Laccases of fungi attract considerable attention due to their possible involvement in the transformation of a wide variety of phenolic compounds including the polymeric lignin and humic substances. So far, more than a 100 enzymes have been purified from fungal cultures and characterized in terms of their biochemical and catalytic properties. Most ligninolytic fungal species produce constitutively at least one laccase isoenzyme and laccases are also dominant among ligninolytic enzymes in the soil environment. The fact that they only require molecular oxygen for catalysis makes them suitable for biotechnological applications for the transformation or immobilization of xenobiotic compounds.

Fungal laccases - occurrence and properties.

INTRODUCTION. Internal Organization of the Plant Body. Summary of Types of Cells and Tissues. General References. DEVELOPMENT OF THE SEED PLANT. The Embryo. From embryo to the Adult Plant. Apical Meristems and Their Derivatives. Differentiation, Specialization, and Morphogenesis. References. THE CELL. Cytoplasm. Nucleus. Plastids. Mitochondria. Microbodies. Vacuoles. Paramural Bodies. Ribosomes. Dictyosomes. Endoplasmic Reticulum. Lipid Globules. Microtubules. Ergastic Substances. References. CELL WALL. Macromolecular Components and Their Organization in the Wall. Cell Wall Layers. Intercellular Spaces. Pits, Primary Pit--Fields, and Plasmodesmata. Origin of Cell Wall During Cell Division. Growth of Cell Wall. References. PARENCHYMA AND COLLENCHYMA. Parenchyma. Collenchyma. References. SCLERENCHYMA. Sclereids. Fibers. Development of Sclereids and Fibers. References. EPIDERMIS. Composition. Developmental Aspects. Cell Wall. Stomata. Trichomes. References. XYLEM: GENERAL STRUCTURE AND CELL TYPES. Gross Structure of Secondary Xylem. Cell Types in the Secondary Xylem. Primary Xylem. Differentiation of Tracheary Elements. References. XYLEM: VARIATION IN WOOD STRUCTURE. Conifer Wood. Dicotyledon Wood. Some Factors in Development of Secondary Xylem. Identification of Wood. References. VASCULAR CAMBIUM. Organization of Cambium. Developmental Changes in the Initial Layer. Patterns and Causal Relations in Cambial Activity. References. PHLOEM. Cell Types. Primary Phloem. Secondary Phloem. References. PERIDERM. Structure of Periderm and Related Tissues. Development of Periderm. Outer Aspect of Bark in Relation to Structure. Lenticels. References. SECRETORY STRUCTURES. External Secretory Structures. Internal Secretory Structures. References. THE ROOT: PRIMARY STATE OF GROWTH. Types of Roots. Primary Structure. Development. References. THE ROOT: SECONDARY STATE OF GROWTH AND ADVENTITIOUS ROOTS. Common Types of Secondary Growth. Variations in Secondary Growths. Physiologic Aspects of Secondary Growth in Roots. Adventitious Roots. References. THE STEM: PRIMARY STATE OF GROWTH. External Morphology. Primary Structure. Development. References. THE STEM: SECONDARY GROWTH AND STRUCTURAL TYPES. Secondary Growth. Types of Stems. References. THE LEAF: BASIC STRUCTURE AND DEVELOPMENT. Morphology. Histology of Angiosperm Leaf. Development. Abscission. References. THE LEAF: VARIATIONS IN STRUCTURE. Leaf Structure and Environment. Dicotyledon Leaves. Monocotyledon Leaves. Gymnosperm Leaves. References. THE FLOWER: STRUCTURE AND DEVELOPMENT. Concept. Structure. Development. References. THE FLOWER: REPRODUCTIVE CYCLE. Microsporogenesis. Pollen. Male Gametophyte. Megasporogenesis. Female Gametophyte. Fertilization. References. THE FRUIT. Concept and Classification. The Fruit Wall. Fruit Types. Fruit Growths. Fruit Abscission. References. THE SEED. Concept and Morphology. Seed Development. Seed Coat. Nutrient Storage Tissues. References. EMBRYO AND SEEDLING. Mature Embryo. Development of Embryo. Classification of Embryos. Seedling. References. Glossary. Index.

Anatomy of Seed Plants

Wood is the main renewable material on Earth and is largely used as building material and in paper-pulp manufacturing. This review describes the composition of lignocellulosic materials, the different processes by which fungi are able to alter wood, including decay patterns caused by white, brown, and soft-rot fungi, and fungal staining of wood. The chemical, enzymatic, and molecular aspects of the fungal attack of lignin, which represents the key step in wood decay, are also discussed. Modern analytical techniques to investigate fungal degradation and modification of the lignin polymer are reviewed, as are the different oxidative enzymes (oxidoreductases) involved in lignin degradation. These include laccases, high redox potential ligninolytic peroxidases (lignin peroxidase, manganese peroxidase, and versatile peroxidase), and oxidases. Special emphasis is given to the reactions catalyzed, their synergistic action on lignin, and the structural bases for their unique catalytic properties. Broadening our knowledge of lignocellulose biodegradation processes should contribute to better control of wood-decaying fungi, as well as to the development of new biocatalysts of industrial interest based on these organisms and their enzymes. [Int Microbiol 2005; 8(3):195-204]

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Biodegradation of lignocellulosics: microbial, chemical, and enzymatic aspects of the fungal attack of lignin.

FTIR studies of the changes in wood chemistry following decay by brown-rot and white-rot fungi

Severe droughts have caused widespread tree mortality across many forest biomes with profound effects on the function of ecosystems and carbon balance. Climate change is expected to intensify regional-scale droughts, focusing attention on the physiological basis of drought-induced tree mortality. Recent work has shown that catastrophic failure of the plant hydraulic system is a principal mechanism involved in extensive crown death and tree mortality during drought, but the multi-dimensional response of trees to desiccation is complex. Here we focus on the current understanding of tree hydraulic performance under drought, the identification of physiological thresholds that precipitate mortality and the mechanisms of recovery after drought. Building on this, we discuss the potential application of hydraulic thresholds to process-based models that predict mortality.

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Triggers of tree mortality under drought

Effects of gamma irradiation on morphological changes and biological responses in plants

SUMMARY Wood in wet environments is attacked and degraded by soft rot fungi and erosion and tunnelling bacteria, which are more tolerant to high moisture and reduced oxygen conditions than basidiomycetes, such as white and brown rot fungi. Since wood decaying basidiomycete fungi are normally more aggressive and can degrade wood faster than soft rot fungi and bacteria, wood in wet environments can survive for a relatively long time. Archaeological investigations show that wood buried deep in ocean sediments can survive for hundreds and even thousands of years. In this review degradation patterns of various types of microbial wood decay are briefly described, and examples of decay type(s) in wood exposed in various wet environments presented. It is important to understand biological wood decay in wet environments in order to find appropriate ways to prolong woodʼs service life and properly restore wooden artefacts.

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Micromorphological characteristics of wood biodegradation in wet environments: a review

Rice husk is a by-product of rice milling process, and a great resource as a raw biomass material for manufacturing value-added composite products. One of the potential applications is to use rice husk as filler for manufacturing lignocellulosic fiber–thermoplastic composites. This study was conducted to examine the silica distribution in rice husk in preparation to use it as reinforcing filler for thermoplastic polymers. Microscopic techniques, such as light microscopy, scanning electron microscopy and field-emission SEM (FE-SEM) were used to observe the surface and internal structure of rice husk. Microscopic examination showed that two main components of husk, lemma and palea consisted of outer epidermis, layers of fibers, vascular bundles, parenchyma cells, and inner epidermis, in sequence from the outer to the inner surface. Histochemical staining showed that epidermal and fiber cell walls were lignified, and the walls of parenchyma and lower epidermal cells were not lignified. The outer epidermal walls were extremely thick, highly convoluted and lignified. The outer surface of both lemma and palea were conspicuously ridged. The energy dispersive X-ray micro-analysis attached to the FE-SEM provided information on the distribution of silica in the husk. Most of the silica was present in the outer epidermal cells, being particularly concentrated in the dome-shaped protrusions. These observations provided valuable background information on the organization of husk tissues and the distribution of silica, which will help optimize processes related to the use of rice husk for making lignocellulosic fiber–thermoplastic composites in our future work.

Characterization of anatomical features and silica distribution in rice husk using microscopic and micro-analytical techniques

Microscopic examination showed the cell wall decay pattern produced by the brown-rot fungus Coniophora puteana to be different from the degradation pattern known to be typical for brown-rot fungi. Erosion and thinning of cell walls in patterns considered to be characteristic of white-rot decay were observed. In particular, the fungal strain COP 20242 degraded secondary cell wall layers extensively, and also degraded lignin-rich middle lamellae. Some strains of C. puteana produced soft-rot type cavities in the S2 layer. All strains of C. puteana employed in the present work showed a positive reaction to tannic acid in the Bavendamm test, indicating the production of laccase. Microscopic and enzymatic studies provided evidence to suggest that the wood decay by C. puteana is unique both in terms of micromorphological and enzymatic patterns of cell wall degradation. This is because brown-rot fungi are not generally known to form cavities in the cell walls or to produce lignin-degrading enzymes. These observations suggest that lignin degradation capacity of brown-rot fungi may be greater than previously considered.

Micromorphological characteristics of decayed wood and laccase produced by the brown-rot fungus Coniophora puteana

Rubber biosynthesis takes place on the surface of rubber particles. These particles are surrounded by a monolayer membrane in which the rubber transferase is anchored. In order to gain better insight into whether rubber particles from different plant species share common structural characteristics, the micromorphology of rubber particles from Ficus carica, Ficus benghalensis, and Hevea brasiliensis was examined by electron microscopy. Rubber particles of all three species were spherical in shape, and the size of rubber particles of H. brasiliensis was much smaller than those of F. carica and F. benghalensis. In addition, investigations were undertaken to compare the cross-reactivity of the antibody raised against either the H. brasiliensis small rubber particle protein (SRPP) which is suggested to be involved in rubber biosynthesis, or the cis-prenyltransferase (CPT) which has an activity similar to rubber transferase. Both western analysis and TEM-immunogold labelling studies showed that rubber particles of F. carica and F. benghalensis do not contain the SRPP. None of the rubber particles in F. carica, F. benghalensis and H. brasiliensis contained the CPT, suggesting that the CPT itself could not catalyse the formation of high molecular weight rubber. These results indicate that rubber particles in the three different plant species investigated share some degree of similarity in architecture, and that the SRPP and CPT themselves are not the core proteins necessary for rubber biosynthesis.

Yoon Soo Kim

Papers

Effects of gamma irradiation on morphological changes and biological responses in plants

Micromorphological characteristics of wood biodegradation in wet environments: a review

Characterization of anatomical features and silica distribution in rice husk using microscopic and micro-analytical techniques

Micromorphological characteristics of decayed wood and laccase produced by the brown-rot fungus Coniophora puteana

The micromorphology and protein characterization of rubber particles in Ficus carica, Ficus benghalensis and Hevea brasiliensis