The structure of intervascular pits, located at the boundary between the outermost and the second youngest annual rings in Betula platyphylla var. japonica and Fraxinus mandshurica var. japonica was examined by field-emission scanning electron microscopy. Unilaterally compound pits were present in the intervascular common wall at the annual ring boundary in both species. On the outer annual ring side of the unilaterally compound pits, outlines of pit membranes were curved or trifoliate, and each pit aperture was often elongated and curved. The porosity of the intervascular pit membranes differed between the two species. In B. platyphylla var. japonica, microfibrils were loosely packed in the peripheral region of each pit membrane, and openings of up to 300 nm in width were observed. By contrast, microfibrils were densely packed throughout the entire pit membranes in F. mandshurica var. japonica, and no openings perforating the pit membranes entirely were found. In addition, each species exhibited some unique features. In B. platyphylla var. japonica, extensive ethanol-soluble material was detected not only in the intervascular pits but also on scalariform perforation plates. In F. mandshurica var. japonica, we observed fine curly fibrils of unkown chemical composition in the intervascular pit membranes.
Structural variations and secondary changes in intervascular, interfibre, interparenchyma, vessel-parenchyma, and fibre-parenchyma pit membranes, from the outermost sapwood to the inner heartwood of Fraxinus mandshurica var.japonica, were studied by uitraviolet light microscopy, and by scanning and transmission electron microscopy. In the sapwood, none of the pit membranes appeared lignified and pit membranes were seldorn incrusted. In the heartwood, material that strongly absorbed ultraviolet light was heavily deposited on intervascular, interparenchyma, vessel-parenchyma, and fibre-parenchyma pit membranes. Secondary changes in the interfibre pit pairs were not so pronounced. Interfibre pit membranes were often absent in both the sapwood and the heartwood.
Bordered pit membranes of Cryptomeria japonica were examined successively from the outermost sapwood to the heartwood by scanning electron microscopy and by ultraviolet microspectrophotometry in an attempt to evaluate the time course of the secondary deposition of incrusting materials and to gain clues to their chemical composition. Scanning electron microscopy revealed that the bordered pit membranes were covered by incrusting materials from the middle layer of the sapwood to the heartwood. Both the amount and the appearance of the deposited incrusting materials differed among four regions of the wood, namely, the middle to inner layer of the sapwood, the innermost layer of the sapwood, the intermediate wood and the heartwood. From our results it appears that, in C. japonica, incrusting materials are deposited on bordered pit membranes by stages over several years. Apparent absorption of ultraviolet light by the bordered pit membranes was detected in the analysis of the innermost layer of the sapwood, the intermediate wood and the heartwood. The incrusting materials deposited in these zones were probably phenolic compounds. However, differences in the manner and extent of the absorption of ultraviolet light were found between these three regions of the wood. The results of microspectrophotometric analysis also suggested the phased deposition of incrusting materials at the bordered pit membranes of C. japonica.
Water conduction and wood anatomy of Salix sachalinensis attacked by watermark disease were investigated. The internal symptom, the watermark, appeared as a brown to brown-black stained zone in sapwood. Dye injection tests revealed that water conduction did not take place in the watermark. However, soft X-ray photography and cryo-scanning electron microscopy revealed that the watermark had a high moisture level. In the watermark, some of the vessels were plugged with tyloses and masses of bacteria, and some of the ray parenchyma cells caused necrosis. Hence, the non-conductive watermark in sapwood can be considered similar to discoloured wood or wetwood.
This study reports on the occurrence and structure of tyloses in Fraxinus mandshurica Rupr. var. japonica Maxim. and Kalopanax pictus Nakai. Tyloses occurred in the outer sapwood of both species, but they showed great structural differences. Tyloses of F. mandshurica var. japonica were unique in their morphology and fine structure: thinwalled, highly lignified, multi-Iamellate, lacking parallel arrangement of microfibrils and intercellular layers; they are destroyed simultaneously with the transition from sapwood to heartwood. On the other hand, in K. pictus the cell wall organisation of tyloses was similar to those of anormal cell wall; both primary and secondary walllayers, and intercellular layers were found, and the tyloses tightly occluded vessels in both the sapwood and heartwood.
Betula species have phellems with distinctive features such as stratification into thin paper-like layers, which are easily split in the tangential direction, and linear lenticels. We aimed to clarify the structure and development of the characteristic phellems of B. maximowicziana. In a normal periderm, phellem, phellogen, and phelloderm consist of tangentially elongated cells that are arranged in radial files. The phellem consists of layers of 1.4 ± 0.5 cells thick of very thin-walled phellem cells alternating with layers of 7.1 ± 1.5 thick-walled phellem cells. Seasonal sampling showed that the former and the latter were formed in the early and middle-to-late stages of the growing period, respectively. In lenticels, filling tissues alternated with closing layers. Most cells were collapsed and loosely packed in the filling tissue while all cells were intact and arranged in radial files in the closing layers. The filling tissue cells had unique walls that appeared to be easily deformed. Each annual increment of phellem in Betula is composed of a thin-walled cell layer (early phellem) and a thicker layer of thick-walled cells (late phellem). It is likely that the combination of filling tissue and closing layer in lenticels helps to perform the dual functions of gas exchange and protection, and that the collapse of the cells in filling tissue effectively contributes to gas permeability.
An examination was made of the fine structure of bordered pit membranes in the radial walls between tracheids in the outer sapwood of Abies sachalinensis to improve our understanding of the so-called extended torus, the minute holes in the torus and the imperforate zone near the periphery of the pit membranes, Field-emission scanning electron microscopy revealed that a so-called extended torus was present in many bordered pit membranes. We examined the frequency occurrence of and variations in the extended torus within a single annual ring. The frequency tended to increase from the earlywood to the latewood within a single annual ring. In the tori of many bordered pit membranes, we detected minute holes, and the number and location of such minute holes in a single torus varied among individual pit membranes. The appearance of each minute hole also varied. An imperforate zone was observed near the periphery of the pit membrane. In this imperforate zone, we found amorphous materials, and fine fibrils were visible that were an extension of the fibrillar meshwork of the margo.
A resin-casting method with subsequent scanning electron microscopy (SEM) was used to examine the three-dimensional (3-D) shapes of cells and the cell walls of cambium and differentiating xylem. Glutaraldehyde- fixed and dehydrated specimens were embedded in polystyrene and then organic material was removed by digestion with acidic solutions or enzymes. The acidic solutions used for treatment were sulphuric acid and a mixture of acetic acid and hydrogen peroxide and the enzymes used for treatment were pectinase and cellulase, with a final treatment with sodium hypochlorite. Both methods could be used for studies of the differentiation of cambial cells; however, digestion with enzymes allowed better preservation of the 3-D organisation of the tissue. Negative replicas of inner surfaces of cell walls of differentiating vessel elements revealed the sequential stages of the development of bordered pits and perforation plates. Future bordered pits at the early stages of the differentiation of cell walls were demarcated by the accumulation of organic material between adjacent pit membranes. Subsequent deposition of cell wall material resulted in formation of pit cavities and the rims of perforation plates.
Morphological changes and the timing of disappearance of individual organelles provide key information for understanding the mechanism of cell death. The disappearance of microtubules, nuclei and starch grains was monitored during the death of long-lived ray parenchyma cells in the conifer Abies sachalinensis. From the eighth to the tenth annual ring from the cambium, morphological changes occurred in ray parenchyma cells and organelles disappeared. Morphological changes in nuclei became apparent first. Then microtubules disappeared and, finally, nuclei disappeared. Therefore, microtubules might play an important role during the death of ray parenchyma cells. The timing of the disappearance of starch grains differed among individual ray parenchyma cells. This result indicates that the timing of the loss of storage function in ray parenchyma cells might not depend on the progress of cell death. The possible role of microtubules during cell death of long-lived ray parenchyma cells that might differ from cell death of short-lived ray tracheids is discussed.