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When various lignin-related para-phenolic benzoic acids, para-phenolic cinnamic acids, para-phenolic phenylpropionic acids, the corresponding unsubstituted and 4-O-methylated derivatives, and 4-hydroxyl substituted benzaldehydes were tested on the growth of eight white-rot fungi, methylation of the 4-hydroxy substituent resulted, in most cases, in increased inhibition of fungal growth. This effect was most notable with monomethoxylated compounds. When the aromatic ring contained additional methoxyl substituents, the toxicity of the 4-O-methylated derivative was less pronounced. Marked inhibition of fungal growth was also observed with aromatic compounds lacking a para-substituent. Higher concentrations of aromatic aldehydes were manifestly more toxic than the corresponding carboxylic acid.J.A. Buswell is with the Department of Biology, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong. K.-E.L. Eriksson is with the Department of Biochemistry, The University of Georgia, Athens, Georgia, 30602, USA.  相似文献   
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Background Lignin is a polyphenolic polymer that strengthens and waterproofs the cell wall of specialized plant cell types. Lignification is part of the normal differentiation programme and functioning of specific cell types, but can also be triggered as a response to various biotic and abiotic stresses in cells that would not otherwise be lignifying.Scope Cell wall lignification exhibits specific characteristics depending on the cell type being considered. These characteristics include the timing of lignification during cell differentiation, the palette of associated enzymes and substrates, the sub-cellular deposition sites, the monomeric composition and the cellular autonomy for lignin monomer production. This review provides an overview of the current understanding of lignin biosynthesis and polymerization at the cell biology level.Conclusions The lignification process ranges from full autonomy to complete co-operation depending on the cell type. The different roles of lignin for the function of each specific plant cell type are clearly illustrated by the multiple phenotypic defects exhibited by knock-out mutants in lignin synthesis, which may explain why no general mechanism for lignification has yet been defined. The range of phenotypic effects observed include altered xylem sap transport, loss of mechanical support, reduced seed protection and dispersion, and/or increased pest and disease susceptibility.  相似文献   
4.
木质素降解酶及相关基因研究进展   总被引:2,自引:0,他引:2  
生物质的高效综合利用已成为全球关注的热点问题。生物质的主要成分是木质素、纤维素和半纤维素,其利用的关键是如何去除木质素,从而提高纤维素和半纤维素的得率。其中利用真菌的生物预处理方法因条件温和、无二次污染等优点符合全球经济可持续发展需要,受到研究者的普遍关注。综述了近年国内外真菌分泌的主要木质素降解酶,包括木质素过氧化物酶(Li P)、锰过氧化物酶(Mn P)、漆酶(laccase)和多功能过氧化物酶(VP)的主要特点,总结了木质素降解相关酶的基因工程、基因组学的研究成果,并对其发展前景进行了展望。  相似文献   
5.
Following our previous findings of high extracellular redox activity in lichens, the results of the work presented here identify the enzymes involved as laccases. Despite numerous data on laccases in fungi and flowering plants, this is the first report of the occurrence of laccases in lichenized ascomycetes. Extracellular laccase activity was measured in 40 species of lichens from different taxonomic groupings and contrasting habitats. Out of 20 species tested from suborder Peltigerineae, 18 displayed laccase activity, while activity was absent in species tested from other lichen groups. Identification of the enzymes as laccases was confirmed by the ability of lichen leachates to readily metabolize substrates such as 2,2′-azino(bis-3-ethylbenzthiazoline-6-sulfonate) (ABTS), syringaldazine and o-tolidine in the absence of hydrogen peroxide, sensitivity of the enzymes to cyanide and azide, the enzymes having typical laccase pH and temperature optima, and an absorption spectrum with a peak at 614 nm. Desiccation and wounding stimulated laccase activity. Laccase activity was not increased after treatment with normal inducers of laccase synthesis, suggesting that they are constitutively expressed. Electrophoresis showed that the active form of laccase from Peltigera malacea was a tetramer with an unusually high molecular mass of 340 kDa and an isoelectric point (pI) of 4.7. The finding of abundant extracellular redox enzymes known to actively produce reactive oxygen species suggest that their roles may include increasing nutrient supply to lichens by delignification, and deterring pathogens by contributing to the oxidative burst. Furthermore, once released into the environment, they may participate in the carbon cycle by facilitating the breakdown or formation of humic substances.  相似文献   
6.
Wood decay under the microscope   总被引:3,自引:0,他引:3  
Many aspects of the interactions between host wood structure and fungal activity can be revealed by high resolution light microscopy, and this technique has provided much of the information discussed here. A wide range of different types of decay can result from permutations of host species, fungal species and conditions within wood. Within this spectrum, three main types are commonly recognised: brown rot, white rot and soft rot. The present review explores parts of the range of variation that each of these encompasses and emphasizes that degradation modes appear to reflect a co-evolutionary adaptation of decay fungi to different wood species or the lignin composition within more primitive and advanced wood cell types. One objective of this review is to provide evidence that the terms brown rot, white rot and soft rot may not be obsolete, but rigid definitions for fungi that are placed into these categories may be less appropriate than thought previously. Detailed knowledge of decomposition processes does not only aid prognosis of decay development in living trees for hazard assessment but also allows the identification of wood decay fungi that can be used for biotechnology processes in the wood industry. In contrast to bacteria or commercial enzymes, hyphae can completely ramify through solid wood. In this review evidence is provided that wood decay fungi can effectively induce permeability changes in gymnospermous heartwood or can be applied to facilitate the identification of tree rings in diffuse porous wood of angiosperms. The specificity of their enzymes and the mild conditions under which degradation proceeds is partly detrimental for trees, but also make wood decay fungi potentially efficient biotechnological tools.  相似文献   
7.
We studied the effect of long-term nitrogen fertilisation on wood chemistry at two boreal sites in Finland: the northern site (Kemijärvi) and the southern site (Heinola). N-fertilisation was repeated in five-year intervals from the 1960s. Norway spruce (Picea abies L. Karst.) trees that had been planted in 1938 and 1954, in the northern and the southern site, respectively, were harvested in October 2002. Altogether 20 trees, in five different size classes, either unfertilised or fertilised, were felled. Wood sections at breast height, consisting of five consecutive annual rings, from six (Kemijärvi) or five (Heinola) points with different distances from the pith were examined. Differences in growth between the northern and southern sites were marked in favour of the southern site. In the northern site fertilisation had clearly increased the diameter growth, while in the southern site fertilisation had no effect. Nitrogen fertilisation resulted in slight changes in wood chemistry that included increased nitrogen concentrations in the northern site and extractives in the southern site. Stem wood had higher concentrations of extractives, starch, and uronic acids, and lower concentration of cellulose, in the northern than in the southern site. Changes in the stem wood chemistry along radial axis were marked. The changes in wood chemistry are discussed in relation to the physiological function and also how the changes can influence the suitability of wood for different end-use purposes.  相似文献   
8.
Endophytic fungi occur on various types of leaf litter, but few studies have been done on their roles as saprophytes in decomposition. This study examined the succession of fungi in live, newly shed, and decomposing leaves at 2 months of decomposition of Camellia japonica and chemical changes in decomposing leaves colonized by endophytes. Coccomyces nipponicum, Lophodermium sp., Geniculosporium sp. 1, and Colletotrichum gloeosporioides were isolated from living leaves. Coccomyces nipponicum and Lophodermium sp. were also isolated frequently from newly shed and decomposing leaves. These two fungi caused a decrease of lignin content and bleaching in decomposing leaves under field and laboratory conditions. Total hyphal length in decomposing leaves was higher in bleached portions than in surrounding nonbleached portions, which probably reflected the early onset of hyphal growth of endophytes inside leaf tissue at leaf senescence or death. Incubation of newly shed leaves that were sterilized to exclude previously established endophytes resulted in no occurrence of bleached portions in decomposing leaves on the forest floor. This result indicated that these endophytes were incapable of colonizing leaves directly after litterfall and that the persistence of endophytes from live leaves was crucial for their colonization in decomposing leaves.  相似文献   
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10.
Rice straw was pretreated using aqueous-ammonia solution at moderate temperatures to enable production of the maximum amount of fermentable sugars from enzymatic hydrolysis. The effects of various operating variables including pretreatment temperature, pretreatment time, the concentration of ammonia and the solid-to-liquid ratio on the degree of lignin removal and the enzymatic digestibility were optimized using response surface methodology. The optimal reaction conditions, which resulted in an enzymatic digestibility of 71.1%, were found to be 69 °C, 10 h and an ammonia concentration of 21% (w/w). The effects of different commercial cellulases and the additional effect of a non-cellulolytic enzyme, xylanase, were also evaluated. Additionally, simultaneous saccharification and fermentation was conducted with rice straw to assess the ethanol production yield and productivity.  相似文献   
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