We examined the orientation of cellulose microfibrils (Mfs) in the cell walls of tracheids in some conifer species by field emission-scanning electron microscopy (FE-SEM) and developed a model on the basis of our observations. Mfs depositing on the primary walls in differentiating tracheids were not well-ordered. The predominant orientation of the Mfs changed from longitudinal to transverse, as the differentiation of tracheids proceeded. The first Mfs to be deposited in the outer layer of the secondary wall (S1 layer) were arranged as an S-helix. Then the orientation of Mfs changed gradually, with rotation in the clockwise direction as viewed from the lumen side of tracheids, from the outermost to the innermost S1 layer. Mfs in the middle layer of the secondary wall (S2 layer) were oriented in a steep Z-helix with a deviation of less than 15° within the layer. The orientation of Mfs in the inner layer of the secondary wall (S3 layer) changed, with rotation in a counterclockwise direction as viewed from the lumen side, from the outermost to the innermost S3 layer. The angle of orientation of Mfs that were deposited on the innermost S3 layer varied among tracheids from 40° in a Z-helix to 20° in an S-helix.
Field emission scanning electron microscopy was used to observe the inner surfaces of the developing secondary walls of earlywood tracheids of Abies sachalinensis Masters. Microfibrillar orientation in the secondary wall, as seen from the lumen side, changed in a clockwise direction from the outermost S1 to the middle of the S2 and from there counter-clockwise to the innermost S3. Sometimes microfibrils oriented in a steep S-helix were observed in the S3 layer. Lamellae showing different microfibrillar orientations in wall layers other than the S2 were observed beneath newly deposited microfibrils on the inner surface of the developing wall. Furthermore, on the inner surface of the wall forming the S12, S23 and S3, lamellae with microfibrils closely aligned at the same angle as one another and lacking spaces were not observed. These observations suggest that in layers other than the S2 most lamellae are not composed of closely spaced microfibrils.
The orientation of the microfibri1s deposited on the innermost surfaces of the tracheid wall was observed in three conifer species, Larix leptolepis, Picea jezoensis, and Picea abies, using field emission scanning electron microscopy (FE-SEM). The microfibrillar orientation is different in each tracheid and exhibits either an S- or a Z-helix. The latest microfibrils deposited were normally joined into small bundles having various widths and had a different orientation from the microfibrils beneath them. When the latest deposited microfibrils on the innermost surface were oriented in an S-helix, the microfibrils beneath them were oriented in either a flatter S-helix or in a Z-helix, and when they were oriented in a Z-helix, the microfibrils beneath them were oriented in a steeper Z-helix. This is because, as seen from the lumen side, the microfibrillar orientation changes counterclockwise from the outer S23 to the innermost S3. These microfibrillar orientations varied throughout a single annual ring in each of the three species. The commonly observed angles of these microfibril were: Larix leptolepis: 70-80°, Picea jezoensis: 60-70°, and Picea abies: 40-50° in an S-helix, and the maximum range of angles was limited in extent to about 90 degrees in all species.
A quantitative scanning electron microscopic (SEM) study of the changes in microtubule orientations and arrays during secondary wall formation has been done on conifer (Abies sachalinensis Masters) tracheids. Microtubules have similar orientations as the microfibrils being deposited in the various wall layers. The density of microtubules is different in different stages of secondary cell wall formation. Microtubules are more closely arrayed in the tracheids forming the S2 than the S12 and S3. During S3 formation, sometimes 2-7 microtubules are closely arrayed, and form bundles about 80-350 nm wide. Bundles of microfibrils of similar width were also observed during S3 formation.
Changes in the quantity and quality of DNA during storage (0, 1, 3, 5, 11, 15, 23, 27, 40, 44, 75 years) were investigated for the wood of Cryptomeria japonica. Fresh sapwood yielded more DNA than fresh heartwood. The amount of DNA extracted from wood samples stored for 1 year or more after cutting was below the limit of detection by measurement with a UV spectrophotometer. A chloroplast DNA region with a length of 527 bp was amplified by the polymerase chain reaction from the DNA extracted from sapwood stored for 0, 1, 3, 5, 11, 15 and 23 years, and from heartwood stored for 0, 3, 11, 15 and 23 years. A shorter length of chloroplast DNA with a length of 82 bp was amplified for all of the wood samples used in this study. Using fluorescence microscopy, we observed changes in the abundance of cell organelles containing DNA such as nuclei and amyloplasts during storage. Microscopy showed that the DNA content of latewood ray parenchyma was greater than the DNA content of earlywood ray parenchyma in the sapwood, and amyloplasts were present in ray cells in the heartwood of the stored wood. Our results suggest that optimizing DNA extraction protocols for wood stored for long periods will improve the utility DNA identification of wood products.
We investigated radial resin canals in Pinus densiflora by means of serial tangential sections taken from phloem to xylem through the cambium. The canals were found within fusiform rays in both phloem and xylem. The ducts were closed in the cambial zone, but opened at widely differing distances from the cambium among individual radial resin canals, ranging from 120 to 340 μm on the phloem side and from 260 to 640 μm on the xylem side. Further, the ducts were not open continuously on both sides. The average number of radial resin canals in the tangential plane was 0.76/mm2. In the cambial zone, central cells of fusiform rays which might develop into epithelial cells later, were smaller and more deeply stained than the surrounding ray initial cells, allowing them to be identified at the initial stage. Two or more radial resin canals situated nearby each other were connected through an axial resin canal.
The initial uptake of water by small fragments of compressed and drying- set wood of Cryptomeria japonica D. Don was monitored by confocal laser scanning microscopy (CLSM) using an aqueous solution of the fluorescent dye acridine orange. CLSM allowed visualization of the recovery over time of compressed and drying-set wood and the uptake of water by the specimens. Furthermore, CLSM allowed us to monitor the structure of deformed tracheids under atmospheric conditions. Increases in the compression ratio increased the time required for the uptake of water. The uptake of water was detected first between deformed and undeformed regions of compressed and drying-set wood at all compression ratios tested.
The cellular distribution of heartwood substances and the structure of the pathways for their diffusion were studied in Acacia mangium Willd. Apart from ray parenchyma cells, axial parenchyma cells also are involved in the formation of heartwood substances. Heartwood substances were unevenly distributed in the heartwood. A closer inspection of interfibre pit pairs revealed that, although many pit membranes were completely covered with encrusting materials, some pit pairs had many small openings on their pit membranes. The openings possibly function as intercellular diffusion pathways for heartwood substances. The sizes of the pits varied considerably, ranging from 0.4 to 2.3 μm in diameter. These structural variations in the interfiber pits might be one of the factors contributing to the uneven distribution of the heartwood substances. A large number of blind pits were present in the ray parenchyma cells and faced the intercellular spaces, into which heartwood substances from the ray parenchyma cells were released via these blind pits. Resin-cast replicas demonstrated that the intercellular spaces and the blind pits formed a three-dimensional network that is considered to serve as an extracellular diffusion pathway for heartwood substances.