Comparative wood anatomy in Abietoideae (Pinaceae)

This study, which includes 51 species and six genera of subfamily Abietoideae (Pinaceae), assesses the systematic significance of the wood structure in this group. In particular, the presence of normal and traumatic resin canals, the ray structure and the axial parenchyma constitute phylogenetically informative features. Comparative wood anatomy of Abietoideae clearly supports the monophyly of the genera Abies–Cedrus–Keteleeria–Nothotsuga–Pseudolarix–Tsuga, all of which have axial parenchyma with nodular transverse end walls in the regions of growth ring boundaries, crystals in the ray parenchyma and pitted horizontal and nodular end walls of ray parenchyma cells. Axial resin canals support a subdivision of the subfamily into two groups: Abies, Cedrus, Pseudolarix and Tsuga, without axial resin canals, and Keteleeria and Nothotsuga, with axial resin canals and a specific arrangement of traumatic axial resin canals. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 160 , 184–196.     

Le phloème deSelaginella willdenowii: histophysiologie comparée

Metaphloem sieve elements ofSelaginella willdenowii are elongated cells with slightly oblique or transverse end walls. Pores are seen on both lateral and end walls, although they are more numerous on the latter. Parenchyma cells exhibiting strong enzyme activities (acid phosphatase, non specific esterase, succinate dehydrogenase, cytochrome oxidase, peroxidase) are present between sieve elements and tracheids in each vascular bundle. A functional association thus appears to exist between these parenchyma cells and the conducting elements.—The occurrence of transverse to slightly oblique end walls in sieve elements seems to characterize the ligulate Lycopsids (as opposed to the aligulateLycopodium where sieve elements possess slanting, very oblique, end walls).

     

Vessel diameter is related to amount and spatial arrangement of axial parenchyma in woody angiosperms

Parenchyma represents a critically important living tissue in the sapwood of the secondary xylem of woody angiosperms. Considering various interactions between parenchyma and water transporting vessels, we hypothesize a structure–function relationship between both cell types. Through a generalized additive mixed model approach based on 2,332 woody angiosperm species derived from the literature, we explored the relationship between the proportion and spatial distribution of ray and axial parenchyma and vessel size, while controlling for maximum plant height and a range of climatic factors. When factoring in maximum plant height, we found that with increasing mean annual temperatures, mean vessel diameter showed a positive correlation with axial parenchyma proportion and arrangement, but not for ray parenchyma. Species with a high axial parenchyma tissue fraction tend to have wide vessels, with most of the parenchyma packed around vessels, whereas species with small diameter vessels show a reduced amount of axial parenchyma that is not directly connected to vessels. This finding provides evidence for independent functions of axial parenchyma and ray parenchyma in large vesselled species and further supports a strong role for axial parenchyma in long‐distance xylem water transport.     

The ontogeny of the vascular cambium inGinkgo biloba roots

Observation was made on early ontogeny of vascular cambium in the developing root ofGinkgo biloba L. After completion of root elongation, the vascular meristem gradually acquires cambial characteristics. Strips of the periclinal division of cells in transverse section are observed on the inner side of phloem when the primary xylem and phloem in the stele have been established. The strips are united into a continuous layer between phloem and xylem. In tangenital section, the procambium shows a homogeneous structure, which is initially composed of short cells with transverse end walls and subsequently, of long cells with tapering ends. Then, the procambium is organized into two systems of cells; axial strands of short cells with transverse end walls resulting from the sporadic transverse divisions of long cells, and long cells with tapering ends. Still later, the short cells are divided frequently in a trasverse plane exhibiting one or a few cells in width and several decades of cells in height, while the long cells are elongated. The frequency of transverse divisions of the short cells decreases in subsequent stages. Eventually, the short cells in axial strands are vertically separated from one another by the elongation of neighboring long cells and by the decrease in the frequency of transverse divisions of short cells themselves. Cambial initials occur in two forms; ray initials a few cells in height and one cell in width derived from the short cells, and fusiform initials with tapering ends derived from the long cells.     

Cell wall structure in the xylem parenchyma ofCryptomeria

Summary Cell wall structure in ray and axial parenchyma cells in the wood ofCryptomeria was shown to be typically crossed polylamellate and dissimilar to the characteristically layered wall of fibers and tracheids. Ray cells differed from axial cells in terms of form and also in the relative inclination of crossed microfibrillar helices in the cell wall. This feature was reflected by positive birefringence in ray cells and negative birefringence in axial cells. Localized wall thickenings,viz. transverse bars in ray cells and longitudinal ribs in axial cells, also displayed crossed polylamellate structure. This observation contrasts with the exclusively longitudinal microfibrillar orientation previously reported for longitudinal ribs in elongated parenchyma cells of primary tissue. On the basis of similar microfibrillar orientations between outer and inner wall lamellae, the cell walls ofCryptomeria parenchyma were judged to be predominantly secondary.Lignin was heterogeneously distributed in lamellate fashion and a high concentration characterized the thin middle lamella. Both types of parenchyma suggested a higher lignin content than adjacent longitudinal tracheids.     

Living Cells in Wood 3. Overview; Functional Anatomy of the Parenchyma Network

The very different evolutionary pathways of conifers and angiosperms are very informative precisely because their wood anatomy is so different. New information from anatomy, comparative wood physiology, and comparative ultrastructure can be combined to provide evidence for the role of axial and ray parenchyma in the two groups. Gnetales, which are essentially conifers with vessels, have evolved parallel to angiosperms and show us the value of multiseriate rays and axial parenchyma in a vessel-bearing wood. Gnetales also force us to re-examine optimum anatomical solutions to conduction in vesselless gymnosperms. Axial parenchyma in vessel-bearing woods has diversified to take prominent roles in storage of water and carbohydrates as well as maintenance of conduction in vessels. Axial parenchyma, along with other modifications, has superseded scalariform perforation plates as a safety mechanism and permitted angiosperms to succeed in more seasonal habitats. This diversification has required connection to rays, which have concomitantly become larger and more diverse, acting as pathways for photosynthate passage and storage. Modes of growth such as rapid flushing, vernal leafing-out, drought deciduousness and support of large leaf surfaces become possible, advantaging angiosperms over conifers in various ways. Prominent tracheid-ray pitting (conifers) and axial parenchyma/ray pitting to vessels (angiosperms) are evidence of release of photosynthates into conductive cells; in angiosperms, this system has permitted vessels to survive hydrologic stresses and function in more seasonal habitats. Flow in ray and axial parenchyma cells, suggested by greater length/width ratios of component cells, is confirmed by pitting on end walls of elongate cells: pits are greater in area, more densely placed, and are often bordered. Bordered pit areas and densities on living cells, like those on tracheids and vessels, represent maximal contact areas between cells while minimizing loss of wall strength. Storage cells in rays can be distinguished from flow cells by size and shape, by fewer and smaller pits and by contents. By lacking secondary walls, the entire surfaces of phloem ray and axial phloem parenchyma become conducting areas across which sugars can be translocated. The intercontinuous network of axial parenchyma and ray parenchyma in woods is confirmed; there are no “isolated” living cells in wood when three-dimensional studies are made. Water storage in living cells is reported anatomically and also in the form of percentile quantitative data which reveal degrees and kinds of succulence in angiosperm woods, and norms for “typically woody” species. The diversity in angiosperm axial and ray parenchyma is presented as a series of probable optimal solutions to diverse types of ecology, growth form, and physiology. The numerous homoplasies in these anatomical modes are seen as the informative results of natural experiments and should be considered as evidence along with experimental evidence. Elliptical shape of rays seems governed by mechanical considerations; unusually long (vertically) rays represent a tradeoff in favor of flexibility versus strength. Protracted juvenilism (paedomorphosis) features redirection of flow from horizontal to vertical by means of rays composed predominantly or wholly of upright cells, and the reasons for this anatomical strategy are sought. Protracted juvenilism, still little appreciated, occurs in a sizeable proportion of the world’s plants and is a major source of angiosperm diversification.     

Bordered pits in ray cells and axial parenchyma: the histology of conduction, storage, and strength in living wood cells

Bordered pits occur in walls of living ray cells of numerous species of woody dicotyledons. The occurrence of this feature has been minimally reported because the pits are relatively small and not easily observed in face view. Bordered pits are illustrated in sectional view with light microscopy and with scanning electron microscopy in face view for dicotyledonous and gnetalean woods. Bordered pits are more numerous and often have prominent borders on tangential walls of procumbent ray cells, but also occur on radial walls; they are approximately equally abundant on tangential and horizontal walls of upright cells, suggesting parallels to cell shape in flow pathway design. Axial parenchyma typically has secondary walls thinner than those of ray cells, but bordered pits or large simple pit areas occur on some cross walls of parenchyma strands. There is no apparent correlation between the phylogenetic position of species and the presence of borders in ray cells or axial parenchyma. Bordered pits represent a compromise between maximal mechanical strength and maximal conductive capability. High rates of flow of sugar solutions may occur if starch in ray cells or axial parenchyma is mobilized for sudden osmotic enhancement of the conductive stream or for rapid development of foliage, flowers, or fruits. Measurement of the secondary wall thickness of ray cells may offer simple inferential information about the role that rays play in the mechanical strength of woods. © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 153 , 157–168.     

What is disjunctive xylem parenchyma? A case study of the African tropical hardwood Okoubaka aubrevillei (Santalaceae)

The morphological variation and structure-function relationships of xylem parenchyma still remain open to discussion. We analyzed the three-dimensional structure of a poorly known type of xylem parenchyma with disjunctive walls in the tropical hardwood Okoubaka aubrevillei (Santalaceae). Disjunctive cells occurred among the apotracheal parenchyma cells and at connections between axial and ray parenchyma cells. The disjunctive cells were partly detached one from another, but their tubular structures connected them into a continuous network of axial and ray parenchyma. The connecting tubules had thick secondary walls and simple pits with plasmodesmata at the points where one cell contacted a tubule of another cell. The imperforate tracheary elements of the ground tissue were seven times longer than the axial parenchyma strands, a fact that supports a hypothesis that parenchyma cells develop disjunctive walls because they are pulled apart and partly separated during the intrusive growth of fibers. We discuss unresolved details of the formation of disjunctive cell walls and the possible biomechanical advantage of the wood with disjunctive parenchyma: the proportion of tissue that improves mechanical strength is increased by the intrusive elongation of fibers (thick-walled tracheids), whereas the symplastic continuum of the parenchyma is maintained through formation of disjunctive cells.     

WOOD ANATOMY AND RELATIONSHIPS OF LACTORIDACEAE

Mature wood of Lactoris, not previously available for study, reveals ten distinctive characters: vessels with simple perforation plates; vessels in pore multiples; vessel-to-axial parenchyma pits scalariform or transitional, vessel-to-vessel pits alternate; fiber-tracheids with vestigial pits; fiber-tracheids, vessels, and axial parenchyma storied; axial parenchyma vasicentric scanty; axial parenchyma either not subdivided or, if subdivided, with thin nonlignified walls between the cells (like the septa in septate fibers); rays wide and tall, little altered during ontogeny; ray cells upright; and ray cells taller adjacent to fascicular areas. All of these features occur in woods of Piper and other Piperaceae. The systematic position of Lactoris is therefore reassessed. Evidence available to date is consonant with placement of Lactoridaceae in Piperales, in which it would be more primitive than Piperaceae or Saururaceae. Features cited as evidence for alternative placements of Lactoridaceae are reviewed.     

Early ontogeny of vascular cambium III

Observations were made on structural changes from the procambium to cambium in the developing shoots ofRobinia pseudo-acacia andSyringa oblata, both of which are characterized by relatively short fusiform initials. In both species, the procambium in transverse view shows radial seriations of cells as a result of repeated tangential divisions, and there is an almost continuous procambial cylinder in the young stem in the earlier stage. The procambium in tangential view has initially a homogeneous structure and later develops into two systems, one made of long cells, the other of short cells. Some of the short cells elongate to intrude among neighbouring cells and some long cells divide radially as well as tangentially. InRobinia, long cells have transverse or tapering end walls at a relatively earlier stage and mainly tapering end walls in the subsequent stages. Although some of the short cells develop into long cells, the height of axial files of the short cells decreases only a little, because of subsequent transverse divisions and growth of cells. InSyringa, long cells have mainly transverse end walls at a relatively earlier stage and usually tapering end walls in the subsequent stages. Short cells in axial files have predominantly transverse end walls. A number of additional long cells are derived from elongating short cells in the later stages. Therefore, the height of axial files becomes apparently lower than that of earlier stages. Radial divisions in short cells occur to some extent. Results are discussed in relation to the structure of the vascular meristem inGinkgo, Aucuba, Weigela, and others.     

Wood Anatomy and the Development of Interxylary Phloem of Ipomoea hederifolia Linn. (Convolvulaceae)

In Ipomoea hederifolia Linn., stems increase in thickness by forming successive rings of cambia. With the increase in stem diameter, the first ring of cambium also gives rise to thin-walled parenchymatous islands along with thick-walled xylem derivatives to its inner side. The size of these islands increases (both radially and tangentially) gradually with the increase in stem diameter. In pencil-thick stems, that is, before the differentiation of a second ring of cambium, some of the parenchyma cells within these islands differentiate into interxylary phloem. Although all successive cambia forms secondary phloem continuously, simultaneous development of interxylary phloem was observed in the innermost successive ring of xylem. In the mature stems, thick-walled parenchyma cells formed at the beginning of secondary growth underwent dedifferentiation and led to the formation of phloem derivatives. Structurally, sieve tube elements showed both simple sieve plates on transverse to slightly oblique end walls and compound sieve plates on the oblique end walls with poorly developed lateral sieve areas. Isolated or groups of two to three sieve elements were noticed in the rays of secondary phloem. They possessed simple sieve plates with distinct companion cells at their corners. The length of these elements was more or less similar to that of ray parenchyma cells but their diameter was slightly less. Similarly, in the secondary xylem, perforated ray cells were noticed in the innermost xylem ring. They were larger than the adjacent ray cells and possessed oval to circular simple perforation plates. The structures of interxylary phloem, perforated ray cells, and ray sieve elements are described in detail.     

Early ontogeny of vascular cambium II.Aucuba japonica andWeigela coraeensis

InAucuba andWeigela the six vascular bundles distributed as a hexagon become connected tangentially by meristematic cells into a procambial cylinder in the early stage. In the tangential view, the procambial cylinder shows a rather homogeneous structure. InAucuba, some cells of the procambium elongate in a relatively earlier stage and the rest also elongate during subsequent stages. All of these cells have tapering end walls. Then some long cells divide transversely and form two systems in the vascular meristem, one made up of long cells and the other of short ones. The long cells become the fusiform initials and the short cells, the ray initials. InWeigela, the homogeneous procambium is organized in the later stages into two systems, one of long cells and the other of short cells in axial files. Most of the long cells have tapering end walls and the short cells transverse end walls. Some of the short cells elongate to intrude between adjacent cells and become long cells. The long cells become the fusiform initials. Radial divisions in some short cells occur occasionally. Some of these cells elongate and the rest remain in the axial files. Some short cells in the axial files are vertically separated from each other by the elongation of adjacent long cells. however, this occurs infrequently and the height of axial files is still several decades of cells. Short cells in axial files eventually become ray initials.     

Freezing behavior of xylem ray parenchyma cells in softwood species with differences in the organization of cell walls

Summary By cryo-scanning electron microscopy we examined the effects of the organization of the cell walls of xylem ray parenchyma cells on freezing behavior, namely, the capacity for supercooling and extracellular freezing, in various softwood species. Distinct differences in organization of the cell wall were associated with differences in freezing behavior. Xylem ray parenchyma cells with thin, unlignified primary walls in the entire region (all cells inSciadopitys verticillata and immature cells inPinus densiflora) or in most of the region (mature cells inP. densiflora and all cells inP. pariflora var.pentaphylla) responded to freezing conditions by extracellular freezing, whereas xylem ray parenchyma cells with thick, lignified primary walls (all cells inCrytomeria japonica) or secondary walls (all cells inLarix leptolepis) in most regions responded to freezing by supercooling. The freezing behavior of xylem ray parenchyma cells inL. leptolepis changed seasonally from supercooling in summer to extracellular freezing in winter, even though no detectable changes in the organization of cell walls were apparent. These results in the examined softwood species indicate that freezing behavior of xylem ray parenchyma cells changes in parallel not only with clear differences in the organization of cell walls but also with subtle sub-electron-microscopic differences, probably, in the structure of the cell wall.     

Systematic and phylogenetic value of wood anatomy in Heteromorpheae (Apiaceae,Apioideae)

The wood anatomy of all four woody genera of the tribe Heteromorpheae (Apiaceae, subfamily Apioideae) has been described and compared, based on 40 wood samples (representing nine species of Anginon, one species of Glia, three species of Heteromorpha and two species of Polemannia). The four genera were found to be relatively similar in their wood anatomy. Helical thickenings on the vessel walls occur in all species investigated and appear to represent an ancestral character state and a symplesiomorphy for the tribes Bupleurieae and Heteromorpheae. Each of four genera has a diagnostically different combination of character states relating to the diameter of vessels, size of intervessel pits, length of fibres, presence and arrangement of banded axial parenchyma, size of rays and ray cells, and presence of septate fibres and crystals in the ray cells. The occurrence of marginal axial parenchyma in Anginon and Glia may be an additional synapomorphy for these taxa. Variation in the wood anatomy of 31 samples from nine species of Anginon is not correlated with habitat (Fynbos or Succulent Karoo Biomes), but instead appears to reflect adaptations to seasonal aridity found in both ecosystems. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 158 , 569–583.     

Wood and bark anatomy of Gnetutn gnemon L.

Quantitative and qualitative data are presented for seven collections representing two varieties (unlike in habit) of Gnetum gnemon. Tracheids are present, but abundant and intermixed with them are septate fibre-tracheids rich in starch. Axial parenchyma has been reported only once previously for the species. Axial parenchyma is in strands of 4–10 cells, is rich in starch, is primarily vasicentric (paratracheal) in distribution, less commonly diffuse. About equally common are simple and compound perforation plates; the latter are composed of from two to about ten bordered foraminate perforations, the shape of which may be altered by crowding or coalescence, but is clearly still foraminate. Lateral walls of vessels bear pits that are vestured around pit cavities, not facing the pit membrane. Rays are composed mostly of procumbent cells; the tangential walls bear bordered pits. Crystals, present in ray cells and (rarely) axial parenchyma vary widely in size. Crystalliferous sclereids with layered walls, starch-rich parenchyma, and gelatinous secondary phloem fibres are the main components of bark. Early stages in origin of successive vascular cambia in bark are newly described. When representative conditions are derived from study of large numbers of slides, the classical view that Gnetum vessels are unlike those of angiosperms is supported. Features of Gnetum gnemon wood are discussed in the light of ecology and conductive physiology.     

Rearrangement of cells in storeyed cambium of<Emphasis Type="Italic"> Lonchocarpus sericeus</Emphasis> (Poir.) DC connected with formation of interlocked grain in the xylem

The history of cellular events in the storeyed cambium of Lonchocarpus sericeus (Poir.) DC was analysed on the basis of changes in the cell arrangement in successive layers and strata of axial parenchyma in the xylem. The mechanism of formation of the regular interlocked grain was investigated. Inclination of fusiform cells changes intensively whereas height and position of storeys in the successive layers of axial parenchyma are constant. As a result, new contacts between cells are formed by means of the intrusive growth of ends of cells belonging to one storey between the tangential walls of cells of the neighbouring storey and unequal periclinal divisions, which give a new shape to the initials. The concept of intrusive growth between the radial walls of the fusiform initials in the formation of xylem with interlocked grain should be revised on this basis.     

Immunohistochemical localization of agatharesinol,a heartwood norlignan,in Cryptomeria japonica

Localization of a heartwood norlignan, agatharesinol, in Sugi (Japanese cedar, Cryptomeria japonica D. Don, Taxodiaceae) was investigated by immunohistochemistry. Immuno light microscopy showed that the contents of ray parenchyma cells were immunostained in heartwood but not in sapwood. The staining of the heartwood tissue was competitively inhibited by agatharesinol but not by other Sugi heartwood extractives, and was, furthermore, markedly reduced by pre-extraction of the tissue with MeOH. These results indicated that the staining can be ascribed to the immunolabeling of agatharesinol in situ. The accumulations over the inner surface of some tracheid cell walls adjacent to the ray parenchyma cells were also immunolabeled, while the contents in axial parenchyma cells were not. In conclusion, agatharesinol was localized in the ray parenchyma cells in Sugi heartwood, and differences between the chemical structure of the contents of ray and axial parenchyma cells were also suggested.     

Ontogeny of the interfascicular cambium in the petiole ofTabebuia rosea DC. (Bignoniaceae)

In order to elucidate the origin of interfascicular cambium in the petiole ofTabebuia rosea, transverse and tangential views of the cells in the interfascicular region during the different developmental stages of the petiole have been traced. Interfascicular cambium originates from the interfascicular parenchyma, which has been differentiated from interfascicular vascular meristem cells. Interfascicular parenchyma cells divide periclinally differentiating into the interfascicular metacambial cells and then into the cambium. Tangentially the homogenous structure of interfascicular parenchyma cells in the early stage gradually changes into a heterogenous structure with long and short cells from which fusiform and ray initials are derived, respectively. Ontogenetic pattern of the interfascicular cambium is similar to that of the fascicular one with interfascicular metacambium as an intermediate stage.     

Two Fossil Woods from Heilongjiang Sheng of China

Two fossil coniferous woods, Xenoxylon latiporosum (Cramer) Gothan and Protopiceoxylon amurense sp. nov. found in Heilongjiang Sheng of China are described in this paper. The diagnosis of Protopiceoxylon amurense sp. nov. is as follows: Growth rings distinct. The transition from the early wood to the late wood slightly abrupt. Tracheids of the early wood square to rectangular in the transverse section. Bordered pits on the radial walls of early wood traeheids 1-2-seriate, opposite, circular with round apertures. The erassula well marked. Walls of the late wood traeheids much thickened. Rays uniseriate and partly biseriate, 1–45 cells high. The highness of the biseriate part is often more than 2/3 that of the ray. Transverse walls of ray cells rather densely pitted and the tangential walls with marked nodular thickenings. The pitting of the cross-field is small, simple or taxodioid type. The axial wood parenchyma absent. The axial resin canal, both traumatic and normal, present, separate or gathered in tangential rows. Epithelial cells with thickwalls are more than 10 in number. The affinities of the two woods are discussed. The age of the fossil woods is assigned to Late Jurassic to Early Cretaceous. It is inferred that they grew in the then north subtropical warm temperate zone and on a hilly area with an elevation of 1000 metres approximately.