Noritsugu Terashima

Heterogeneity in formation of lignin-XI : An autoradiographic study of the heterogeneous formation and structure of pine lignin

SummarySelective labeling of p-hydroxyphenyl-, guaiacyl-and syringylpropane moieties in protolignin was achieved by administration of corresponding 3H-labeled monolignol glucosides to differentiating xylem of pine. The growing process of the protolignin macromolecule in the specific morphological region was visualized by application of high resolution microautoradiography to the selectively labeled wood tissue.p-Hydroxyphenyl lignin is formed mainly in the compound middle lamella and cell corner in an early stage of cell wall differentiation. There are two peaks of deposition of guaiacyl lignin in the compound middle lamella at an early stage and in the secondary wall at a late stage. The content of condensed guaiacyl units is higher in the middle lamella than in the secondary wall lignin. Syringyl lignin is formed mainly in the inner layer of the secondary wall in a late stage as a minor structural moiety. During the formation of the cell wall, protolignin grows under definite biological regulations to a heterogeneous macromolecule which consists of various structural moieties arranged in a regular manner. The origin of the heterogeneous structure was explained as a result of the biogenesis of protolignin in the cell wall.

Heterogeneity in formation of lignin

SummaryThe formation of lignin in the cell wall of compression wood of Pinus thunbergii was examined by selective radio-labeling of specific structural units in the lignin and visualization of the label in the different morphological regions by microautoradiography. Deposition of lignin in the tracheid cell wall of compression wood occurred in the order: p-hydroxyphenyl, guaiacyl and syringyl lignin, which is the same order as observed in normal wood. However, the period of lignification in the compression wood was quite different from those of normal and opposite woods. The p-hydroxyphenyl units were deposited mainly in the early stage of cell wall formation in compound middle lamella in normal and opposite woods, while in compression wood, they were formed in both the compound middle lamella and the secondary wall. The most intensive lignification was observed during the formation of the S2 layer, proceeding from the outer to inner S2 layers for a long period in compression wood. In the normal or opposite woods, in contrast, the lignification became active after formation of S3 had begun, then proceeded uniformly in the secondary wall and ended after a short period.

Nanostructural assembly of cellulose, hemicellulose, and lignin in the middle layer of secondary wall of ginkgo tracheid.

Physical, chemical, and biological properties of wood depend largely on the properties of cellulose, noncellulosic polysaccharides, and lignin, and their assembly mode in the cell wall. Information on the assembly mode in the main part of the ginkgo tracheid wall (middle layer of secondary wall, S2) was drawn from the combined results obtained by physical and chemical analyses of the mechanically isolated S2 and by observation under scanning electron microscopy. A schematic model was tentatively proposed as a basic assembly mode of cell wall polymers in the softwood tracheid as follows: a bundle of cellulose microfibrils (CMFs) consisting of about 430 cellulose chains is surrounded by bead-like tubular hemicellulose-lignin modules (HLM), which keep the CMF bundles equidistant from each other. The length of one tubular module along the CMF bundle is about 16 ± 2 nm, and the thickness at its side is about 3–4 nm. In S2, hemicelluloses are distributed in a longitudinal direction along the CMF bundle and in tangential and radial directions perpendicular to the CMF bundle so that they are aligned in the lamellae of tangential and radial directions with regard to the cell wall. One HLM contains about 7000 C6-C3 units of lignin, and 4000 hexose and 2000 pentose units of hemicellulose.

Formation and Structure of Lignin in Monocotyledons IV. Deposition Process and Structural Diversity of the Lignin in the CellWall of Sugarcane and Rice Plant Studied by Ultraviolet Microscopic Spectroscopy

The ultraviolet (UV) absorption spectra of lignins in various morphological regions of growing culm of sugarcane and rice plant were recorded to examine the heterogeneous distribulion of lignin structural moieties. The spectra were compared with those of the mixture of pine milled wood lignin (MWL), pcoumaric and ferulic acid esters in different proportions. The lignification of various tissues takes place at different growing stages dcpending on the role that the tissue plays in the plant, and the lignins in different morphological regions differ in respect to the conccntration and structure. Hydroxycinnamic acids äs the characteristic structural moieties of gramineous lignin continuously deposit in the cell wall before and after the initiation of lignin deposition. The ferulic acid residue deposits more rapidly at the early stage than at the late stage of lignification, while p-coumaric acid residue deposits continuously throughout the process of lignification. The lignin in the secondary wall of protoxylem vessel consists of mostly guaiacylpropane (G) unit and less than 6% of hydroxycinnamic acid moieties, and the deposition of syringyipropane (S) unit becomes apparent at the late stage of lignification.The lignin in the cell corner of fibcr and the secondary wall of metaxylem vessel is composed of G and S units, and the proportion of S to G unit tends to increase with the progress of lignification. The lignin in the secondary wall of fiber oontains S and G units in a approximately constant ratio at every stage of lignification.

Heterogeneity in formation of lignin. XIV: Formation and structure of lignin in differentiating xylem of Ginkgo biloba

Selective labelling of p-hydroxyphenyl-, guaiacyl- and syringyl-propane moieties in protolignin was achieved by administration of corresponding 3 H-labeled monolignol glucosides to differentiating xylem of ginkgo. The growing process of the protolignin macromolecule in the specific morphological region was visualized by application of high resolution microautoradiography to the selectively labeled wood tissue. (...)

Heterogeneity in Formation of Lignin. VII. An Autoradiographic Study on the Formation of Guaiacyl and Syringyl Lignin in Poplar

Abstract Precursors of lignin biosynthesis, ferulic acid and sinapic acid labeled by 3H or 14C were administered to the differentiating xylem of poplar shoots. Biochemical interconversions between syringyl and guaiacyl type intermediates involved in the biosynthetic pathway were suppressed by administration of precursors in the dark. The process of heterogeneous deposition of guaiacyl and syringyl lignin on the cell wall was visualized by autoradiography. Guaiacyl lignin was deposited in the early stage of the xylem differentiation on the vessel wall followed by deposition of syringyl lignin on the fiber cell wall.

Heterogeneity in Formation of Lignin. X. Visualization of Lignification Process in Differentiating Xylem of Pine by Microautoradiography

Radioactive prccursors of lignin (coniferin-[ß-CJ) and hemiccllulosc (UDP-glucuronic acid-[glucuronylU-C]) were administered to growing stems of pine, and incorporation of radioactivity into differentiating xylcm was examined by microautoradiography. The lignification proceeds in threc distinct stages, always prcccded by deposition of polysaccharides. The first stage lignification occurs at the cell corner and middle lamella after the Start of thc Sj formation. The sccond stagc is a slow lignification. During this stage, the polysaccharides deposit in the S2 laycr. The main lignification occurs in the third stage after the Start of S3 formation. One of the important factors causing hetcrogcneous structure of lignin is thc fact thal the dehydrogenative polymerization of monolignol occurs in different kind of preformed polysaccharides which affcct the structure of the polymer.

Formation and Structure of Lignin in Monocotyledons. III. Heterogeneity of Sugarcane (Saccharum officinarum L.) Lignin with Respect to the Composition of Structural Units in Different Morphological Regions

Abstract Heterogeneity of sugarcane lignin with respect to the composition of structural units in different morphological regions was studied by microautoradiography and some degradative analyses. Structure of the lignin differs among fiber, vessel and parenchyma. The lignin in the secondary wall of fiber is composed of syringyl (S)-, guaiacyl (G)- and p-hydroxyphenyl (H)-propane units with accompanying phenolic acid residues, and the proportion of these monolignols is S > G > H. The lignin in vessels of protoxylem contains more G and H units than S units, and that in vessels of metaxylem is similar to that in fibers. Phenolic acid constituent in sugarcane cell wall includes sinapic acid in addition to p-coumaric and ferulic acids. Ferulic acid deposits at the very early stage of lignification, and p-coumaric and sinapic acids increasingly deposit with the progress of lignification. Therefore, the ratio of p-coumaric acid or sinapic acid to ferulic acid increases with lignification. Parenchyma wall involv...

Heterogeneity in Formation of Lignin. XIII. Formation of p-Hydroxyphenyl Lignin in Various Hardwoods Visualized by Microautoradiography

Abstract The heterogeneous nature of hardwood lignin was shown by visualizing the deposition process of p-hydroxyphenyl (H) lignin in the differentiating xylem of magnolia, beech, lilac and poplar. When p-glucocoumaryl alcohol-[arom. ring-2-3H], an efficient precursor of H units in lignin, was administered to the differentiating xylem of these trees, radioactivity was incorporated in the compound middle lamella region of vessel and fiber cell walls. The deposition of H units occurs only in the early stage of cell wall formation when the outer layer of the secondary wall is formed. H lignin deposits mainly within pectic substances and hemicellulose gel to form a highly condensed structural moiety.

On the Behavior of Monolignol Glucosides in Lignin Biosynthesis. II. Synthesis of Monolignol Glucosides Labeled with 3H at the Hydroxymethyl Group of Side Chain, and Incorporation of the Label into Magnolia and Ginkgo Lignin

For selective radio-Jabeling of specific structural units of protolignin in the cell wall, three kinds of precursor of lignin biosynthesis, /7-glucocoumaryl alcohol, coniferin and syringin labeled with H at the hydroxymethyl group of side chain (γ-position) were synthesized, and administered to magnolia and ginkgo trees. The newly formed radioactive lignin gave thioacidolysis products in which radioactivities were distributed not only in the C6-C3 units corresponding to the administered precursor but also other C6-C3 units. These results indicate that the modification of aromatic ring moiety occurs among the intermediates which retain the γ-Η. It suggests a new mechanism of modification of aromatic ring may participate in the pathway of lignin biosynthesis.