Orientation of microfibrils and microtubules in developing tension-wood fibres of Japanese ash (Fraxinus mandshurica var. japonica)

Abstract

Abstract. The orientation of cellulose microfibrils (MFs) and the arrangement of cortical microtubules (MTs) in the developing tension-wood fibres of Japanese ash (Fraxinus mandshurica Rupr. var.japonica Maxim.) trees were investigated by electron and immunofluorescence microscopy. The MFs were deposited at an angle of about 45 ~ to the longitudinal axis of the fibre in an S-helical orientation at the initiation of secondary wall thickening. The MFs changed their orientation progressively, with clockwise rotation (viewed from the lumen side), from the S-helix until they were oriented approximately parallel to the fibre axis. This configuration can be considered as a semihelicoidal pattern. With arresting of rotation, a thick gelatinous (G-) layer was developed as a result of the repeated deposition of parallel MFs with a consistent texture. Two types of gelatinous fibre were identified on the basis of the orientation of MFs at the later stage of G-layer deposition. Microfibrils of type 1 were oriented parallel to the fibre axis; MFs of type 2 were laid down with counterclockwise rotation. The counterclockwise rotation of MFs was associated with a variation in the angle of MFs with respect to the fibre axis that ranged from 5 ~ to 25 ~ with a Z-helical orientation among the fibres. The MFs showed a high degree of parallelism at all stages of deposition during G-layer formation. No MFs with an S-helical orientation were observed in the G-layer. Based on these results, a model for the orientation and deposition of MFs in the secondary wall of tension-wood fibres with an $1 + G type of wall organization is proposed. The MT arrays changed progressively, with clockwise rotation (viewed from the lumen side), from an angle of about 35~40 ~ in a Z-helical orientation to an angle of approximately 0 ~ (parallel) to the fibre axis during G-layer formation. The parallelism between MTs and MFs was evident. The density of MTs in the developing tension-wood fibres Abbreviations: FE-SEM = field emission scanning electron microscopy; G = gelatinous layer; MF = cellulose microfibril; MT = cortical microtubule; $1 = outermost layer of the secondary wall; TEM = transmission electron microscopy Correspondence to: R. Funada; FAX: 81 (11) 736 1791 during formation of the G-layer was about 17-18 per gm of wall. It appears that MTs with a high density play a significant role in regulating the orientation of nascent MFs in the secondary walls of wood fibres. It also appears that the high degree of parallelism among MFs is closely related to the parallelism of MTs that are present at a high density.

New Techniques Enable Comparative Analysis of Microtubule Orientation, Wall Texture, and Growth Rate in Intact Roots of Arabidopsis

“…In plants, FESEMs use so far has been limited to simultaneously viewing CMTs and cell walls in partially extracted onion root tips (Vesk et al, 1994) and tobacco BY-2 cells (Vesk et al, 1996) and determining the alignment of CMFs in some woody species (Abe et al, 1995;Prodhan et al, 1995). To view the innermost layer of primary cell walls, we planed a thin layer from the frozen root surface and gently ex- tracted cytoplasmic material from the exposed cells with sodium hypochlorite.…”

“…To view the innermost layer of primary cell walls, we planed a thin layer from the frozen root surface and gently ex- tracted cytoplasmic material from the exposed cells with sodium hypochlorite. Conventional sliding microtomes are often used for cryo-sectioning (Takeda and Shibaoka, 1978;Hogetsu, 1986;Abe et al, 1995;Prodhan et al, 1995) but in this study, a cryoultramicrotome cooled to Ϫ120°C with liquid N 2 was used to prevent structural deformation by ice crystals. Dimethyl sulfoxide (DMSO) was used as a cryoprotectant for the same reason.…”

“…The innermost layer of cell wall was covered with cytoplasm, in contrast to reports for other species using replica techniques (Takeda and Shibaoka, 1978;Hogetsu, 1986), and treatment with sodium hypochlorite was found to be most effective for removing this material. What hypochlorite extracts from cells is not fully understood, although it has been used to extract cytoplasm from woody tissue (Abe et al, 1995). From its chemical structure it is likely that hypochlorite only interacts with proteins and not polysaccharides.…”

An Overview of Microfibril Angle in Fiber of Tension Wood

“…2B, 3B) [33][34][35][36][37][38]. In some species having no G-layer in reaction wood, it has been reported that microfibril angle of S2 layer decreased [15,[39][40][41][42] reported that the microfibril angle of S2 layer was very small (5 to 10 degrees) in reaction wood of Magnolia acuminate and Liriodendron tulipifera.…”

“…More detailed investigation is still needed to clarify the changes of microfibril angle in the S2 layer for many other species with three-layered secondary wall without G-layer. It is well known that microfibril angle in wood fiber gradually changes from secondary wall to G-layers [34,36,37]. In Fraxinus mandshurica, the microfibril changed its orientation angle progressively, with clockwise rotation, from the S-helix until it was oriented approximately parallel to the fiber axis [37].…”