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.
Cytochemical changes in cambia! cell walls were studied during the transition from rest to mitotic activity in spring. A partial autolysis occurred in the radial walls especially at cell junctions. The lysis was closely associated with a localised decrease in the level of calcium ions bound to the cell walls.
The seasonal process of early- and latewood formation at different stern heights was examined in 20-year-old Pinus densiflora trees having different crown proportions. The initiation of tracheid production did not appear to vary among trees or within sterns; however, the transition to latewood formation and cessation of tracheid production began earlier at the lower stern. This tendency was more obvious in trees with smaller crowns. The duration and rate of tracheid production in early- and latewood also differed among trees with different crown proportions and within sterns. It is suggested that the quantitative distribution of latewood along the trunk are attributable not only to the date of transition from earlywood to latewood, but also to the duration and rate of latewood tracheid production.
We examined the three-dimensional (3-D) structure of differentiating xylem in a hardwood tree, Kalopanax pictus, by confocallaser scanning microscopy (CLSM) using relatively thick, hand-cut histological sections. 3-D studies of plant tissues by mechanical serial sectioning with a microtome are very time-con suming. By contrast, the preparation of samples for CLSM is easier and the 3-D structure of intact tissue is preserved during optical sectioning. We obtained extended-focus images of the surface of specimens and these images resembled the stereographic images obtained by scanning electron microscopy. In addition , we observed radial files of cambial derivative cells at various stages of differenti ation and the internal structure along the 'z' axis of specimens on serial optical sections. We analysed the developmental changes in the morphology of cambial derivat ive cells, for example, the 3-D shape and arrangement of cells, the readjustment of the position of cells, and the development of secondary walls, pits and perforation plates. Our results showed that the arrangement of the differentiating xylem cells mirror s that of the cambial cell s. Deviations from the longitudinal orientation of vessel elements were specified by similar patterns of orientation of fusiform and ray cambial cells. The development of vessel elements progressed more rapidly than that of other xylem elements. When secondary walls with bordered pits and perforation plates with membranes were present in vessel elements and their expansion ceased, no secondary wall formation was detected in adjacent ray cells. The delay in secondary wall formation by the ray parenchyma cells, as compared to that by vessel elements, might facilitate the readju stment of the position of cells in the developing xylem tissue that is a consequence of the considerable expan sion of the vessel elements.
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.
This paper reviews the development of xylem vessels in ring-porous dicots and the corresponding leaf phenology. Also included are our original observations on the time-course of vessel element growth, secondary wall deposition, and end wall perforation in the deciduous hardwood Kalopanax septemlobus. Different patterns of xylem growth and phenology serve different strategies of the species for adaptation to seasonal climates. Trees with ring-porous xylem form wide earlywood vessels (EWV) in spring and narrow latewood vessels in summer. The wide EWV become embolized or blocked with tyloses by the end of the growing season while the narrow vessels may remain functional for many years. The co-occurrence of wide and narrow vessels provides both efficiency and safety of the water transport as well as a potentially longer growing season. It has for a long time been assumed that EWV in ring-porous hardwoods are formed in early spring before bud burst in order to supply sap to growing leaves and shoots.
However, the full time-course of development of EWV elements from initiation of growth until maturation for water transport has not been adequately studied until recently. Our observations clarify a crucial relationship between leaf maturation and the maturation of earlywood vessels for sap transport. Accumulated new evidence shows that EWV in branches and upper stem parts develop earlier than EWV lower in the stem. The first EWV elements are fully expanded with differentiated secondary walls by the time of bud burst. In lower stem parts, perforations in vessel end walls are formed after bud burst and before the new leaves have achieved full size. Therefore, the current-year EWV network becomes functional for water transport only by the time when the first new leaves are mature.
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.
We analyzed the chemical composition of vestures of vessel elements and wood fibres of Eucalyptus camaldulensis and Eucalyptus globulus by ultraviolet (UV) microscopy, transmission electron microscopy (TEM) after staining with potassium permanganate (KMnO4) or the PATAg reaction, and field-emission scanning electron microscopy (FE-SEM). Samples were treated with dilute solutions of NaOH at various concentrations. Before treatment with alkali, the vestures on the secondary walls of vessel elements and wood fibres were visible on UV micrographs taken at 280 nm and were strongly stained by KMnO4. Vestures were strongly stained by the PATAg reaction in samples that had been treated with 0.1% NaOH. However, treatment with higher concentrations of NaOH dissolved the vestures. FE-SEM observations showed that the process of dissolution of vestures during alkali extraction differed between the two species. It appears that vestures in Eucalyptus woods consist mainly of alkali-soluble polyphenols and polysaccharides. In addition, the chemical composition of vestures may differ between the two species of Eucalyptus that we examined.
The anatomical characteristics of Nectria canker on Fraxinus mandshurica var. japonica were analyzed. Typical cankers were conspicuous, round to oval, with uniform concentric rings of affected xylem in a target-like structure. Each concentric annual growth ring was wider than the corresponding annual rings lateral to the cankers. The xylem elements were extremely disoriented. The cambial zone became discontinuous and disappeared. An inoculation test with the causal fungus, Nectria galligena, produced similar anatomical abnormalities and revealed the process of canker formation. Fewer and narrower vessels were formed, and water conduction took place only in the large vessels of the current year in the cankers.