Inhibition of phenylalanine ammonia-lyase activity causes the depression of lignin accumulation of secondary wall thickening in isolatedZinnia mesophyll cells

Summary Isolated mesophyll cells ofZinnia elegans L. cv. Canary Bird differentiate into tracheary elements in differentiation (D) medium. These elements develop lignified secondary wall thickenings. The influence of 2-aminoindan-2-phosphonic acid (AIP), an inhibitor of phenylalanine ammonia-lyase (PAL), on lignification ofZinnia tracheary elements was examined. The mesophyll cells were cultured in D and AIP media. The latter medium, in which 100 M AIP was added to the D medium, inhibited PAL activity, though the differentiation proceeded. Morphological differences of secondary wall thickenings cultured in these two types of media were investigated under an UV microscope and a transmission electron microscope. The secondary wall thickenings at 96 h in the D medium showed strong UV absorption. The fibrillar structure of the thickenings observed clearly at 72 h was covered with electron opaque materials by 96 h. The secondary wall thickenings at 96 h in the AIP medium showed weak UV absorption. The thickenings at 96 h had a cracked appearance. Furthermore, the thickenings showed a little irregular or wavy arrangement of cellulose microfibrils and had many pores and spaces between microfibrils. From these results, the role of lignin accumulation in the formation of secondary wall thickenings was discussed.Abbreviations AIP 2-aminoindan-2-phosphonic acid - PAL phenylalanine ammonia-lyase     

Immunocytochemical Localization of Phenylalanine Ammonia-Lyase and Cinnamyl Alcohol Dehydrogenase in Differentiating Tracheary Elements Derived from Zinnia Mesophyll Cells

Secondary wall thickening is the most characteristic morphologicalfeature of the differentiation of tracheary elements. Isolatedmesophyll cells of Zinnia elegans L. cv. Canary Bird in differentiationmedium are converted to tracheary elements, which develop lignifiedsecondary wall thickenings. Using this system, we investigatedthe distribution of two enzymes, phenylalanine ammonia-Iyase(PAL) (EC 4.3.1.5 [EC] ) and cinnamyl alcohol dehydrogenase (CAD)(EC 1.1.1.195 [EC] ), by both biochemical and immunological methods.Both PAL and CAD appear to be key enzymes in the biosynthesisof lignin precursors, and they have been shown to be associatedwith the differentiation of tracheary elements. Cultured cellswere collected after various times in culture. The culture mediumwas separated from cells by centrifugation and designated fraction(1), the extracellular fraction. The collected cells were homogenizedand separated into four fractions: (2) cytosol; (3) microsomes;(4) cell walls (loosely bound material); and (5) cell walls(tightly bound material). PAL activity was detected in eachfraction. The extracellular fraction consistently had the greatestPAL activity. Moreover, PAL activity in the cytosolic fractionincreased rapidly prior to lignification, as it did in boththe microsomal and the cell wall (tightly bound) fractions duringlignification. Antisera against PAL and against CAD detectedthe proteins with molecular masses that corresponded to thoseof PAL and CAD in Zinnia. Immuno-electron microscopy revealedthat, in differentiating tracheary elements, PAL was dispersedin the cytoplasmic matrix and was located on Golgi-derived vesiclesand on the secondary wall thickenings. "Cell-free" immuno-lightmicroscopy supported the putative distribution of PAL on lignifyingsecondary walls. The pattern of distribution of CAD was similarto that of PAL. Thus, both PAL and CAD seemed to be localizedin secondary wall thickenings. From the results of both biochemicalassays and immunocytochemical staining, it appeared that atleast two types of PAL and CAD are present in differentiatingcells. One type of each enzyme is distributed in the cytosol,while the other is secreted from the Golgi apparatus and transportedby Golgi-derived vesicles to the secondary wall thickenings. (Received April 19, 1996; Accepted November 18, 1996)     

Sucrose synthase localizes to cellulose synthesis sites in tracheary elements.

The synthesis of crystalline cellulose microfibrils in plants is a highly coordinated process that occurs at the interface of the cortex, plasma membrane, and cell wall. There is evidence that cellulose biogenesis is facilitated by the interaction of several proteins, but the details are just beginning to be understood. In particular, sucrose synthase, microtubules, and actin have been proposed to possibly associate with cellulose synthases (microfibril terminal complexes) in the plasma membrane. Differentiating tracheary elements of Zinnia elegans L. were used as a model system to determine the localization of sucrose synthase and actin in relation to the plasma membrane and its underlying microtubules during the deposition of patterned, cellulose-rich secondary walls. Cortical actin occurs with similar density both between and under secondary wall thickenings. In contrast, sucrose synthase is highly enriched near the plasma membrane and the microtubules under the secondary wall thickenings. Both actin and sucrose synthase lie closer to the plasma membrane than the microtubules. These results show that the preferential localization of sucrose synthase at sites of high-rate cellulose synthesis can be generalized beyond cotton fibers, and they establish a spatial context for further work on a multi-protein complex that may facilitate secondary wall cellulose synthesis.     

The role of microtubules in vessel member differentiation inColeus

Summary The role of microtubules in tracheary element formation in cultured stem segments ofColeus has been investigated through the use of the antimicrotubule drug, colchicine. Colchicine treatment of the cultured stem segments produced a dual effect on xylem differentiation. If applied at the time of stem segment isolation or shortly thereafter, wound vessel member formation is almost completely blocked. However, if colchicine is applied after the third day of culture, it does not inhibit differentiation, but instead large numbers of xylem elements are formed which have highly deformed secondary walls. Both effects are related to colchicine's specific affinity for microtubules. In the first case it is shown that colchicine blocks mitosis, presumably by destroying the spindle apparatus, and thus inhibits divisions which are prerequisite for the initiation of xylem differentiation. While, if colchicine is applied after the necessary preparative divisions have taken place, it destroys specifically the cortical microtubules associated with the developing bands of secondary wall, thus causing aberrant wall deposition.Light and electron microscopic analysis of drug-treated cells reveals that the secondary wall becomes smeared over the surface of the primary wall and does not retain the discrete banded pattern characteristic of secondary thickenings in untreated cells. Examination of colchicine-treated secondary walls in KMnO₄ fixed material shows that in the absence of microtubules the cellulose microfibrils lose their normal parallel orientation and are deposited in swirls and curved configurations, and often lie at sharp angles to the axis of the secondary wall band. Microtubules, thus, appear to play a major role in defining the pattern of secondary wall deposition and in directing the orientation of the cellulose microfibrils of the wall. Factors in addition to microtubules also act in controlling the secondary wall pattern, since we observe that even in the absence of microtubules secondary thickenings of two adjacent xylem elements are deposited directly opposite one another across the common primary wall.     

Changes in Cell Wall Architecture of Differentiating Tracheids of Pinus thunbergii during Lignification

The cell wall architecture, before and after lignification,of differentiating tracheids in Pinus thunbergii has been examinedusing a rapid-freeze deep-etching technique combined with transmissionelectron microscopy. Replicas of cells from the cambial zoneshowed that the unlignified primary cell wall was highly porouswith microfibrils extensively interconnected by crosslinks.The unlignified secondary cell wall has unidirectional microfibrils,more or less associated in bundles, forming a wavy pattern aroundpores of characteristic slit-like shape with narrowing ends.As the lignification progresses, the cell wall structure becomesdense, with no detectable pores. Delignification of wood samplesleads to the reappearance of crosslinks, individual microfibrilsand pores in the secondary cell wall, although in a somewhataltered shape. In addition, cellulose-synthesizing enzyme complexes(rosettes) have for the first time been detected on the plasmamembrane of differentiating xylem cells of softwood. (Received August 28, 1998; Accepted March 10, 1999)     

Developmental Features of Cell Wall Formation in Sieve Elements of the Grass Aegilops comosa var. thessalica

In differentiating sieve elements of Aegilops comosa var. thessalicadictyosomes are abundant and they produce numerous smooth vesicles.Coated vesicles seem to bud from smooth ones. Since both kindsof vesicles appear both in the cytoplasm and in associationwith the plasmalemma, it is proposed that they move to and fusewith the plasmalemma transferring products for cell wall synthesis.During differentiation sub-plasmalemmal microtubules are initiallyscarce and randomly oriented but soon afterwards they becomenumerous and transversely oriented to the long axis. Cellulosemicrofibrils in the cell wall appear to run parallel to themicrotubules and the latter may regulate microfibril orientation. Root protophloem sieve elements develop wave-like wall thickenings,which are, during development, overlaid by microtubules perpendicularto the long axis. Just after maturation these thickenings progressivelybecome smooth and finally the walls appear uniform in thickness.The wave-like wall thickenings may function as stored wall material,utilized in later stages of development when wall material willbe needed and its synthesis will be impossible because of theabsence of a synthesizing mechanism in the highly degraded protoplastsof mature sieve elements. It is suggested that in this way thethickenings may enable root protophloem sieve elements to growand keep pace with the active clongation of the surroundingcells. Aegilops comosa var. thessalica, sieve elements. cell wall, microtubules, dictyosomes, coated vesicles, wave-like thickenings     

Aspects of Cell Wall Structure and the Development of the Velamen in Ansellia gigantea Reichb. f.

A transmission and scanning electron microscope study was madeof cell wall development in the root velamen of Ansellia gigantea.The pattern of fibrillar deposition in the primary walls wasestablished by means of shadowed surface preparations. The helicalwall thickenings were shown to originate by the localised appositionof bundles of orientated 20–30 nm cellulose fibrils. Thisproceeds from near the tips of the radially elongated cells.Although microtubules were associated with later stages of helixdeposition, there was no evidence for cytoplasmic pre-patteming.The large wall perforations, circumscribed by secondary walldepositions, develop at the sites of pit fields. The implicationsof the present observations are discussed, particularly as theyappear to relate to general principle of wall development intracheary elements.     

Microfibril orientation in differentiating and maturing fibre and parenchyma cell walls in culms of bamboo (Phyllostachys viridi-glaucescens (Garr.) Riv. & Riv.)

Results of trials using chemical and enzymatic wall extractants for the removal of matrix materials for in situ observations of newly deposited microfibrils are described. Observations were then made of the orientation of microfibrils on the inner walls of differentiating and maturing fibres and parenchyma cells under the FESEM. Orientation changes were similar in both cell types. During very early primary wall development, deposition of microfibrils was in more or less axial alignment, which was later superseded by microfibrils in transverse orientation (90^o to the long axis). A transverse orientation of microfibrils remained throughout much of primary wall synthesis, until an abrupt shift occurred to a sloped orientation during late primary wall synthesis. Microfibrils of the first secondary wall layer were in axial alignment or steeply sloped. In subsequent secondary wall deposition there was an alternation between a transverse and a sloped or axial alignment in maturing fibres and parenchyma cells.     

THE FINE STRUCTURE OF DIFFERENTIATING XYLEM ELEMENTS

Differentiating xylem elements of Avena coleoptiles have been examined by light and electron microscopy. Fixation in 2 per cent phosphate-buffered osmium tetroxide and in 6 per cent glutaraldehyde, followed by 2 per cent osmium tetroxide, revealed details of the cell wall and cytoplasmic fine structure. The localized secondary wall thickening identified the xylem elements and indicated their state of differentiation. These differentiating xylem elements have dense cytoplasmic contents in which the dictyosomes and elements of rough endoplasmic reticulum are especially numerous. Vesicles are associated with the dictyosomes and are found throughout the cytoplasm. In many cases, these vesicles have electron-opaque contents. "Microtubules" are abundant in the peripheral cytoplasm and are always associated with the secondary wall thickenings. These microtubules are oriented in a direction parallel to the microfibrillar direction of the thickenings. Other tubules are frequently found between the cell wall and the plasma membrane. Our results support the view that the morphological association of the "microtubules" with developing cell wall thickenings may have a functional significance, especially with respect to the orientation of the microfibrils. Dictyosomes and endoplasmic reticulum may have a function in some way connected with the synthetic mechanism of cell wall deposition.     

The development and ultrastructure of the testa and tracheid bar inErythrina lysistemon Hutch. (Leguminosae: Papilionoideae)

Summary The development of the testa was studied inErythrina lysistemon using both light and electron microscopy. Cells of the outer epidermis of the outer integument divide anticlinally and undergo radial elongation to form a palisade layer. The outer tangential walls are thickened at an early stage, and deposition of fluted thickenings on the radial walls occurs at maturity. Palisade cells in the hilar region differentiate from sub-funicular tissue, and at maturity the outer ends of the cells undergo extensive deposition of secondary walls and associated lignification. The light line occurs at the junction between the outer, thickened portions of the cells and the inner, less thickened portions. An electron-translucent (suberised) cap develops in the outer tangential walls of the palisade cells at a late stage. Microtubules and dictyosomes are closely associated with the developing thickenings in palisade and tracheid bar, and the microtubules run parallel to the wall microfibrils. Differentiation of the tracheid bar coincides with final secondary wall deposition and lignification in the hilar palisade. The cells of the tracheid bar are dead at maturity, but are surrounded by sheaths of elongate parenchyma.     

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.     

Structural cell-wall proteins in protoxylem development: evidence for a repair process mediated by a glycine-rich protein

Polyclonal antibodies were used to localize structural cell-wall proteins in differentiating protoxylem elements in etiolated bean and soybean hypocotyls at the light- and electron-microscopic level. A proline-rich protein was localized in the lignified secondary walls, but not in the primary walls of protoxylem elements, which remain unlignified, as shown with lignin-specific antibodies. Secretion of the proline-rich protein was observed during lignification in different cell types. A glycine-rich protein (GRP1.8) was specifically localized in the modified primary walls of mature protoxylem elements and in cell corners between xylem elements and xylem parenchyma cells. The protein was secreted by Golgi bodies both in protoxylem cells after the lignification of their secondary walls and in the surrounding xylem parenchyma cells. The modified primary walls of protoxylem elements were visualized under the light microscope as filaments or sheets staining distinctly with the protein stain Coomassie blue. Electron micrographs of these walls show that they are composed of an amorphous material of moderate electron-density and of polysaccharide microfibrils. These materials form a three-dimensional network, interconnecting the ring- or spiral-shaped secondary wall thickenings of protoxylem elements and xylem parenchyma cells. The results demonstrate that the modified primary walls of protoxylem cells are not simply breakdown products due to partial hydrolysis and passive elongation, as believed until now. Extensive repair processes produce cell walls with unique staining properties. It is concluded that these walls are unusually rich in protein and therefore have special chemical and physical properties.     

The Net Orientation of Wall Microfibrils in the Outer Periclinal Epidermal Walls of Seedling Leaves of Wheat

Use of the dichroic stain chlor-zinc-iodine revealed that thenet orientation of cellulose wall microfibrils in the outerparadermal wall of the epidermis of seedling wheat leaves isprincipally transverse in the extension zone. The net orientationof microfibrils changes abruptly to principally longitudinalat the end of cell elongation. The net angle of orientationof microfibrils in the extension zone was not a function ofRht-dosage (number of dwarfing alleles), and neither leaf extensionrate nor estimated maximum relative elemental rate of elongationwere functions of microfibril orientation. The results indicatethat elongation rates are not regulated by the net angle oforientation of microfibrils and support the concept that leafextension rate is regulated by the length of the extension zone.Copyright1995, 1999 Academic Press Cellulose wall microfibrils, extension zone, elongation, Rht, wheat, Triticum aestivum L     

Observations on the Fine Structure of Plant Cell Walls II. The Microfibrillar Framework of the Parenchymatous Cell Wall in Cucurbita

The microfibrillar framework of parenchymatous walls in Cucurbitawas observed in petioles treated so as to remove various non-cellulosiccell wall components. Such extraction typically results in separationof the microfibrillar components into concentric lamellae. Thenumber and thickness of these lamellae vary according to theage and type of cell wall. The microfibrils appear to be orientatedwithin the plane of their lamellae but the orientation may varyin successive lamellae, and in many walls the crossed polylamellatecondition was detected. The collenchyma—and the outerepidermal cell walls show an alternation of lamellae with almostvertical microfibrils with those with a practically transverseorientation. In ordinary parenchymatous walls the alternationis not so extreme and is revealed only by the occasional presenceof the ‘herring bone pattern’ in non-radial sections.As a rule the lamellae are continuous around the circumferenceof a cell though individual lamellae may vary in thickness andsometimes appear to ‘fade out’. The present observationssuggest that growth of the primary wall occurs by depositionof microfibrils in successive lamellae thus confirming the basicpremise of the multinet theory of growth.     

Arrangement of Cellulose Microfibrils in Walls of Elongating Parenchyma Cells

The arrangement of cellulose microfibrils in walls of elongating parenchyma cells of Avena coleoptiles, onion roots, and celery petioles was studied in polarizing and electron microscopes by examining whole cell walls and sections. Walls of these cells consist firstly of regions containing the primary pit fields and composed of microfibrils oriented predominantly transversely. The transverse microfibrils show a progressive disorientation from the inside to the outside of the wall which is consistent with the multinet model of wall growth. Between the pit-field regions and running the length of the cells are ribs composed of longitudinally oriented microfibrils. Two types of rib have been found at all stages of cell elongation. In some regions, the wall appears to consist entirely of longitudinal microfibrils so that the rib forms an integral part of the wall. At the edges of such ribs the microfibrils can be seen to change direction from longitudinal in the rib to transverse in the pit-field region. Often, however, the rib appears to consist of an extra separate layer of longitudinal microfibrils outside a continuous wall of transverse microfibrils. These ribs are quite distinct from secondary wall, which consists of longitudinal microfibrils deposited within the primary wall after elongation has ceased. It is evident that the arrangement of cellulose microfibrils in a primary wall can be complex and is probably an expression of specific cellular differentiation.     

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.     

Modification in Cell Shape Unrelated to Cellulose Microfibril Orientation in Growing Thallus Cells of Chaetomorpha moniligera

Cellulose microfibril orientation patterns in thallus cellsof Chaetomorpha moniligera were studied, and the relationshipbetween the microfibril and the peripheral microtubule arrangementsduring cell-shape modification by colchicine was examined. Inthe cuttings from growing thalli, linearly arranged cylindricalcells developed into cask-shaped cells during 4–6 daysof culture at 27?C. In the cylindrical cells, microfibrils formingthe innermost portion of the wall were arranged alternatelyin longitudinal and transverse directions, but peripheral microtubuleswere always arranged only in a longitudinal direction. Thesefeatures were also noted in the cask-shaped cells. Colchicineat 10^–3M and 3?10^–3M accelerated both cell expansionand wall thickening with matrix deposition, but the directionsin which both microfibrils and microtubules were arranged werethe same as those of the cylindrical cells. These results indicatethat (1) the microfibril and microtubule arrangements of Chaetomorphaare not necessarily correlated, (2) changes in cell shape ofChaetomorpha are not necessarily accompanied by changes in thearrangement of cell-wall microfibrils, and (3) colchicine playsa role in the loosening and thickening of cell walls by enhancingmatrix deposition. (Received June 2, 1986; Accepted February 13, 1987)     

LIGNIFICATION DURING SECONDARY WALL FORMATION IN COLEUS: AN ELECTRON MICROSCOPIC STUDY

The fine structure of lignin deposition was examined in developing secondary walls of wound vessel members in Coleus. KMnO₄, which was used as the fixative, selectively reacts with the lignin component of the cell wall and thus can be used as a highly sensitive electron stain to follow the course of lignification during secondary wall deposition. Lignin was first detected as conspicuuos electron-opaque granules in the primary wall in the region where the secondary wall thickening arises and as fine granular striations extending into the very young secondary wall. As the secondary wall develops lignification becomes progressively more extensive. In cross sections the lignified secondary wall appears as concentric, fine granular striations; in tangent al or oblique sections it is seen as delicate, beaded fibrils paralleling the long axis of the thickening. High magnification of tangential or oblique sections shows that the fibrillar appearance is due to the presence of alternating light and dark layers each approximately 25-35 A wide. It is assumed that the light layers are the cellulose microfibrils and the dark regions contain lignin which fills the space between the microfibrils. KMnO₄, by selectively reacting with lignin, thus negatively stains the cellulose microfibrils revealing their orientation and dimensions.     

Roles of microtubules and cellulose microfibril assembly in the localization of secondary-cell-wall deposition in developing tracheary elements

Summary. The roles of cellulose microfibrils and cortical microtubules in establishing and maintaining the pattern of secondary-cell-wall deposition in tracheary elements were investigated with direct dyes to inhibit cellulose microfibril assembly and amiprophosmethyl to inhibit microtubule polymerization. When direct dyes were added to xylogenic cultures of Zinnia elegans L. mesophyll cells just before the onset of differentiation, the secondary cell wall was initially secreted as bands composed of discrete masses of stained material, consistent with immobilized sites of cellulose synthesis. The masses coalesced, forming truncated, sinuous or smeared thickenings, as secondary cell wall deposition continued. The absence of ordered cellulose microfibrils was confirmed by polarization microscopy and a lack of fluorescence dichroism as determined by laser scanning microscopy. Indirect immunofluorescence showed that cortical microtubules initially subtended the masses of dye-altered secondary cell wall material but soon became disorganized and disappeared. Although most of the secondary cell wall was deposited in the absence of subtending cortical microtubules in dye-treated cells, secretion remained confined to discrete regions of the plasma membrane. Examination of non-dye-treated cultures following application of microtubule inhibitors during various stages of secondary-cell-wall deposition revealed that the pattern became fixed at an early stage such that deposition remained localized in the absence of cortical microtubules. These observations indicate that cortical microtubules are required to establish, but not to maintain, patterned secondary-cell-wall deposition. Furthermore, cellulose microfibrils play a role in maintaining microtubule arrays and the integrity of the secondary-cell-wall bands during deposition.Correspondence and reprints: Department of Biological Sciences, University of Rhode Island, Kingston, RI 02881, U.S.A.Present address: Biology Editors Co., Peacedale, Rhode Island, U.S.A.Present address: Department of Biology and Marine Biology, Roger Williams University, Bristol, Rhode Island, U.S.A.Present address: Department of Crop Science and Department of Botany, North Carolina State University, Raleigh, North Carolina, U.S.A.     

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。