Selective Delignification of Aspen Wood Blocks In Vitro by Three White Rot Basidiomycetes

Aspen wood blocks were selectively delignified in the laboratory by Ischnoderma resinosum, Poria medulla-panis, and Xylobolus frustulatus. After 8 weeks only the outer surfaces of wood blocks were selectively delignified. The percentages of weight loss obtained after 4, 8, and 12 weeks showed that decay occurred at a relatively constant rate. Selectively delignified wood could be identified by using scanning electron microscopy only when lignin had been extensively removed from cell walls. X. frustulatus was able to form pockets of delignified wood throughout blocks after 12 weeks.     

Degradation of wood by the basidiomyceteCoriolopsis occidentalis

Chemical and microscopic features of wood decay by the basidiomyceteCoriolopsis occidentalis are described. The fungus was grown on blocks of poplar, oak, and fir wood and caused significant mass, lignin, and saccharide losses in all kinds of wood. Poplar wood was particularly strongly affected. Twelve weeks after inoculation dry mass, lignin, and saccharide contents were reduced by about 50%. The blocks became covered with mycelia and electron microscopy showed that secondary cell walls were degraded from the lumina and middle lamellae dissolved during later stages of incubation. The results indicate that the fungus belongs to simultaneous white-rotters.     

A rapid decrease in temperature induces latewood formation in artificially reactivated cambium of conifer stems

Background and Aims Latewood formation in conifers occurs during the later part of the growing season, when the cell division activity of the cambium declines. Changes in temperature might be important for wood formation in trees. Therefore, the effects of a rapid decrease in temperature on cellular morphology of tracheids were investigated in localized heating-induced cambial reactivation in Cryptomeria japonica trees and in Abies firma seedlings. Methods Electric heating tape and heating ribbon were wrapped on the stems of C. japonica trees and A. firma seedlings. Heating was discontinued when 11 or 12 and eight or nine radial files of differentiating and differentiated tracheids had been produced in C. japonica and A. firma stems, respectively. Tracheid diameter, cell wall thickness, percentage of cell wall area and percentage of lumen area were determined by image analysis of transverse sections and scanning electron microscopy. Key Results Localized heating induced earlier cambial reactivation and xylem differentiation in stems of C. japonica and A. firma as compared with non-heated stems. One week after cessation of heating, there were no obvious changes in the dimensions of the differentiating tracheids in the samples from adult C. japonica. In contrast, tracheids with a smaller diameter were observed in A. firma seedlings after 1 week of cessation of heating. Two or three weeks after cessation of heating, tracheids with reduced diameters and thickened cell walls were found. The results showed that the rapid decrease in temperature produced slender tracheids with obvious thickening of cell walls that resembled latewood cells. Conclusions The results suggest that a localized decrease in temperature of stems induces changes in the diameter and cell wall thickness of differentiating tracheids, indicating that cambium and its derivatives can respond directly to changes in temperature.     

Comparative Studies of Delignification Caused by Ganoderma Species

Isolates of six species of Ganoderma in the G. lucidum complex were evaluated for their ability to decay wood of Quercus hypoleucoides A. Camus and Abies concolor (Gord. and Glend.) Lindl. ex. Hildebr. by using in vitro agar block decay tests. Morphological, ultrastructural, and chemical studies of decayed wood were used to determine the extent of delignification or simultaneous decay caused by each species of Ganoderma. All species decayed both white fir and oak wood; however, less percent weight loss (%WL) occurred in white fir than oak. In white fir, isolates of two undescribed Ganoderma species (RLG16161, RLG16162, JEA615, and JEA625) caused significantly higher%WL (21 to 26%) than that in G. colossum, G. oregonense, G. meredithiae, and G. zonatum (10 to 16%). Only Ganoderma sp. isolates JEA615 and JEA625 caused delignification, with JEA615 causing a lignin-to-glucose gram loss ratio of 1.6:1. Morphological and ultrastructural studies confirmed delignification by this fungus and showed that some delignification had occurred by all of the species, although areas of delignification were limited to small regions adjacent to simultaneously decayed cells. In oak, G. colossum caused significantly less%WL (22 to 35%) than the other species (38 to 52%). All of the species, except G. meredithiae, caused delignification with lignin-to-glucose gram loss ratios ranging from 1.4 to 4.9:1. Extensive delignification by isolates of G. colossum and G. oregonense was observed; moderate delignification was caused by the other species. Ganoderma meredithiae caused a simultaneous decay, with only small localized regions of cells delignified, while delignification by G. zonatum was irregular, with specific zones within the cell wall delignified. The thermophilic and chlamydosporic G. colossum has the capacity to cause extensive delignification and appears ideally suited for use in lignin degradation studies and biotechnological applications of lignin-degrading fungi.     

Degradation of wood and enzyme production by Ceriporiopsis subvermispora

The degradation of the components of Japanese beech and Japanese cedar wood was measured over time in cultures of the white-rot fungus Ceriporiopsis subvermispora. Although there was no initial degradation of cedar wood, after 12 weeks the mass loss of both cedar and beech wood was 15–20%. The mass losses of filter paper in beech wood-containing cultures and glucose cultures after 12 weeks were 87% and 70%, respectively. The ratio of lignin loss to mass loss of both beech and cedar wood cultures approached 2.0. Although the cellulose loss in cedar wood was very low throughout the 12-week incubation, C. subvermispora degraded the hemicellulose in Japanese cedar much more effectively than that in Japanese beech. These results confirm that C. subvermispora is a selective lignin degrader. During the 12-week incubation with Japanese beech wood, C. subvermispora continuously produced at least one of three phenol oxidases: laccase was produced initially, followed by Mn-independent peroxidase activity peaking at 6 weeks and Mn-dependent peroxidase activity peaking at 10 weeks. Lignin peroxidase and carboxymethylcellulase activities peaked after 3 weeks of incubation. Avicelase activity was present throughout the incubation period, although the activity was very low. The low-molecular-mass fraction of the extracellular medium, which catalyzes a redox reaction between O₂ and electron donors to produce hydroxyl radical, may act synergistically with the enzymes to degrade wood cell walls.     

Characterization of Palo Podrido, a Natural Process of Delignification in Wood

Chemical and morphological changes of incipient to advanced stages of palo podrido, an extensively delignified wood, and other types of white rot decay found in the temperate forests of southern Chile were investigated. Palo podrido is a general term for white rot decay that is either selective or nonselective for the removal of lignin, whereas palo blanco describes the white decayed wood that has advanced stages of delignification. Selective delignification occurs mainly in trunks of Eucryphia cordifolia and Nothofagus dombeyi, which have the lowest lignin content and whose lignins have the largest amount of β-aryl ether bonds and the highest syringyl/guaiacyl ratio of all the native woods included in this study. A Ganoderma species was the main white rot fungus associated with the decay. The structural changes in lignin during the white rot degradation were examined by thioacidolysis, which revealed that the β-aryl ether-linked syringyl units were more specifically degraded than the guaiacyl ones, particularly in the case of selective delignification. Ultrastructural studies showed that the delignification process was diffuse throughout the cell wall. Lignin was first removed from the secondary wall nearest the lumen and then throughout the secondary wall toward the middle lamella. The middle lamella and cell corners were the last areas to be degraded. Black manganese deposits were found in some, but not all, selectively delignified samples. In advanced stages of delignification, almost pure cellulose could be found, although with a reduced degree of polymerization. Cellulolytic enzymes appeared to be responsible for depolymerization. A high brightness and an easy refining capacity were found in an unbleached pulp made from selectively delignified N. dombeyi wood. Its low viscosity, however, resulted in poor resistance properties of the pulp. The last stage of degradation (i.e., decomposition of cellulose-rich secondary wall layers) resulted in a gelatinlike substance. Ultrastructural and chemical analyses of this substance showed the matrix to have no microfibrillar structure characteristic of woody cell walls but to still be rich in glucan.     

Comparative study on the delignification of Azadirachta indica (L) Del., wood by Chrysosporium asperatum and Trichoderma harzianum

Structural alterations induced in response to degradation by two white rot Basidiomycetes on the secondary xylem of Azadirachta indica (L) Del., was compared. In vitro decay test was employed to investigate the pattern of delignification of Azadirachta wood by Trichoderma harzianum and Chrysosporium asperatum. Wood samples inoculated with both the strains were analyzed for different periods viz. 30, 60, 90 and 120 days after fungal inoculation. Initially there was no appreciable percent weight loss of the wood blocks but later on (after 60 days) it increased rapidly and was found similar for both the strains (43-46% of wood mass). Samples inoculated with both the strains showed dual pattern of degradation i.e. selective delignification in the initial stage followed by simultaneous rot during advance stage of decay. Separation of the cells due to dissolution of middle lamella was the characteristic feature of both strains but in the advanced stage of decay, formation of erosion troughs were conspicuous in all the cell types. Other features such as cell wall thinning, rounded pit erosion, formation of erosion channels and bore holes were also observed frequently. Initially, fungal invasion started through the vessel lumen, followed by all the cell types of the xylem. From the vessels, mycelia entered into the adjacent rays and parenchyma cells through the pits. In advanced stage, degradation was so pronounced that rays were partially or even completely destroyed while many cells including vessels were either deformed or destroyed due to loss of rigidity of their walls. Structural alterations induced in response to C. asperatum and T. harzianum attack is described in details.     

Photoperiodic Control of Natural Growth Substances and Wood Formation in Larch (Larix decidua D.C.)

One-year-old larch plants were submitted to one of the followingphotoperiodic treatments in greenhouses: C.L.(H) = Continuous light, which included 16 hours high-intensityillumination/24-hour cycle. C.L.(L) = Continuous light, which included 12 hours low-intensityillumination/24-hour cycle. S.D. = Short day. The investigation of the wood anatomy and the content of growth-promotingand growth-inhibiting substances in different parts of the plantsat different times of plant collection showed remarkable correlationbetween the formation of thick-walled tracheids in S.D.- andC.L.(L)-treated plants and the accumulation of water-solubleinhibitors in the cortical tissues. Plants under C.L.(H) conditionsdid not produce thick-walled tracheids and no significant accumulationof inhibitors was observed. The photoperiodically controlledchanges in the content of promoters could not be correlatedwith the thickening of cell walls of tracheids. These changeswere, however, correlated with the extension-growth of the shoot. The results are discussed in relation to the possible influenceof these two groups of growth substances on the thickening ofcell walls and on the increase in the radial diameter of cellsdifferentiating into the conducting elements of wood in thecambial zone.     

Oxalic acid overproduction by copper-tolerant brown-rot basidiomycetes on southern yellow pine treated with copper-based preservatives

Accumulation of oxalic acid (OA) by brown-rot fungi and precipitation of copper oxalate crystals in wood decayed by copper-tolerant decay fungi has implicated OA in the mechanism of copper tolerance. Understanding the role of OA in copper tolerance is important due to an increasing reliance on copper-based wood preservatives. In this study, four copper-tolerant brown-rot fungi were evaluated for decay capacity and OA production in early stages of exposure to four waterborne copper-based wood preservatives (ammonical copper quat type B and D, ammonical copper citrate, and chromated copper arsenate, type C) and one oilborne copper-based wood preservative (oxine copper) in southern yellow pine blocks. Weight losses were less than 14% during the 4-week incubation. The presence of copper in waterborne preservatives uniformly stimulated OA production by the test fungi within 2 weeks of exposure of the treated blocks to test fungi; 66% to 93% more OA was produced in treated blocks than untreated controls. Oxine copper, a nickel-containing oilborne preservative, prevented both weight loss and OA production in all fungi tested.     

Localization of cell wall polysaccharides in normal and compression wood of radiata pine: relationships with lignification and microfibril orientation

The distribution of noncellulosic polysaccharides in cell walls of tracheids and xylem parenchyma cells in normal and compression wood of Pinus radiata, was examined to determine the relationships with lignification and cellulose microfibril orientation. Using fluorescence microscopy combined with immunocytochemistry, monoclonal antibodies were used to detect xyloglucan (LM15), β(1,4)-galactan (LM5), heteroxylan (LM10 and LM11), and galactoglucomannan (LM21 and LM22). Lignin and crystalline cellulose were localized on the same sections used for immunocytochemistry by autofluorescence and polarized light microscopy, respectively. Changes in the distribution of noncellulosic polysaccharides between normal and compression wood were associated with changes in lignin distribution. Increased lignification of compression wood secondary walls was associated with novel deposition of β(1,4)-galactan and with reduced amounts of xylan and mannan in the outer S2 (S2L) region of tracheids. Xylan and mannan were detected in all lignified xylem cell types (tracheids, ray tracheids, and thick-walled ray parenchyma) but were not detected in unlignified cell types (thin-walled ray parenchyma and resin canal parenchyma). Mannan was absent from the highly lignified compound middle lamella, but xylan occurred throughout the cell walls of tracheids. Using colocalization measurements, we confirmed that polysaccharides containing galactose, mannose, and xylose have consistent correlations with lignification. Low or unsubstituted xylans were localized in cell wall layers characterized by transverse cellulose microfibril orientation in both normal and compression wood tracheids. Our results support the theory that the assembly of wood cell walls, including lignification and microfibril orientation, may be mediated by changes in the amount and distribution of noncellulosic polysaccharides.     

Selective diminishment of virus-specific translatable mRNA in the densonucleosis virus-infected midgut of the silkworm, Bombyx mori, reared at a supraoptimal temperature

Effect of a supraoptimal temperature on the accumulation of virus-specific translatable mRNAs was examined in the larvae of the silkworm. Bombyx mori, infected with Bombyx densonucleosis virus type 2. The results showed that incubation of infected larvae at 35 degrees C resulted in a rapid and selective decrease in the virus-specific translatable mRNAs which preexisted in the infected midgut. Upon temperature-shift from 35 degrees to 25 degrees C, the virus-specific translatable mRNAs became clearly observed within 12 hr. These results indicate that a supraoptimal temperature restricts the accumulation of virus-specific translatable mRNAs. Both rapid decay and suppressed synthesis might be responsible for the selective restriction of virus-specific translatable mRNA accumulation at a supraoptimal temperature.     

Bioresistance of poplar wood compressed by combined hydro-thermo-mechanical wood modification (CHTM): Soft rot and brown-rot

This work studied fungal bioresistance of combined hydro-thermo-mechanically modified (CHTM) poplar wood. The CHTM technique, introduced by Mohebby et al. (2009), is a combination of two wood modification techniques-hydrothermal wood modification and densification of wood. Blocks of poplar wood were initially treated hydrothermally at temperatures of 120, 150, and 180 °C for holding times of 0, 30, and 90 min. Afterwards, the treated blocks were compressed by a hot press (160 and 180 °C) for 20 min with a compression set of 60%. After the CHTM-treated blocks were dried, small specimens were cut for soft-rot and brown-rot decay tests according to ENV 807 and EN 113. Mass losses as well as metabolic moisture contents were determined in the decayed samples. Results revealed that the combination of wood modification techniques showed fungal suppression. It was also found that the hydrothermal treatment step could significantly reduce fungal attack in comparison with densification. Reduction of the mass losses was associated with the hydrothermal treatment temperature. Also, the level of metabolic moisture content was correlated with the mass losses for both fungi. Any reduction of the mass loss decreased the moisture content in the wood.     

Delignification kinetics of corn stover in lime pretreatment

Corn stover was pretreated with excess calcium hydroxide (0.5 g Ca(OH)(2)/g raw biomass) in non-oxidative and oxidative conditions at 25, 35, 45, and 55 degrees C. The delignification kinetic model of corn stover used three first-order reactions with following forms: W(L) = 0.09 x exp(-infinity x t) + 0.28 x exp(-k(2) x t) + 0.63 x exp(-k(3) x t) in non-oxidative pretreatment; W(L) = 0.16 x exp(-infinity x t) + 0.27 x exp(-k(2) x t) + 0.57 x exp(-k(3) x t) in oxidative pretreatment. The first term corresponds to the initial phase, which is essentially infinite at the time scale of the reaction (weeks). The second and third terms correspond to the bulk and residual phases of delignification. The activation energies for delignification in the oxidative lime pretreatment reactions were estimated as 50.15 and 54.21 kJ/mol in the bulk and residual phases, respectively, which are similar to the Kraft delignification of bagasse, but much less than in Kraft delignification of wood.     

Induction of secondary dormancy in Amaranthus caudatus seeds

Nondormant A. caudatus seeds germinated in the darkat temperatures between 20 and 35° but not at 45 °C.Incubation at this temperature for at least 10 h inhibited seedgermination over the temperature range 20 to 35 °C,temperatures previously suitable for germination. Thus incubation at 45°C induced secondary dormancy. Mechanical or chemicalscarification or exposure to pure oxygen caused complete or almost completegermination of dormant seeds although more slowly in comparison to nondormantseeds. Secondary dormant scarified seeds required a lower concentration of ABAthan nondormant seeds to inhibit germination. The high temperature, whichinduced dormancy, 45 °C, caused the seed coat to be partiallyresponsible for secondary dormancy. Involvement of ABA (synthesis orsensitivity) in the induction and/or maintenance of this dormancy should beconsidered.     

Effect of temperature shock and elevated incubation temperature on androgenic embryo yield of diploid potato

Using three diploid tuber-bearing Solanum clones as anther donors, experiments were conducted on the effect of high temperature shock and elevated incubation temperature during anther culture on androgenic embryo production. Five incubation treatments were tested on two clones and three treatments were repeated in a second experiment on one of the same clones and an additional one. In the first experiment, temperature treatment, genotype, date of culture initiation, and their interactions were all significant sources of variation. A treatment combining a high temperature shock (35 °C for 12 h) with elevated incubation temperature (30/20 °C) yielded 11 times as many embryos (44 per flask) as the control 20 °C (4 per flask). By conducting several replications per day of bud collection, the significant variation due to experimental dates was separated from experimental error to provide a more sensitive test of treatment effects. Temperature shock (35 °C 12h) during anther culture did not appear to influence the subsequent conversion rate of androgenic embryos.     

Diffuse competition for heterogeneous substrate in soil among six species of wood-decomposing basidiomycetes

Competition among six wood decay fungi was studied using 15×15 mm wood blocks placed in 250×250 mm plastic trays filled with unsterilized sand or clay. The wood blocks were preinoculated with Heterobasidion annosum (Fr.) Bref., Resinicium bicolor (Alb. & Schw. ex Fr.) Parm., Phanerochaete sanguinea (Fr.) Hjortstam, Coniophora sp. DC. ex Me"rat, Armillaria borealis Marxmuller and Korhonen and Hypholoma capnoides (Fr.) Kummer before they were combined in all possible combinations in the trays. Two methods were used, one with all wood blocks inoculated, and one with sterilized non-inoculated wood blocks distributed between the inoculated ones. Wood blocks preinoculated with the six species were also used in a pairwise competition test. Following incubation for 9 months in darkness at 21°C, mycelia were reisolated and identified. R. bicolor was most successful at invading through the soil and replacing other species in the wood blocks. P. sanguinea, Coniophora sp. and H. capnoides also had some success.     

Tetracentron Wood from the Miocene of Noto Peninsula,Central Japan,with a short revision of homoxylic fossil woods

A vesselless fossil wood was discovered in the Miocene Yanagida Formation in the Noto Peninsula, central Japan. This fossil has distinct growth rings with gradual transition from the early- to the latewood ; tracheids, which are called 'usual traeheids' here, constitute the ground mass of the wood and have typical scalariform bordered pits on radial walls in the earlywood and circular sparse pits on those in the latewood ; rays are 1\2-4 cells wide and heterogeneous with low to high uniseriate wings; axial parenchyma strands are scattered in the latewood. This wood has a peculiar feature; sporadic radial files of broad tracheids whose tangential walls have crowded alternate bordered pits. The radial walls have crowded half-bordered pits to ray cells, but no pits to the usual tracheids. Among all of the extant and extinct angiosperms and gymnosperms, these unusual tracheids occur only in Tetracentron. From these features, we refer the fossil to the extant genus Tetracentron, and name it T. japonoxylum. A revision of homoxylic woods is made for comparision with the present fossil. Tetracentron japonoxylum is the only fossil wood of Tetracentron.     

Bacterial degradation of lignified wood cell walls in anaerobic aquatic habitats

Test blocks of beech (Fagus sylvatica) and Scots pine (Pinus sylvestris) were buried in fresh, brackish, and seawater anaerobic muds for periods ranging between 1 and 18 months. At appropriate time intervals the test blocks were recovered and examined for changes in weight and for bacterial attack of lignified wood cell walls. Only small weight losses occurred. Scanning electron microscopy studies revealed that there was extensive superficial bacterial erosion of beech wood cell walls. The decay patterns are illustrated by micrographs and discussed in relation to other types of bacterial attack.     

Evaluation of a combined brown rot decay–chemical delignification process as a pretreatment for bioethanol production from Pinus radiata wood chips

Wood chips of Pinus radiata softwood were biotreated with the brown rot fungus (BRF) Gloeophyllum trabeum for periods from 4 and 12 weeks. Biodegradation by BRF leads to an increase in cellulose depolymerization with increasing incubation time. As a result, the intrinsic viscosity of holocellulose decreased from 1,487 cm³/g in control samples to 783 and 600 cm³/g in 4- and 12-week decayed wood chips, respectively. Wood weight and glucan losses varied from 6 to 14% and 9 to 21%, respectively. Undecayed and 4-week decayed wood chips were delignified by alkaline (NaOH solution) or organosolv (ethanol/water) processes to produced cellulosic pulps. For both process, pulp yield was 5–10% lower for decayed samples than for control pulps. However, organosolv bio-pulps presented low residual lignin amount and high glucan retention. Chemical pulps and milled wood from undecayed and 4-week decayed wood chips were pre-saccharified with cellulases for 24 h at 50°C followed by simultaneous saccharification and fermentation (SSF) with the yeast Saccharomyces cerevisiae IR2-9a at 40°C for 96 h for bioethanol production. Considering glucan losses during wood decay and conversion yields from chemical pulping and SSF processes, no gains in ethanol production were obtained from the combination of BRF with alkaline delignification; however, the combination of BRF and organosolv processes resulted in a calculated production of 210 mL ethanol/kg wood or 72% of the maximum theoretically possible from that pretreatment, which was the best result obtained in the present study.     

Bacterial degradation of lignified wood cell walls in anaerobic aquatic habitats.

Test blocks of beech (Fagus sylvatica) and Scots pine (Pinus sylvestris) were buried in fresh, brackish, and seawater anaerobic muds for periods ranging between 1 and 18 months. At appropriate time intervals the test blocks were recovered and examined for changes in weight and for bacterial attack of lignified wood cell walls. Only small weight losses occurred. Scanning electron microscopy studies revealed that there was extensive superficial bacterial erosion of beech wood cell walls. The decay patterns are illustrated by micrographs and discussed in relation to other types of bacterial attack.