Introduction to forest genetics.

Lignin is a major component of wood, the most widely used raw material for the production of pulp and paper. Although the biochemistry and molecular biology underpinning lignin production are better understood than they are for the other wood components, recent work has prompted a number of re-evaluations of the lignin biosynthetic pathway. Some of the work on which these revisions have been based involved the investigation of transgenic plants with modified lignin biosynthesis. In addition to their value in elucidating the lignin biosynthetic pathway, such transgenic plants are also being produced with the aim of improving plant raw materials for pulp and paper production. This review describes how genetic engineering has yielded new insights into how the lignin biosynthetic pathway operates and demonstrates that lignin can be improved to facilitate pulping. The current technologies used to produce paper are presented in this review, followed by a discussion of the impact of lignin modification on pulp production. Fine-tuned modification of lignin content, composition, or both is now achievable and could have important economic and environmental benefits.

Lignin: Genetic Engineering and Impact on Pulping

Microfibril angle (MFA) is perhaps the easiest ultrastructural variable to measure for wood cell walls, and certainly the only such variable that has been measured on a large scale. Because cellulose is crystalline, the MFA of the S2 layer can be measured by X-ray diffraction. Automated X-ray scanning devices such as SilviScan have produced large datasets for a range of timber species using increment core samples. In conifers, microfibril angles are large in the juvenile wood and small in the mature wood. MFA is larger at the base of the tree for a given ring number from the pith, and decreases with height, increasing slightly at the top tree. In hardwoods, similar patterns occur, but with much less variation and much smaller microfibril angles in juvenile wood. MFA has significant heritability, but is also influenced by environmental factors as shown by its increased values in compression wood, decreased values in tension wood and, often, increased values following nutrient or water supplementation. Adjacent individual tracheids can show moderate differences in MFA that may be related to tracheid length, but not to lumen diameter or cell wall thickness. While there has been strong interest in the MFA of the S2 layer, which dominates the axial stiffness properties of tracheids and fibres, there has been little attention given to the microfibril angles of S1 and S3 layers, which may influence collapse resistance and other lateral properties. Such investigations have been limited by the much greater difficulty of measuring angles for these wall layers. MFA, in combination with basic density, shows a strong relationship to longitudinal modulus of elasticity, and to longitudinal shrinkage, which are the main reasons for interest in this cell wall property in conifers. In hardwoods, MFA is of more interest in relation to growth stress and shrinkage behaviour.

/pdf/microfibril-angle-measurement-variation-and-relationships-a-524gkdmy8w.pdf

Microfibril Angle: Measurement, Variation and Relationships – A Review

As the attraction of creating biofuels and bio-based chemicals from lignocellulosic biomass has increased, researchers have been challenged with developing a better understanding of lignin structure, quantity and potential uses. Lignin has frequently been considered a waste-product from the deconstruction of plant cell walls, in attempts to isolate polysaccharides that can be hydrolyzed and fermented into fuel or other valuable commodities. In order to develop useful applications for lignin, accurate analytical instrumentation and methodologies are required to qualitatively and quantitatively assess, for example, what the structure of lignin looks like or how much lignin comprises a specific feedstock׳s cellular composition. During the past decade, various diverse strategies have been employed to elucidate the structure and composition of lignin. These techniques include using two-dimensional nuclear magnetic resonance to resolve overlapping spectral data, measuring biomass with vibrational spectroscopy to enable modeling of lignin content or monomeric ratios, methods to probe and quantify the linkages between lignin and polysaccharides, or refinements of established methods to provide higher throughput analyses, less use of consumables, etc. This review seeks to provide a comprehensive overview of many of the advancements achieved in evaluating key lignin attributes. Emphasis is placed on research endeavored in the last decade.

Recent innovations in analytical methods for the qualitative and quantitative assessment of lignin

http://digital.csic.es/bitstream/10261/34812/3/2005-DELRIO-JAAP.pdf

Determining the influence of eucalypt lignin composition in paper pulp yield using Py-GC/MS

Relationships between cell and pulp properties were investigated by examining the within-tree property variations in Eucalyptus camaldulensis and Eucalyptus globulus. Properties investigated included proportions of ray and axial parenchyma, thickness of cell walls and cell wall percentages. The characteristics of the ray and axial parenchyma (their proportions and wall thickness) were found to have a significant influence on all measured pulp properties, including paper strength properties. Multiple regression of pulp properties in relation to cell properties revealed that nearly all measured pulp properties were explained by cell properties at the 1% significance level. It was concluded, therefore, that all cell types are important for predicting pulp properties, and it is strongly recommended that tree breeding programs for Eucalyptus include the measurement of all cell types.

Investigation of relationships between cell and pulp properties in Eucalyptus by examination of within-tree property variations

The feasibility of using FT-Raman spectroscopy for rapid non-destructive determination of lignin syringyl/guaiacyl (S/G) monomeric composition was examined using Eucalyptus camaldulensis and E. globulus, including samples of various ages and colors, which are of importance as a plantation source. The application of 2nd derivatives transformation of Raman spectroscopic data revealed highly significant correlations between wet chemical and Raman predicted values with correlation coefficient (r) = 0.998 and standard error of prediction (SEP) < 0.07 points in the calibration (for known samples), and r = 0.935 and SEP < 0.32 points in the prediction (for unknown samples), respectively. Consequently, this nondestructive method has proved its validity for analyzing Eucalyptus native wood meal samples, regardless of their age and color to determine lignin S/G monomeric composition. Using FT-Raman spectroscopy, elite tree selection based on quality aspects for pulp and paper production can be performed.

Non-destructive determination of lignin syringyl/guaiacyl monomeric composition in native wood by Fourier transform Raman spectroscopy

The feasibility of using FT-Raman spectroscopy for rapid determination of various wood constituents non-destructively was examined using five Eucalyptus species, including samples of various ages and colors of samples, which are of importance as a plantation source. Wood constituents which relate to pulp properties (holocellulose, α -cellulose, hemicellulose, lignin, extractives, alkali-extractives, total-extractives, and extractives-free (EF) wood constituents for holocellulose, α -cellulose, hemicellulose and lignin) were measured. The application of 2nd derivatives transformation of Raman spectroscopic data revealed highly significant correlations between wet chemical and Raman predicted values for all traits except EF-hemicellulose, with standard error of prediction (SEP) < 0.8 points in the calibration (for known samples) and SEP < 3.4 points in the prediction (for unknown samples), respectively. Consequently, this non-destructive method has proved its validity for analyzing various Eucalypt...

Non-destructive Determination of Wood Constituents by Fourier Transform Raman Spectroscopy

Chemical and anatomical characterization of the tension wood of Eucalyptus camaldulensis L

Relationship between various extracted basic densities and wood chemical components were investigated by their within-tree variations inEucalyptus camaldulensis for assistance in the prediction of the properties of wood or wood derived products. Within-tree variation was not observed for basic density because extraneous compounds masked it. However, extractives-free basic density, total extractives-free basic density and extraneous compounds-free basic density were high on the bark side and top parts in the trunk. These extracted basic densities were expected to have significant relationships to the fiber morphology causing the within-tree variations, and to be very important factors for wood industries. These relationships were sought by correlations between extracted basic densities and wood chemical components based on their within-tree variations. Furthermore, fair relationships between extracted basic densities and hemicellulose composition were observed and speculation made as to the relationship to the constituent ratio of cell wall layers.

Kazuya Ito

Papers

Investigation of relationships between cell and pulp properties in Eucalyptus by examination of within-tree property variations

Non-destructive determination of lignin syringyl/guaiacyl monomeric composition in native wood by Fourier transform Raman spectroscopy

Non-destructive Determination of Wood Constituents by Fourier Transform Raman Spectroscopy

Chemical and anatomical characterization of the tension wood of Eucalyptus camaldulensis L

Relationship between various extracted basic densities and wood chemical components in Eucalyptus camaldulensis