yellow (FY) and safranin, and provide detailed descriptions of our own approaches and protocols. Autofluorescence of lignin in combination with CR and FY staining can clearly differentiate between lignified, suberized and unlignified cell walls in root and stem tissues. Glycerol can serve as an effective clearing medium as well as the carrier of FY for staining of suberin and lipids allowing for observation of thick histological preparations. Three-dimensional (3D) imaging of all cell types together with chemical information by wide-field fluorescence or confocal laser scanning microscopy (CLSM) was achieved. Investigating plant structure is fundamental in botanical science. Across disciplines, such as plant development, ecophysiology and biotechnology, particular interest is focused on the complex structure of lignocellulosic walls. We review the recent innovations in tissue preparation and fluorescence staining for lignin and suberin. We demonstrate simple and cost-effective protocols for preparation of plant samples for microscopy using hand-cut sections and clearing with glycerol. Autofluorescence of lignin in combination with direct stains such as Congo red and fluorol yellow can clearly differentiate between lignified, suberized and unlignified cell wall domains.

Key message A better understanding of the influence of environmental conditions on wood formation should help to improve the radial growth of trees and to prepare for climate change. The cambial activity of trees is associated with seasonal cycles of activity and dormancy in temperate zones. The timing of cambial reactivation in early spring and dormancy in autumn plays an important role in determination of the cambial growth and the environmental adaptivity of temperate trees. This review focuses on the temperature regulation of the timing of cambial reactivation and xylem differentiation and highlights recent advances of bud growth in relation to cambial activity of temperate trees. In addition, we discuss relationships between the timing of cambial reactivation, start of xylem differentiation and changes in levels of storage materials to identify the source of the energy required for cell division and differentiation. We also present a summary of current understanding of the effects of rapid increases and decreases in temperature on cambial activity, by localized heating and cooling, respectively. Increases in temperature from late winter to early spring influence the physiological processes that are involved in the initiation of cambial reactivation and xylem differentiation both in localized heated stems and under natural conditions. Localized cooling has a direct effect on cell expansion, the thickening of walls of differentiating tracheids, and the rate of division of cambial cells. A rapid decrease in temperature of the stem might be the critical factor in the control of latewood formation and the cessation of cambial activity. Therefore, temperature is the main driver of cambial activity in temperate trees and trees are able to feel changes in temperature through the stem. The climate change might affect wood formation in trees.