Cellulose and lignin biosynthesis is altered by ozone in wood of hybrid poplar (Populus tremula × alba)

Wood formation in trees is a dynamic process that is strongly affected by environmental factors. However, the impact of ozone on wood is poorly documented. The objective of this study was to assess the effects of ozone on wood formation by focusing on the two major wood components, cellulose and lignin, and analysing any anatomical modifications. Young hybrid poplars (Populus tremula × alba) were cultivated under different ozone concentrations (50, 100, 200, and 300 l l(-1)). As upright poplars usually develop tension wood in a non-set pattern, the trees were bent in order to induce tension wood formation on the upper side of the stem and normal or opposite wood on the lower side. Biosynthesis of cellulose and lignin (enzymes and RNA levels), together with cambial growth, decreased in response to ozone exposure. The cellulose to lignin ratio was reduced, suggesting that cellulose biosynthesis was more affected than that of lignin. Tension wood was generally more altered than opposite wood, especially at the anatomical level. Tension wood may be more susceptible to reduced carbon allocation to the stems under ozone exposure. These results suggested a coordinated regulation of cellulose and lignin deposition to sustain mechanical strength under ozone. The modifications of the cellulose to lignin ratio and wood anatomy could allow the tree to maintain radial growth while minimizing carbon cost.     

腐烂等级、径级对典型阔叶红松林红松倒木物理化学性质的影响

倒木是森林生态系统的重要组成部分, 在地力维护、生物多样性保持以及碳(C)和养分循环等方面具有重要意义, 但倒木物理化学性质随其腐烂等级和径级而变化。为了深入理解腐烂等级和径级对倒木物理化学性质的影响, 该研究以典型阔叶红松林的建群种——红松(Pinus koraiensis)的倒木为研究对象, 将其每个腐烂等级(I-V)下的倒木分为4个径级(径级i ≤ 10.0 cm、径级ii 10.1-30.0 cm、径级iii 30.1-50.0 cm、径级iv >50.0 cm), 研究了不同腐烂等级、径级及两者交互作用对倒木心材和边材物理化学性质的影响。结果表明: 心材和边材具有相似的变化规律。倒木心材和边材含水率随着腐烂等级增加而增加, 而木材密度随腐烂等级和径级的增加均呈下降趋势; 边材C含量以及心材和边材的氮(N)、磷(P)含量随腐烂等级增加呈上升趋势, 心材N、P含量随径级增加呈先增加后减少的趋势; 纤维素含量随腐烂等级增加呈下降趋势, 而木质素含量呈上升趋势, 纤维素和木质素含量随径级增加没有明显变化规律。倒木含水率与C、N、P、木质素含量(除心材P含量)显著正相关, 与纤维素含量显著负相关; 木材密度与C、N、P、木质素含量显著负相关, 与纤维素含量显著正相关。由此可见, 倒木物理化学性质受不同腐烂等级和径级的影响有各自的变化规律, 且倒木的物理性质(含水率和木材密度)是影响化学含量变化的重要因素。     

Effects of decay classes and diameter classes on physico-chemical properties of Pinus koraiensis log in a typical mixed broadleaved-Korean pine forest

AimsLog is an important component for most of forest ecosystems. It plays crucial roles in maintaining soil fertility, sustaining biodiversity and cycling of carbon (C) and nutrient. However, physico-chemical properties of logs vary with decay classes and diameter classes. Our objective was to study effects of decay classes and diameter classes on physico-chemical properties of logs in a typical mixed broadleaved-Korean pine forest in northern China.MethodsIn this study, logs of Pinus koraiensis were chosen as it was the constructive species in the typical mixed broadleaved-Korean pine forest. Logs of P. koraiensis at each decay classes (I-V) were divided into four diameter classes, including diameter class i ≤ 10.0 cm, diameter class ii: 10.1-30.0 cm, diameter class iii: 30.1-50.0 cm, and diameter class iv > 50.0 cm. Then, we explored effects of different decay classes, diameter classes and their interactions on the physico-chemical properties of logs for both the heartwood and sapwood.Important findings The results showed that the physico-chemical properties of heartwood and sapwood generally exhibited similar variations. Their moisture content both increased with an increasing decay class, whereas wood density both decreased with an increased decay class and diameter class. The carbon concentrations of the sapwood showed a trend of gradual increasing during decomposition, and there was an accumulation in nitrogen (N) and phosphorus (P) concentrations of the heartwood and sapwood with an increased decay class, simultaneously. Only N and P concentrations of the heartwood increased and then decreased with an increasing diameter class. The cellulose content decreased with an increasing decay class. In contrast to the cellulose, the lignin content increased with an increased decay class. However, cellulose and lignin contents exhibited no distinct trend among diameter classes. The moisture content of logs had a significant positive correlation with C, N, P concentrations and lignin content (except P concentrations of the heartwood), but had a significant negative correlation with the cellulose content (p< 0.05). The wood density was negatively correlated with C, N, P concentrations and the lignin content, but it was positively correlated with the cellulose content (p< 0.05). Therefore, physico-chemical properties of logs had unique patterns along both decay classes and diameter classes, and the physical properties of logs (the moisture content and wood density) were important factor affecting the variations of their chemical contents.     

QTL Mapping of Wood FT-IR Chemotypes Shows Promise for Improving Biofuel Potential in Short Rotation Coppice Willow (<Emphasis Type="Italic">Salix</Emphasis> spp.)

An increasing interest to convert lignocellulosic biomass into biofuels has highlighted the potential of using willows for this purpose, due to its fast growth in short rotation coppice systems. Here, we use a mapping population of 463 individuals of a cross between Salix viminalis and S. viminalis × S. schwerinii to investigate the genetic background of different wood chemical traits, information of importance for breeding towards different uses of wood. Furthermore, using a subset of the mapping population, the correlation between biogas production and chemical traits was investigated. The phenotyping of wood was carried by Furrier-transformed-Infrared spectrometry (FT-IR) and water content analysis. Quantitative trait loci (QTLs) analysis was used to identify regions in the genome of importance for the phenotypic variation of these chemical traits. We found 27 QTLs for various traits. On linkage group (LG) VI-1, QTLs for signals assigned to G-lignin, lignin, and the S/G ratio were collocated and on LG XIV we found a cluster of QTLs representing signals assigned to lignin, cellulose, hemicellulose, and water. The QTLs explained from 3.4 to 6.9% of the phenotypic variation indicating a quantitative genetic background where many genes influence the traits. For the biogas production, a positive and negative correlation was seen with the signals assigned to acetyl and lignin, respectively. This study represents a first step in the understanding of the genetic background of wood chemical traits for willows, information needed for complementary studies, mapping of important genes, and for breeding of varieties for biofuel production purposes.     

Genetic variation in Eucalyptus nitens pulpwood and wood shrinkage traits

Eucalyptus nitens plantations are generally established for pulpwood production but an increasing area is being managed for solid wood. Genetic variation in, and correlations among, three Kraft pulpwood traits (diameter at breast height, basic density and near-infrared-predicted cellulose content) and three 12-mm wood-core shrinkage traits (recoverable collapse, net shrinkage and gross shrinkage) were examined, utilising data from two 9-year-old first-generation progeny trials in Tasmania. These trials contained approximately 400 open-pollinated families (over 100 of which were sampled for wood properties) representing three central-Victorian E. nitens races. Significant genetic variation at the race and/or within-race level was identified in all traits. Within races, relative levels of additive genetic variation were higher for shrinkage traits, although narrow-sense heritabilities were lower and the expression of genetic variation less stable across sites than for other wood property traits. Heterogeneous intertrait genetic correlations were identified across sites between growth and some wood property traits. However, where significant, genetic correlations indicated that within-race selection for growth would adversely affect core basic density and all core shrinkage traits. Furthermore, results based on cores suggested that within-race selection for higher basic density would favourably impact on cellulose content and collapse but selection for either higher basic density or cellulose content would adversely affect net shrinkage. Most within-race genetic variation in gross shrinkage appeared to be due to genetic variation in collapse. The implications of these results for sawn timber breeding will depend on the strength of genetic correlations between core traits and rotation-age objective traits and objective trait economic weights.     

Structural Alterations of Lignins in Transgenic Poplars with Depressed Cinnamyl Alcohol Dehydrogenase or Caffeic Acid O-Methyltransferase Activity Have an Opposite Impact on the Efficiency of Industrial Kraft Pulping

We evaluated lignin profiles and pulping performances of 2-year-old transgenic poplar (Populus tremula × Populus alba) lines severely altered in the expression of caffeic acid/5-hydroxyferulic acid O-methyltransferase (COMT) or cinnamyl alcohol dehydrogenase (CAD). Transgenic poplars with CAD or COMT antisense constructs showed growth similar to control trees. CAD down-regulated poplars displayed a red coloration mainly in the outer xylem. A 90% lower COMT activity did not change lignin content but dramatically increased the frequency of guaiacyl units and resistant biphenyl linkages in lignin. This alteration severely lowered the efficiency of kraft pulping. The Klason lignin level of CAD-transformed poplars was slightly lower than that of the control. Whereas CAD down-regulation did not change the frequency of labile ether bonds or guaiacyl units in lignin, it increased the proportion of syringaldehyde and diarylpropane structures and, more importantly with regard to kraft pulping, of free phenolic groups in lignin. In the most depressed line, ASCAD21, a substantially higher content in free phenolic units facilitated lignin solubilization and fragmentation during kraft pulping. These results point the way to genetic modification of lignin structure to improve wood quality for the pulp industry.     

Tensile growth stress and lignin distribution in the cell walls of yellow poplar, Liriodendron tulipifera Linn.

Five specimens that contained a continuous gradient of wood, from normal to tension wood regions, were collected from an inclined yellow poplar (Liriodendron tulipifera), and the released strain of tensile growth stress was quantified. Ultraviolet (UV) microspectrophotometry was used to examine the relationship between lignin distribution in the cell wall and the intensity of tensile growth stress. The UV absorption of the secondary wall and the cell corner middle lamella decreased with increasing tensile released strain (i.e., tensile growth stress). The UV absorption in the compound middle lamella region remained virtually constant, irrespective of the tensile released strain. The absorption maximum (5_max) remained virtually constant in the secondary wall, the cell corner middle lamella, and the compound middle lamella region at 273-274, 277-278, and 275-278 nm respectively, irrespective of the tensile released strain. The ratios of the UV absorbance at 280 to 260 nm and 280 to 273 nm of the secondary wall decreased with increasing tensile released strain. The ratios in the cell corner and compound middle lamella region remained constant, irrespective of the tensile released strain. The lignin content of the secondary wall decreased, while the syringyl/guaiacyl ratio increased with increasing tensile released strain. Gelatinous fibers were not observed in the tension wood regions, but the secondary wall became gelatinous-layer-like, i.e., the lignin content and microfibrillar angle decreased and the cellulose content increased. A definite gelatinous layer seems to be important for generating greater tensile growth stress. It is concluded that a decrease in lignin and an increase in cellulose microfibrils parallel to the fiber axis in the secondary wall are necessary to produce large tensile growth stress.     

Genetic improvement of the chemical composition of Scots pine (Pinus sylvestris L.) juvenile wood for bioenergy production

Chemical composition is one of the key characteristics that determines wood quality and in turn its suitability for different end products and applications. The inclusion of chemical compositional traits in forest tree improvement requires high‐throughput techniques capable of rapid, non‐destructive and cost‐efficient assessment of large‐scale breeding experiments. We tested whether Fourier‐transform infrared (FTIR) spectroscopy, coupled with partial least squares regression, could serve as an alternative to traditional wet chemistry protocols for the determination of the chemical composition of juvenile wood in Scots pine for tree improvement purposes. FTIR spectra were acquired for 1,245 trees selected in two Scots pine (Pinus sylvestris L.) full‐sib progeny tests located in northern Sweden. Predictive models were developed using 70 reference samples with known chemical composition (the proportion of lignin, carbohydrates [cellulose, hemicelluloses and their structural monosaccharides glucose, mannose, xylose, galactose, and arabinose] and extractives). Individual‐tree narrow‐sense heritabilities and additive genetic correlations were estimated for all chemical traits as well as for growth (height and stem diameter) and wood quality traits (density and stiffness). Genetic control of the chemical traits was mostly moderate. Of the major chemical components, highest heritabilities were observed for hemicelluloses (0.43–0.47), intermediate for lignin and extractives (0.30–0.39), and lowest for cellulose (0.20–0.25). Additive genetic correlations among chemical traits were, except for extractives, positive while those between chemical and wood quality traits were negative. In both groups (chemical and wood quality traits), correlations with extractives exhibited opposite signs. Correlations of chemical traits with growth traits were near zero. The best strategy for genetic improvement of Scots pine juvenile wood for bioenergy production is to decrease and stabilize the content of extractives among trees and then focus on increasing the cellulose:lignin ratio.     

转UGPase基因喜树木材化学成分与生长速率研究

分析了田间栽培条件下2年生转UGPase基因喜树与对照株的木材化学成分与生长速率。结果表明,转UGPase基因喜树综纤维素含量达到78.87%,比对照株相比提高了2.23%;纤维素含量为36.34%,与对照株相比没有明显提高;木质素含量为15.05%,较对照株降低了1.75%;两者的灰分含量均较低且无显著差异;冷、热水抽提物含量为7.62%与10.17%,分别提高了2.04%与2.13%;1% NaOH抽提物含量为27.13%,提高了1.27%。因此,就综纤维素、木质素、灰分含量而言,转UGPase基因喜树为优质纸浆材,水抽提物和1% NaOH抽提物的含量略高,在纸浆生产中需加以重视。本文还对转UGPase基因喜树与对照株的株高、基径、生物量进行了动态监测,结果表明,从5月25日到11月10日的生长季中,其株高平均增加121 cm,对照株平均仅67.8 cm,株高生长速率提高了78.47%;基径平均增加1 792 cm,对照株平均仅0.532 8 cm,提高了236.37%;地上部分生物量的积累与对照相比提高了322.61%,即转入UGPase基因使喜树生长速率显著提高。因此,虽然转UGPase基因喜树的综纤维素和纤维素含量没有明显提高,但其生长速率快,生物量增长显著,间接提高了纤维素与喜树碱的产量。因此,转基因喜树较普通喜树更符合纸浆材速生、纤维素含量高和产量高、木质素含量低的基本要求,可在生产中进一步推广。     

QTL influencing growth and wood properties in Eucalyptus globulus

Regions of the genome affecting physical and chemical wood properties (quantitative trait loci (QTL)), as well as growth, were identified using a clonally replicated, outbred F₂ family (112 genotypes, each with two ramets) of Eucalyptus globulus, planted in a field trial in north-west Tasmania. Traits studied were growth (assessed by stem diameter), wood density, cellulose content, pulp yield and lignin content. These traits are important in breeding for pulpwood, and will be important in breeding for carbon sequestration and biofuel production. Between one and four QTL were located for each trait, with each QTL explaining between 4% and 12% of the phenotypic variation. Several QTL for chemical wood properties were co-located, consistent with their high phenotypic correlations, and may reflect pleiotropic effects of the same genes. In contrast, QTL for density and lignin content with overlapping confidence intervals were considered to be due to independent genes, since the QTL effects were inherited from different parents. The inclusion of fully informative microsatellites on the linkage map allowed the determination of homology at the linkage group level between QTL and candidate genes in different pedigrees of E. globulus and different eucalypt species. None of the candidate genes mapped in comparable studies co-located with our major QTL for wood chemical properties, arguing that there are important candidate genes yet to be discovered.     

Quantitative trait locus (QTL) analysis of wood quality traits in <Emphasis Type="Italic">Eucalyptus nitens</Emphasis>

To identify the chromosomal regions affecting wood quality traits, we conducted a genome-wide quantitative trait locus (QTL) analysis of wood quality traits in Eucalyptus nitens. This information is important to exploit the full potential of the impending Eucalyptus genome sequence. A three generational mapping population consisting of 296 progeny trees was used to identify QTL associated with several wood quality traits in E. nitens. Thirty-six QTL positions for cellulose content, pulp yield, lignin content, density, and microfibril angle (MFA) were identified across different linkage groups. On linkage groups (LG)2 and 8, cellulose QTL cluster with pulp yield and extractives QTL while on LG4 and 10 cellulose and pulp yield QTLs cluster together. Similarly, on LG4, 5, and 6 QTL for lignin traits were clustered together. At two positions, QTL for MFA, a physical trait related to wood stiffness, were clustered with QTL for lignin traits. Several cell wall candidate genes were co-located to QTL positions affecting different traits. Comparative QTL analysis with Eucalyptus globulus revealed two common QTL regions for cellulose and pulp yield. The QTL positions identified in this study provide a resource for identifying wood quality genes using the impending Eucalyptus genome sequence. Candidate genes identified in this study through co-location to QTL regions may be useful in association studies.     

UGPase和反义4CL基因对转基因烟草纤维素和木质素合成的调控

用根癌农杆菌介导法将源于紫穗槐的尿苷二磷酸葡萄糖焦磷酸化酶（UGPase）基因、反义4-香豆酸辅酶A连接酶（4CL）基因以及两者的双价基因分别转移至烟草中。PCR和Southern杂交检测证实外源基因已整合到转基因烟草基因组中。测定全纤维素和Klason木质素含量的结果显示,增强UGPase基因的表达可提高转基因植株的纤维素含量,但对木质素含量没有影响;抑制4CL基因的表达可显著降低转基因植株的木质素含量,但对纤维素含量没有影响;转移双价基因的转基因植株中纤维素含量增加而木质素含量降低。     

Degradation of polysaccharides and lignin in wood ozonation

Ozonation has been considered as a method for the pretreatment of plant biomass to obtain cellulose and monosaccharides. Ozone consumption by aspen wood with various moisture contents has been investigated. We have considered the gradual transformation of the substrate: wood to ozonated wood to cellulose-containing product (CP) to holocelluloze (HC) and to cellulose. Yields of ozonated wood (OW), the (CP), water-soluble ozonation products, HC, and cellulose have been determined. The lignin content in the CP has been estimated. Both HC and cellulose samples have been studied by IR spectroscopy. The degree of polymerization and molecular mass distribution of cellulose obtained from ozonated wood have been determined. It has been shown that wood destruction by ozone is accompanied by degradation of lignin, hemicelluloses, and cellulose.It has been found that physicochemical properties of cellulose obtained from ozonated wood can be regulated by the variation of the initial moisture content in the substrate. Both molecular ozone and radical species, which are generated in the course of ozone reactions with water present in the substrate structure, participate in wood destruction.     

Ectomycorrhizal Colonization and Diversity in Relation to Tree Biomass and Nutrition in a Plantation of Transgenic Poplars with Modified Lignin Biosynthesis

Wood from biomass plantations with fast growing tree species such as poplars can be used as an alternative feedstock for production of biofuels. To facilitate utilization of lignocellulose for saccharification, transgenic poplars with modified or reduced lignin contents may be useful. However, the potential impact of poplars modified in the lignification pathway on ectomycorrhizal (EM) fungi, which play important roles for plant nutrition, is not known. The goal of this study was to investigate EM colonization and community composition in relation to biomass and nutrient status in wildtype (WT, Populus tremula × Populus alba) and transgenic poplar lines with suppressed activities of cinnamyl alcohol dehydrogenase, caffeate/5-hydroxyferulate O-methyltransferase, and cinnamoyl-CoA reductase in a biomass plantation. In different one-year-old poplar lines EM colonization varied from 58% to 86%, but the EM community composition of WT and transgenic poplars were indistinguishable. After two years, the colonization rate of all lines was increased to about 100%, but separation of EM communities between distinct transgenic poplar genotypes was observed. The differentiation of the EM assemblages was similar to that found between different genotypes of commercial clones of Populus × euramericana. The transgenic poplars exhibited significant growth and nutrient element differences in wood, with generally higher nutrient accumulation in stems of genotypes with lower than in those with higher biomass. A general linear mixed model simulated biomass of one-year-old poplar stems with high accuracy (adjusted R² = 97%) by two factors: EM colonization and inverse wood N concentration. These results imply a link between N allocation and EM colonization, which may be crucial for wood production in the establishment phase of poplar biomass plantations. Our data further support that multiple poplar genotypes regardless whether generated by transgenic approaches or conventional breeding increase the variation in EM community composition in biomass plantations.     

Marker-Aided Selection of Polyploid Poplars

Polyploid breeding is an important means for creating elite varieties for the development of poplar plantations. However, polyploid poplars are rare in natural stands. In this study, we established an analytical toolkit to perform marker-aided selection of polyploid poplars. This toolkit contains 12 SSR primer pairs with sites located in the exonic DNA regions and resulting amplified microsatellites in the intronic/intergenic regions. Highly conserved primer pairs were selected by testing in eight species from four poplar sections. The amplified loci’s variability was examined using trees from a germplasm collection of Populus deltoides. Subsequently, copy numbers amplified by the highly variable primers were experimentally determined using progeny of a full-sib diploid pedigree. Based on the above tests, a subset of primers were finally selected and used for marker-aided selection of polyploid poplars from a set of natural Populus tomentosa stands. The reliability of the established analytical toolkit was further verified using a flow cytometer. We established a fast and reliable technique to screen polyploid poplars from natural stands.     

Genetic Improvement in <i>Juglans mandshurica</i> and Its Uses in China: Current Status and Future Prospects

Juglans mandshurica is an economically and ecologically valuable species that is used for various construction purposes, making luxurious furniture, as food and sources of medicinal substances and landscaping because of its excellent wood, edible fruits and rich in various types of chemical compounds. In the past few decades, several genetic improvements of J. mandshurica were made, with a focus on the selection of improved varieties and on breeding technology. Many elite provenances and families were selected based on growth traits or wood properties. In recent years, with the increasing demand for high-quality seedlings in Chinese forestry production, the breeding goals of genetic improvement for J. mandshurica were redefined to include other traits, such as fruit yield and contents of medicinal component. However, the improvement processes were still slow due to the long breeding cycle and the limited use of advanced breeding technologies, resulting in the selection of fewer improved varieties. In this review, we summarized the research progresses on genetic improvements of J. mandshurica and other related works, and discussed research gaps and suggested future directions for genetic improvement of the species. The review provides valuable insight for the selection of improved varieties and production of excellent germplasms.     

Sugarcane Internode Composition During Crop Development

Sugarcane sugar and bagasse can be utilized for the production of ethanol or other biofuels. A better understanding of the changes in composition with development along the stalk and with crop development will maximize the usage of sugarcane for this purpose. Two experiments were designed to elucidate internode composition changes during the growing season. In experiment 1, an internode of stalks of 5 modern cultivars were marked at the start of elongation, and then sampled every 1 to 2?weeks from July until October. Sugars were extracted and assayed, and a sequential detergent method was used to estimate hemicellulose, cellulose, and lignin contents. In experiment 2, internodes 1, 3, 5, 7, 9, and 11 down the stalk were sampled in late July (grand growth) and late September (ripening). Internode length, fresh weight, dry weight, water content, and sugar contents were determined as well as cell wall composition. Both experiments were repeated in 2?years. As internodes elongated, total sugar increased, and hemicellulose decreased as a proportion of neutral detergent fiber, while cellulose and lignin increased. After elongation, sucrose and lignin increased, and cellulose content decreased with internode age. The variability in cell wall composition among the five cultivars suggests that selection for desirable composition may be possible. In Experiment 2, hemicellulose contents were lower, and lignin and ash contents were higher at ripening than during grand growth. Delaying sugarcane harvest to maximize sucrose content may decrease bagasse suitability for cellulosic ethanol production because of the increased lignin content.