Unusual metaxylem tracheids in petioles of Amorphophallus (Araceae) giant leaves

BACKGROUND AND AIMS: Petioles of huge solitary leaves of mature plants of Amorphophallus resemble tree trunks supporting an umbrella-like crown. Since they may be 4 m tall, adaptations to water transport in the petioles are as important as adaptations to mechanical support of lamina. The petiole is a cylindrical shell composed of compact unlignified tissue with a honeycomb aerenchymatous core. In both parts numerous vascular bundles occur, which are unique because of the scarcity of lignified elements. In the xylemic part of each bundle there is a characteristic canal with unlignified walls. The xylem pecularities are described and interpreted. MATERIAL: Vascular bundles in mature petioles of Amorphophallus titanum and A. gigas plants were studied using light and scanning electron microscopy. KEY RESULTS: The xylemic canal represents a file of huge metaxylem tracheids (diameter 55-200 microm, length >30 mm) with unlignified lateral walls surrounded by turgid parenchyma cells. Only their end walls, orientated steeply, have lignified secondary thickenings. The file is accompanied by a strand of narrow tracheids with lignified bar-type secondary walls, which come into direct contact with the wide tracheid in many places along its length. CONCLUSIONS: The metaxylem tracheids in A. petioles are probably the longest and widest tracheids known. Only their end walls have lignified secondary thickenings. Tracheids are long due to enormous intercalary elongation and wide due to a transverse growth mechanism similar to that underlying formation of aerenchyma cavities. The lack of lignin in lateral walls shifts the function of 'pipe walls' to the turgid parenchyma paving the tracheid. The analogy to carinal canals of Equisetum, as well as other protoxylem lacunas is discussed. The stiff partitions between the long and wide tracheids are interpreted as structures similar to the end walls in vessels.     

Novel conducting tissues in Lower Devonian plants

Elongate cells presumed to comprise water-conducting tissues are described from the central regions of short lengths of two naked, stomatiferous, coalified, axial fossils from Lochkovian (Lower Devonian) fluvial rocks in the Welsh Borderland. In one, a discrete central strand is predominantly composed of uniformly thickened cells that are compared with central tissues in coeval plants, e.g. Aglaophyton , and the hydroids of extant mosses. The other has at least two types of cells with pits of plasmodesmata dimensions that perforate only the inner layer of a bilayered wall. These are compared with liverwort and Takakia hydroids and the coeval S-type tracheids that characterize the Rhyniopsida. The affinities of the two axes remain equivocal. The relevance of plasmodesmata-derived pits to the evolution of diversity in water-conducting elements in early cmbryophytes is discussed.     

Xylem of early angiosperms: Novel microstructure in stem tracheids of Barclaya (Nymphaeaceae)

Pit membranes of stem tracheids of all recognized species of Barclaya, an Indomalaysian genus of Nymphaeaceae, were studied with scanning electron microscopy (SEM). Pit membranes of the tracheids are composed of two thick layers, both constructed of fibrils much larger than those of tracheary elements of angiosperms other than Nymphaeaceae. The outer (distal) layer, which comprises the continuous primary wall around the tracheids, is spongiform, perforated by porosities of relatively uniform size, and confined to or most prominent on end walls of stem tracheids. The second layer consists of thick widely spaced fibrils that are oriented axially and are laid down proximally (facing the cell lumen) to the first (outer) layer, although continuous with it. These axial fibrils are attached at their ends to the pit cavities. This peculiar microstructure is not known outside Nymphaeaceae except in Brasenia and Cabomba (Cabombaceae, Nymphaeales), and has not been previously described for Barclaya. The longitudinally oriented threads and strands in perforation plates of secondary xylem of wood and stems of a variety of primitive woody angiosperms (e.g., Illicium) are not homologous to the pit membrane structure observed in stem tracheids of Barclaya, which, like other Nymphaeaceae, has only primary xylem and no perforation plates. The tracheid microstructure reported here is different from pit structures observed in any other group of vascular plants, living or fossil. The tracheid stem microstructures of Barclaya and other Nymphaeaceae appear to be a synapomorphy of Nymphaeaceae and Cabombaceae, and need further study with respect to ultrastructure and function.     

Immunolocalization and structural variations of xylan in differentiating earlywood tracheid cell walls of Cryptomeria japonica

We investigated the spatial and temporal distribution of xylans in the cell walls of differentiating earlywood tracheids of Cryptomeria japonica using two different types of monoclonal antibodies (LM10 and LM11) combined with immunomicroscopy. Xylans were first deposited in the corner of the S₁ layer in the early stages of S₁ formation in tracheids. Cell corner middle lamella also showed strong xylan labeling from the early stage of cell wall formation. During secondary cell wall formation, the innermost layer and the boundary between the S₁ and S₂ layers (S₁/S₂ region) showed weaker labeling than other parts of the cell wall. However, mature tracheids had an almost uniform distribution of xylans throughout the entire cell wall. Xylan localization labeled with LM10 antibody was stronger in the outer S₂ layer than in the inner layer, whereas xylans labeled with LM11 antibody were almost uniformly distributed in the S₂ layer. In addition, the LM10 antibody showed almost no xylan labeling in the S₁/S₂ region, whereas the LM11 antibody revealed strong xylan labeling in the S₁/S₂ region. These findings suggest that structurally different types of xylans may be deposited in the tracheid cell wall depending on the developmental stage of, or location in, the cell wall. Our study also indicates that deposition of xylans in the early stages of tracheid cell wall formation may be spatially consistent with the early stage of lignin deposition in the tracheid cell wall.     

Physiological correlates of the morphology of early vascular plants

RAVEN, J. A., 1984. Physiological correlates of the morphology of early vascular plants. The early evolution of vascular land plants is considered in relation to the physiological problems of life on land. The universal characteristics of vascular plants (xylem, cuticle, stomata, intercellular air spaces, long-distance symplastic transport and alternation of generations) are discussed in terms of the essential properties of a homoiohydric phototroph. Likely precursors of vascular plants, and the physico-chemical and biotic environment in which they occurred, are outlined prior to a discussion of the selective forces acting on the evolution of vascular plants in the Upper Silurian and Lower Devonian. Emphasis is placed on biochemical and structural 'pre-adaptations' which may have occurred in the precursors of vascular plants and on which natural selection could have acted with lignified xylem, stomata, etc., as the end-products. Guiding principles in the analysis include the physiology of extant plants, physico-chemical constraints, and compatibility with the fossil record. It is concluded that the likely sequence of acquisition of vascular plant characteristics was: heteromorphic alternation of generations with an erect sporophyte; cuticularization of sporophyte; evolution of xylem; occurrence of intercellular air spaces with pores in the epidermis; stomatal activity of the pores. Endodermis and phloem-type long-distance transport probably originated around stages (3)-(5).     

An alternative model for the earliest evolution of vascular plants

Land plants comprise the bryophytes and the polysporangiophytes. All extant polysporangiophytes are vascular plants (tracheophytes), but to date, some basalmost polysporangiophytes (also called protracheophytes) are considered non‐vascular. Protracheophytes include the Horneophytopsida and Aglaophyton/Teruelia. They are most generally considered phylogenetically intermediate between bryophytes and vascular plants and are therefore essential to elucidate the origins of current vascular floras. Here, we propose an alternative evolutionary framework for the earliest tracheophytes. The supporting evidence comes from the study of the Rhynie chert historical slides from the Natural History Museum of Lille (France). From this, we emphasize that Horneophyton has a particular type of tracheid characterized by narrow, irregular, annular and/or, possibly spiral wall thickenings of putative secondary origin, and hence that it cannot be considered non‐vascular anymore. Accordingly, our phylogenetic analysis resolves Horneophyton and allies (i.e. Horneophytopsida) within tracheophytes, but as sister to eutracheophytes (i.e. extant vascular plants). Together, horneophytes and eutracheophytes form a new clade called herein supereutracheophytes. The thin, irregular, annular to helical thickenings of Horneophyton clearly point to a sequential acquisition of the characters of water‐conducting cells. Because of their simple conducting cells and morphology, the horneophytophytes may be seen as the precursors of all extant vascular plant biodiversity.     

扁圆封印木（相似种）茎干的解剖特征

贵州省水城矿区晚二叠世煤核中扁圆封印木（相似种Ｓｉｇｉｌｌａｒｉａ ｃｆ．ｂｒａｒｄｉｉＢｒｏｎｇｎ．）茎干的主要解剖特征如下：管状中柱,具多边形薄壁细胞组成的髓。初生木质部成环带状,外缘呈规则的齿槽状,向心式发育。次生木质部显束状特征,横切面管胞为方圆至长方形,纵切面为梯状壁增厚,并具流苏纹。射线１—２列细胞宽,数个至十余个细胞高。叶迹起源于初生木质部外缘的槽中,中始式,但以向心发育为主。     

Anatomical Characteristics of the Stem of Sigillaria cf. brardii from Coal Balls in Guizhou Province,China

The stem specimens of Sigillaria cf. brardii were collected from the coal balls of Upper Permian in Shuicheng Coal Mines in Guizhou Province. The main anatomical characteristics of Sigillaria cf. brardii are described as follows: The stem is siphonostelic, with pith composed entirely of polygonal parenchyma cells, there are secondary walls in some pith cell cavities these secondary walls show the characters of cell division. Surrounding the pith is the continuous cylindrical primary xylem which consists entirely of tracheids. The outermost, and part are the protoxylem elements show spiral secondary thickenings. In cross section, the outer edge of exarch primary xylem appears regularly sinuous, with trace of mesarch leaf originating from the furrows. The centripetal metaxylem is characterized by scalariform wall thickenings on the tracheids, and delicated strands of secondary wall materials extending between abjacent bars, these structures are called fimbris, or williamson striations, and are characteristic in lepidodendrids. The secondary xylem consists of tracheids and vascular rays. The tracheids, too, have scalariform wall thickenings and fimbris. The rays are one-to twocell width and several to more than ten cells in height.     

A New Species of Araucarioxylon Kraus from the Early Early Permian,Nei Mongol,China

A kind of silicified fossil wood with mixed pits on the radial tracheid wall is described. The fossil wood was collected from the top of Taiyuan Formation (early Early Permian) in Wuda Mining District, Nei Mongol. Compared with the Paleozoic fossil woods in the world, it is put into Araucarioxylon Kraus and named as A. laoshidanense sp. nov. Based on the character of possessing mixed pittings (alternate and opposite pittings) on the radial tracheid wall, the fossil wood is believed to be one of the unknown primitive conifers.Diagnosis of the new species: Only secondary xylem preserved and consisting of axial tracheids and rays. Growth ring boundary, resin duct and axial parenchyma absent. One to Four (commonly 2or3) seriates of bordered pits mostly alternate but sometimes opposite）on the radial tracheid wall. One to Four (commonly1, rarely2 to 4) Cupressoid pits in each cross-field. Rays usually uniseriate, sometimes partly-biseriate and 2 to 39 (mainly3-5) cells high.     

Tracheid differentiation in tobacco pith cultures

Summary Sterile pith cultures of Nicotiana tabacum have been induced to form localized regions of differentiating tracheids. These localized regions have been examined by phase, fluorescence, and electron microscopy, and polarization optics. Fixation for electron microscopy was with glutaraldehyde-osmium. The differentiating tracheids develop characteristic thick cell walls which are eventually lignified. The lignifications appear to be uniform throughout the secondary wall and little or no lignin appears to be deposited in the primary walls or intercellular layer. At all stages of secondary wall deposition, the peripheral cytoplasm contains a system of microtubules which form a pattern similar to that of the developing thickenings. Within this system the microtubules are oriented, the direction of orientation mirroring that of the fibrils in the most recently deposited parts of the wall. The observations support the view that the microtubules are somehow involved in microfibril orientation. The microtubules appear to be attached to the plasma membrane which has a triple layered structure. The two electron dense layers of the plasma membrane have a particulate structure. In the differentiating tracheids at regions where secondary wall thickening has not yet been deposited numerous invaginations of the plasma membrane are observed which contain loosely organized fibrillar material. It is suggested that these are areas of localized activity of the plasma membrane and that the enzymes concerned with the final organization of the cellulose microfibrils are situated at the surface of the plasma membrane. Dictyosomes in the differentiation cells give rise to vesicles which contain fibrous material and the contents are incorporated into the cell wall. Numerous profiles characteristic of plasmodesmata are evident in sections of the secondary thickenings.Part of this work was carried out at the Osborne Memorial Laboratories, Yale University.     

水青树特殊管胞的分布位置及其形态特征的研究

针对水青树（Tetracentron sinense）中一类特殊管胞进行较为全面的观察研究,判断细胞种类并分析维管组织输导机理及树木进化过程中的细胞演化规律。通过切片和解离技术,借助光学显微镜和电子显微镜对34年生水青树特殊管胞的分布位置和形态特征进行观察。结果表明：(1)特殊管胞在树木水平方向自内向外径向呈串排列,并贯穿年轮界限,多为一列,少数两列,且较为稀见。每个特殊管胞弦向左右两侧或单侧均与木射线细胞相连通。纵向上,特殊管胞单独或数个上下端接相连。(2)特殊管胞主要有以下3种类型：无端壁的纺锤形,有一个倾斜端壁,以及有两个倾斜端壁。特殊管胞的平均长度为286.44μm;横切面为四边形,平均弦向宽度为55.22μm,其平均壁厚为1.53μm。(3)特殊管胞两端封闭,无穿孔。(4)特殊管胞侧面壁上的纹孔数量较多且纹孔膜明显可见,具体表现为：弦面壁上布满特殊管胞之间的具缘纹孔,呈对列、互列偶见梯状排列;径面壁上存在与射线细胞间的具狭缘单纹孔,呈大圆形至椭圆形,每区域多为2～10个纹孔,呈1～4排横列;径面壁上与正常管胞间几无纹孔。水青树特殊管胞分布有一定规律,其长度远小于水青树正常管胞...     

内蒙古早二叠世早期南洋杉型木属一新种

报道了一种具混合型纹孔（互列式纹孔和对列式纹孔）的化石本。化石木产自内蒙古乌达矿区老石旦矿附近太原组上部,地质时代为早二叠世早期。经比较,确认为南洋杉型木属（Ａｒａｕｃａｒｉｏｘｙｌｏｎ Ｋｒａｕｓ）一种新;老石旦南洋杉型木（Ａｒａｕｃａｒｉｏｘｙｌｏｎ ｌａｏｓｈｉｄａｎｅｎｓｅ ｓｐ．ｎｏｖ．）．根据混合型纹孔的存在及其他特征,认为新种可能代表了一种原始的松杉类植物的木材化石。主要特征：仅保存     

Occurrence of the primary cell wall polysaccharide rhamnogalacturonan II in pteridophytes, lycophytes, and bryophytes. Implications for the evolution of vascular plants

Borate ester cross-linking of the cell wall pectic polysaccharide rhamnogalacturonan II (RG-II) is required for the growth and development of angiosperms and gymnosperms. Here, we report that the amounts of borate cross-linked RG-II present in the sporophyte primary walls of members of the most primitive extant vascular plant groups (Lycopsida, Filicopsida, Equisetopsida, and Psilopsida) are comparable with the amounts of RG-II in the primary walls of angiosperms. By contrast, the gametophyte generation of members of the avascular bryophytes (Bryopsida, Hepaticopsida, and Anthocerotopsida) have primary walls that contain small amounts (approximately 1% of the amounts of RG-II present in angiosperm walls) of an RG-II-like polysaccharide. The glycosyl sequence of RG-II is conserved in vascular plants, but these RG-IIs are not identical because the non-reducing L-rhamnosyl residue present on the aceric acid-containing side chain of RG-II of all previously studied plants is replaced by a 3-O-methyl rhamnosyl residue in the RG-IIs isolated from Lycopodium tristachyum, Ceratopteris thalictroides, Platycerium bifurcatum, and Psilotum nudum. Our data indicate that the amount of RG-II incorporated into the walls of plants increased during the evolution of vascular plants from their bryophyte-like ancestors. Thus, the acquisition of a boron-dependent growth habit may be correlated with the ability of vascular plants to maintain upright growth and to form lignified secondary walls. The conserved structures of pteridophyte, lycophyte, and angiosperm RG-IIs suggests that the genes and proteins responsible for the biosynthesis of this polysaccharide appeared early in land plant evolution and that RG-II has a fundamental role in wall structure.     

Ascorbic acid and xylem development in trunks of the Siberian larch trees

The contents of ascorbic acid (AA) and its oxidized form, dehydroascorbic acid (DHA), were assessed as related to the tracheid differentiation in the course of early and late wood development in the Siberian larch (Larix sibirica Ldb.) trees. The samples of the cambium, cell enlargement zone and mature cells were collected at the successive developmental stages by scraping tissues off layer by layer from trunk segments of the 20-year-old trees according to anatomical and histochemical criteria. While cambium initials were rapidly dividing, the AA contents per dry weight and per cell considerably exceeded the corresponding values characteristic of the late xylem development; such difference corresponded to the higher number of early tracheids per annual ring, as compared to the late tracheids. The AA content decreased as cells enlarged. The radial growth of the early wood tracheids, as compared to the late wood tracheids, was accompanied with a threefold increase in the AA and a decline in the DHA contents. The AA/DHA ratio was in line with the early tracheid enlargement. The maximum AA content was observed at the early stage of the secondary cell wall thickening in the tracheids of early and late xylem preceding lignification. During this stage of early wood development, the DHA content exceeded sixfold the corresponding value in the late xylem; as a result, the initial rates of lignification were different in two tissues. The rate of lignification in a newly developing layer of the early xylem increased gradually and was the highest in the completely differentiated tracheids. In the late xylem, the lignification rate was at its highest at the very beginning and then declined in the course of tracheid maturation. The dissimilar patterns of lignification in the early and late xylem were primarily associated with the DHA content, which increased in the early xylem and decreased in the maturing late xylem. Thus, the AA content and its accessibility to oxidation in the growing and mature xylem cells exhibited the diverse developmental patterns in the early and late xylem: two tissues differed in the tracheid number and radial diameter as well as in the rate of lignification.Translated from Fiziologiya Rastenii, Vol. 52, No. 1, 2005, pp. 97–107.Original Russian Text Copyright © 2005 by Antonova, Chaplygina, Varaksina, Stasova.     

Major transitions in the evolution of early land plants: a bryological perspective

Background Molecular phylogeny has resolved the liverworts as the earliest-divergent clade of land plants and mosses as the sister group to hornworts plus tracheophytes, with alternative topologies resolving the hornworts as sister to mosses plus tracheophytes less well supported. The tracheophytes plus fossil plants putatively lacking lignified vascular tissue form the polysporangiophyte clade. Scope This paper reviews phylogenetic, developmental, anatomical, genetic and paleontological data with the aim of reconstructing the succession of events that shaped major land plant lineages. Conclusions Fundamental land plant characters primarily evolved in the bryophyte grade, and hence the key to a better understanding of the early evolution of land plants is in bryophytes. The last common ancestor of land plants was probably a leafless axial gametophyte bearing simple unisporangiate sporophytes. Water-conducting tissue, if present, was restricted to the gametophyte and presumably consisted of perforate cells similar to those in the early-divergent bryophytes Haplomitrium and Takakia. Stomata were a sporophyte innovation with the possible ancestral functions of producing a transpiration-driven flow of water and solutes from the parental gametophyte and facilitating spore separation before release. Stomata in mosses, hornworts and polysporangiophytes are viewed as homologous, and hence these three lineages are collectively referred to as the 'stomatophytes'. An indeterminate sporophyte body (the sporophyte shoot) developing from an apical meristem was the key innovation in polysporangiophytes. Poikilohydry is the ancestral condition in land plants; homoiohydry evolved in the sporophyte of polysporangiophytes. Fungal symbiotic associations ancestral to modern arbuscular mycorrhizas evolved in the gametophytic generation before the separation of major present-living lineages. Hydroids are imperforate water-conducting cells specific to advanced mosses. Xylem vascular cells in polysporangiophytes arose either from perforate cells or de novo. Food-conducting cells were a very early innovation in land plant evolution. The inferences presented here await testing by molecular genetics.     

Characterization and genetic mapping of a mutation (ms35) which prevents anther dehiscence in Arabidopsis thaliana by affecting secondary wall thickening in the endothecium

The male sterile mutant, ms35 , of Arabidopsis thaliana was produced by X-irradiation of seeds. The mutant produces fertile pollen, but is male sterile because the anthers do not dehisce. Anther development in ms35 plants occurs as in wild-type Arabidopsis until shortly after microspores are released from meiotic tetrads. Thereafter, in the wild type, bands of lignified, cellulosic secondary wall thickenings are laid down around the cells of the anther endothecium. In contrast, wall thickenings are not formed in the endothecium of the ms35 mutant. Development of other lignified tissues, for example the vascular tissue of the stamen, occurs normally in ms35 plants. In mutant anthers, as pollen maturation is completed, the stomium is cleaved but the anther wall does not retract to release pollen. The block in anther dehiscence in ms35 plants is specifically correlated with the absence of endothecial wall thickenings. The ms35 mutation represents the first genetic evidence in support of the proposed role of the endothecium in anther dehiscence. The ms35 gene was mapped to the top arm of chromosome 3 ( hy2 -(4.17±2.31 cM)- ms35 -(32.14±5.45 cM)- gl1 ).     

Ultrastructure of the innermost surface of differentiating normal and compression wood tracheids as revealed by field emission scanning electron microscopy

The ultrastructure of the innermost surface of Cryptomeria japonica differentiating normal wood (NW) and compression wood (CW) was comparatively investigated by field emission electron microscopy (FE-SEM) combined with enzymatic degradation of hemicelluloses. Cellulose microfibril (CMF) bundles were readily observed in NW tracheids in the early stage of secondary cell wall formation, but not in CW tracheids because of the heavy accumulation of amorphous materials composed mainly of galactans and lignin. This result suggests that the ultrastructural deposition of cell wall components in the tracheid cell wall differ between NW and CW from the early stage of secondary cell wall formation. Delignified NW and CW tracheids showed similar structural changes during differentiating stages after xylanase or β-mannanase treatment, whereas they exhibited clear differences in ultrastructure in mature stages. Although thin CMF bundles were exposed in both delignified mature NW and CW tracheids by xylanase treatment, ultrastructural changes following β-mannanase treatment were only observed in CW tracheids. CW tracheids also showed different degradation patterns between xylanase and β-mannanase. CMF bundles showed a smooth surface in delignified mature CW tracheids treated with xylanase, whereas they had an uneven surface in delignified mature CW tracheids treated with β-mannanase, indicating that the uneven surface of CMF bundles was related to xylans. The present results suggest that ultrastructural deposition and organization of lignin and hemicelluloses in CW tracheids may differ from those of NW tracheids.     

Xylem of early angiosperms: Nuphar (Nymphaeaceae) has novel tracheid microstructure1

SEM studies of xylem of stems of Nuphar reveal a novel feature, not previously reported for any angiosperm. Pit membranes of tracheid end walls are composed of coarse fibrils, densest on the distal (outside surface, facing the pit of an adjacent cell) surface of the pit membrane of a tracheid, thinner, and disposed at various levels on the lumen side of a pit membrane. The fibrils tend to be randomly oriented on the distal face of the pit membrane; the innermost fibrils facing the lumen take the form of longitudinally oriented strands. Where most abundantly present, the fibrils tend to be disposed in a spongiform, three-dimensional pattern. Pores that interconnect tracheids are present within the fibrillar meshwork. Pit membranes on lateral walls of stem tracheids bear variously diminished versions of this pattern. Pits of root tracheids are unlike those of stems in that the lumen side of pit membranes bears a reticulum revealed on the outer surface of the tracheid after most of the thickness of a pit membrane is shaved away by the sectioning process. No fibrillar texturing is visible on the root tracheid pits when they are viewed from the inside of a tracheid. Tracheid end walls of roots do contain pores of various sizes in pit membranes. These root and stem patterns were seen in six species representing the two sections of Nuphar, plus one intersectional hybrid, as well as in one collection of Nymphaea, included for purposes of comparison. Differences between root and stem tracheids with respect to microstructure are consistent in all species studied. Microstructural patterns reported here for stem tracheid pits of Nymphaeaceae are not like those of Chloranthaceae, Illiciaceae, or other basal angiosperms. They are not referable to any of the patterns reported for early vascular plants. The adaptational nature of the pit membrane structure in these tracheids is not apparent; microstructure of pit membranes in basal angiosperms is more diverse than thought prior to study with SEM.