Stem anatomy of Dolichos lablab Linn (Fabaceae): Origin of cambium and reverse orientation of vascular bundles

Secondary growth in the stem of Dolichos lablab is achieved by the formation of eccentric successive rings of vascular bundles. The stem is composed of parenchymatous ground tissue and xylem and phloem confined to portions of small cambial segments. However, development of new cambial segments can be observed from the obliterating ray parenchyma, the outermost phloem parenchyma and the secondary cortical parenchyma. Initially cambium develops as small segments, which latter become joined to form a complete cylinder of vascular cambium. Each cambial ring is functionally divided into two distinct regions. The one segment of cambium produces thick-walled lignified xylem derivatives in centripetal direction and phloem elements centrifugally. The other segment produces only thin-walled parenchyma on both xylem and phloem side. In mature stems, some of the axial parenchyma embedded deep inside the xylem acquires meristematic activity and leads to the formation of thick-walled xylem derivatives centrifugally and phloem elements centripetally. The secondary xylem comprises vessel elements, tracheids, fibres and axial parenchyma. Rays are uni-multiseriate in the region of cambium that produces xylem and phloem derivatives, while in some of the regions of cambium large multiseriate, compound, aggregate and polycentric rays can be noticed.     

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.     

SUCCESSIVE CAMBIA IN THE STEM OF PHYTOLACCA DIOICA

Phytolacca dioica L., an evergreen tree of the Phytolaccaceae, is one of the species of Phytolacca which shows anomalous secondary thickening in its stem. This mode of thickening has been regarded as successive cambial activity or alternatively, in some more recent interpretations, as thickening by unidirectional activity of a cambial zone. The stem thickening of P. dioica is of the former type. The cambium produces fascicular strands, showing centrifugal differentiation of xylem and centripetal differentiation of phloem on opposite sides of the cambial layer, and rays are produced between the fascicular areas. In both xylem and phloem the younger elements are closer to the cambium than the older elements. Succeeding cambia arise periodically by periclinal divisions in a layer of parenchyma cells two or three cells beyond the outermost intact phloem derived from the current cambium. Each cambium forms a few parenchyma cells on both sides before it forms derivatives which mature into lignified xylem elements or conductive elements of the phloem. The parenchyma thus formed toward the outside later becomes the site of the origin of the succeeding cambium. Only one or two layers of this phloem parenchyma go on to form the new cambium; the remaining cells accumulate between the outermost phloem and the cortex. P. weberbaueri shows stem structure similar to P. dioica. P. meziana, a shrub, shows normal stem structure.     

Stem anatomy and development of successive cambia in Hebanthe eriantha (Poir.) Pedersen: a neotropical climbing species of the Amaranthaceae

Hebanthe eriantha (Poir.) Pedersen, a climbing species of the Amaranthaceae increases in stem thickness by forming successive cambia. The family is dominated by herbaceous species and is constantly under discussion due to its disputed nature of the meristem. In the young stem small alternate segments of vascular cambium cease to divide and new arc of cambium initiates outside to it. The newly formed arcs connect with pre-existing alternate segments of cambium to complete the ring. On the contrary, in thick stems, instead of small segments, complete ring of cambium is replaced by new one. These new alternate segments/cambia originate from the parenchyma cells located outside to the phloem produced by previous cambium. Cambium is storied and exclusively composed of fusiform initials while ray cells remain absent at least in the early part of the secondary growth. However, large heterocellular rays are observed in 15-mm diameter stems but their frequency is much lower. In some of the rays, ray cells become meristematic and differentiate into radially arranged xylem and phloem elements. In fully grown plants, stems are composed of several successive rings of secondary xylem alternating with secondary phloem. Secondary xylem is diffuse-porous and composed of vessels, fibres, axial parenchyma while exceptionally large rays are observed only in the outermost regions of thick stems. Vessel diameter increases progressively from the centre towards the periphery of stems. Although the origin of successive cambia and composition of secondary xylem of H. eriantha remains similar to other herbaceous members of Amaranthaceae, the occurrence of relatively wider and thick-walled vessels and large rays in fully grown plants is characteristic to climbing habit.     

白鲜营养器官解剖结构及其与白鲜碱的积累关系

应用植物解剖学、组织化学及植物化学方法对白鲜营养器官根、茎、叶的结构及其生物碱的积累进行了研究。结果显示:(1)白鲜根的次生结构以及茎和叶的结构类似一般双子叶植物;白鲜多年生根主要由周皮、次生韧皮部、维管形成层以及次生木质部组成,根次生韧皮部中可见大量的淀粉、草酸钙簇晶、韧皮纤维以及油细胞;茎由表皮、皮层、维管组织和髓组成;叶由表皮、栅栏组织、海绵组织和叶脉组成;在茎和叶初生韧皮部的位置均分布有韧皮纤维,在叶表皮上分布有头状腺毛和非腺毛;在茎和叶紧贴表皮处分布有分泌囊。(2)组织化学分析结果显示:在白鲜多年生根中,生物碱类物质主要分布在周皮、次生韧皮部、维管形成层和木薄壁细胞中;在茎中,生物碱主要分布在表皮、皮层、韧皮部、木薄壁细胞及髓周围薄壁细胞中;在叶中,生物碱主要分布在表皮细胞、叶肉组织和维管组织的薄壁细胞;此外在分泌囊和头状腺毛中亦含有生物碱类物质。(3)植物化学结果显示,秦岭产白鲜根皮/白鲜皮、根木质部、茎和叶中白鲜碱含量分别为0.041%、0.012%、0.004%和0.002%,其中木质部中白鲜碱含量和其他部分地区白鲜皮中白鲜碱含量类似。研究表明,在秦岭产白鲜营养器官中,除根皮/白鲜皮外,在根木质部亦含有大量的白鲜碱,且在茎和叶中亦含有一定的白鲜碱,具有潜在的开发利用价值。     

绞股蓝营养器官的结构及其人参皂甙的组织化学定位研究

绞股蓝是多年生草质藤本植物。根系由不定根组成,根的初生结构木质部为2－4原型,次生结构中栓内层较厚,攀缘茎,具5棱,周围纤维连成一环,幼茎的维管束排成两圈,外圈5个,内圈4或5个,老茎圆柱形,周围纤维呈不连续环状,维管束具次生木质部和次生韧皮部,排成一圈,掌状复叶互生,小叶5－7片,背腹型,叶柄具5束维管束,进入小叶时分为7－9束,茎和叶的初生维管束为双韧维管束,组织化学实验表明,绞股蓝人参皂甙主要分布在营养器官的同化组织及韧皮部薄壁细胞中,厚角组织,表皮及周皮的栓内层也有少量分布。     

六盘山鸡爪大黄根蒽醌类化合物组织化学定位的研究

采用组织化学方法研究了六盘山鸡爪大黄根蒽醌类化合物的组织化学定位特征及贮藏和积累的规律。结果表明：蒽醌类化合物在根内的贮藏是多位点的,在根周皮的木栓层和栓内层、次生维管组织的维管射线和根中央的部分木薄壁细胞内不同程度地贮藏和积累了一定数量的蒽醌类化合物,次生木质部的木射线和次生韧皮部的韧皮射线是主要贮藏和积累的部位,早期形成的维管射线中蒽醌类化合物的含量较晚期形成的射线含量高。     

STRUCTURALLY PRESERVED FOSSIL PLANTS FROM ANTARCTICA. I. ANTARCTICYCAS,GEN. NOV., A TRIASSIC CYCAD STEM FROM THE BEARDMORE GLACIER AREA

Silicified stems with typical cycadalean anatomy are described from specimens collected from the Fremouw Formation (Triassic) in the Transantarctic Mountains of Antarctica. Axes are slender with a large parenchymatous pith and cortex separated by a narrow ring of vascular tissue. Mucilage canals are present in both pith and cortex. Vascular tissue consists of endarch primary xylem, a narrow band of secondary xylem tracheids, cambial zone, and region of secondary phloem. Vascular bundles contain uni- to triseriate rays with larger rays up to 2 mm wide separating the individual bundles. Pitting on primary xylem elements ranges from helical to scalariform; secondary xylem tracheids exhibit alternate circular bordered pits. Traces, often accompanied by a mucilage canal, extend out through the large rays into the cortex where some assume a girdling configuration. A zone of periderm is present at the periphery of the stem. Large and small roots are attached to the stem and are conspicuous in the surrounding matrix. The anatomy of the Antarctic cycad is compared with that of other fossil and extant cycadalean stems.     

Stem anatomy of the dwarf subshrub Cressa cretica L. (Convolvulaceae)

Stem anatomy and development of medullary phloem are studied in the dwarf subshrub Cressa cretica L. (Convolvulaceae). The family Convolvulaceae is dominated by vines or woody climbers, which are characterized by the presence of successive cambia, medullary- and included phloem, internal cambium and presence of fibriform vessels. The main stems of the not winding C. cretica shows presence of medullary (internal) phloem, internal cambium and fibriform vessels, whereas successive cambia and included phloem are lacking. However, presence of fibriform vessels is an unique feature which so far has been reported only in climbing members of the family. Medullary phloem develops from peri-medullary cells after the initiation of secondary growth and completely occupies the pith region in fully grown mature plants. In young stems, the cortex is wide and formed of radial files of tightly packed small and large cells without intercellular air spaces. In thick stems, cortical cells become compressed due to the pressure developed by the radial expansion of secondary xylem, a feature actually common to halophytes. The stem diameter increases by the activity of a single ring of vascular cambium. The secondary xylem is composed of vessels (both wide and fibriform), fibres, axial parenchyma cells and uni-seriate rays. The secondary phloem consists of sieve elements, companion cells, axial and ray parenchyma cells. In consequence, Cressa shares anatomical characteristics of both climbing and non-climbing members. The structure of the secondary xylem is correlated with the habit and comparable with that of other climbing members of Convolvulaceae.     

Microfilament bundles in the roots of a conifer,Chamaecyparis obtusa

Summary The distribution of microfilament bundles (MFBs) in the primary tissues ofChamaecyparis obtusa roots has been investigated by electron microscopy. Nomarski differential interference-contrast (NDIC) images of MFBs in sections of embedded materials are also presented to complement the ultrastructural observations. The peripheral phloem parenchyma cells, also known as precursory phloem, generally possess greater numbers of MFBs than do any other cell type. MFBs are apparently absent in the cortical, meristematic or root cap tissues. The number of MFBs seen in a transection of a cell varies according to its position in the ontogenetic sequence. While all the MFBs in peripheral phloem parenchyma cells lie within 2.0 m from and on occasion contact the plasmamembrane, some MFBs in other phloem and xylem cells are located in the central areas of the cytoplasm. The possible three-dimensional distribution of MFBs in a streaming peripheral phlowm parenchyma cell is discussed.     

The Structure Anomalous Secondary Growth of Stem in Gnetum montanum

In the stem of Gnetnm montanum Mgr. the general arrangement of various tissues and its pattern of secondary growth are very similar to those of angiosperms. The most conspicuous similarity lies in that the xylem contains vessels and the phloem, sieve elements and “companion ceils”. In climbing species of G. montanum, secondary growth initiates in s normal manner which is followed by the development of new combium at various loci among the parenehyms cells towards the periphery of each bundle. It does not initiate from the phloem parenchyma which is in agreement with the findings of Pearson (1929) and Maheshwari etc. (1961). Gradually these loci become incorporated into a continuous cylinder, producing a normally oriented ring of xylem and phloem separated by broad medullary rays. The growth of the first ring ceases at the commencement of the further formation of the outer, successive rings.     

A novel insight into the structure of amphivasal secondary bundles on the example of Dracaena draco L. stem

Key message

Pattern of tracheids found along the bundles extends understanding of their cross - sectional anatomy and sheds a new light on the issue of radial transport in monocotyledons with secondary growth.

Abstract

Secondary growth of Dracaena draco L. stem is connected with the formation of amphivasal vascular bundles in which a centrally located phloem is surrounded by a ring of xylem cells (tracheids). However, as visible in a single transverse section, there is a tendency towards variation among the secondary bundles from such with a xylem ring to ones in which the tracheids do not completely surround the phloem, i.e., are separated by vascular parenchyma cells. We aimed to elucidate the cross-sectional anatomy of amphivasal secondary bundles using the method of serial sectioning (with sections 3 μm thick), which allowed us to follow very precisely the bundle structure along its length. The analysis revealed that the xylem arrangement in these bundles depends on the position of a section in the bundle path. Each amphivasal bundle is composed of sectors where tracheids form a ring, as well as of such where tracheids are separated by vascular parenchyma cells. We hypothesize that this structure of amphivasal vascular bundles facilitates radial transport of assimilates to the sink tissues. The result of the anatomical analysis is discussed in a physiological context.     

Glutamine Transfer from Xylem to Phloem and Translocation to Developing Leaves of Populus deltoides

The distribution of ¹⁴C from xylem-borne [¹⁴C]glutamine, the major nitrogen compound moving in xylem sap of cottonwood (Populus deltoides Bartr. ex Marsh), was followed in rapidly growing shoots with a combination of autoradiographic, microautoradiographic, and radioassay techniques. Autoradiography and ¹⁴C analyses of tissues showed that xylem-borne glutamine did not move with the transpiration stream into mature leaves. Instead, most of it was transferred from xylem to phloem in the upper stem and then translocated to young developing tissues. Microautoradiography showed that metaxylem parenchyma, secondary xylem parenchyma, and rays were the major areas of uptake from xylem vessels in the stem. Accumulation in phloem (high ¹⁴C concentrations in sieve tubes) took place in internodes subtending recently mature leaves. Little ¹⁴C from xylem-borne glutamine was found in phloem of mature leaves, which indicates restricted retransport of glutamine that did enter the leaf. In the primary tissues of the upper stem, most ¹⁴C was found in the phloem. Cottonwood stems have an efficient uptake and transfer system that enhances glutamine movement to developing tissues of the upper stem.     

The electrogenic proton pumping from parenchyma symplast into xylem—direct demonstration by xylem perfusion

Abstract We have devised an experimental system for simultaneous measurement of the activity of the xylem electrogenic ion pump, which is located on the inner cell membrane between the parenchyma symplast (p) and the xylem (x). and pH of the xylem exudate of a hypocotyl segment of Vigna unguiculata under pressurized xylem perfusion. Anoxia caused immediate depolarization of the inner cell membrane followed by alkalization of the xylem exudate several minutes later. Activity of the xylem pump was recovered by reaeration and acidification of the xylem exudate took place. These results indicate that the xylem pump is the respiration-dependent electrogenic proton-pump extruding proton from the parenchyma symplast into the xylem.     

Spatial relation between xylem and phloem in the stem of Hibiscus cannabinus L. (Malvaceae)

The distribution of the phloem in relation to the xylem was examined in the stem of Hibiscus cannabinus L. with reference to a report in the literature that this species has internal (intraxylary) phloem, a feature not previously observed in the Malvaceae. In the present study, the stem was found to have phloem only outside the xylem (external or extraxylary phloem). In the protophloem, the sieve tubes are obliterated while the internode elongates and the associated cells become fibres with thick secondary walls. Fibres occur in the secondary phloem also. As seen in transections of stems, the secondary xylem forms a continuous ring. The primary xylem extends in the form of arcs into the pith. The tracheary cells of the protoxylem become crushed or completely obliterated in elongating internodes. The associated parenchyma cells either retain thin walls or develop secondary thickenings.     

STUDIES OF NECROTIC LESIONS IN CORN STALKS

Littlefield , Larry J., and Roy D. Wilcoxson . (U. Minnesota, St. Paul.) Studies of necrotic lesions in corn stalks . Amer. Jour. Bot. 49(10): 1072–1078. Illus. 1962.—In 3-day-old necrotic lesions in corn stalks caused by Fusarium graminearum, ground parenchyma cells were discolored and small amounts of a dark substance were present in the cells. The walls of phloem cells were also slightly discolored and a small amount of dark substance was present in the xylem cells. In older lesions the discoloration of parenchyma and phloem cells was more intense; many of the cells contained occluding substances; many phloem protoplasts collapsed, and xylem cells were partially to completely occluded. The occluding substance filling the cells appeared to be translocated from the lesion into the vessel elements extending beyond the lesion so that the bundles appeared as long, dark streaks in the stalk. The occluding substance in xylem, but not in phloem or parenchyma, stained with ruthenium red, a result indicating presence of pectin. Pectinase, however, did not remove the occluding substance. The pectinase dissolved the parenchyma cells in healthy tissues but not in the necrotic lesions. Necrosis in naturally infected plants began as small lesions, but the parenchyma cells quickly dissolved leaving the vascular bundles free of ground parenchyma. No occlusions were found in the central vascular system; a few xylem cells in the peripheral vascular system were occluded with the same substance observed in artificially inoculated plants. Phloem was entirely destroyed by the pathogen. The necrosis prevented upward movement of dye solution in the stalk, but did not measurably affect transpiration, probably because the lesions were not large. Yield was reduced in plants when lesions involved more than 50% of the tissue in inoculated internodes. Smaller lesions had no effect on yield.     

远志根的形态发生及组织化学研究

应用植物解剖学方法对远志(Potygda tenuiflia Willd.)根的发生和发育过程,以及1 a生与2 a生根的结构进行了比较观察,还应用组织化学方法对远志根储藏物质及主要药用成分积累部位进行了研究.结果表明:远志的药用部位为其主根,发育过程包括原分生组织、初生分生组织、初生结构和次生结构4个发育阶段.原分生组织来源于胚根,由3群原始细胞组成,具有典型分生组织的细胞学特征;初生分生组织包括根冠原、表皮原、皮层原和中柱原;初生结构由表皮、皮层和维管柱组成,初生木质部为二原型;次生生长主要是依靠维管形成层和木栓形成层的活动来完成.木栓形成层由中柱鞘细胞恢复分裂能力而形成,并且产生多层栓内层薄壁细胞.2 a生远志根的基本结构与1 a生的基本相同,只是栓内层增加至10层以上.远志根的储藏物质主要是脂类物质及少量的多糖.远志皂苷积累在远志根的薄壁细胞中,而山酮类化合物主要分布在根的木栓形成层、栓内层薄壁细胞和次生韧皮部中.     

Anomalous Growth in the Stem of Ipomoea batatas (L.) Lam. Infested with Megastes Larvae

The stem of Ipomoea batatas (L.) Lam. is characterized by thepossession of a ring of bicollateral, leaftrace bundles. Lacticifersoccur in the pith, in the parenchyma between neighbouring islandsof medullary phloem, and in the cortex. The xylem groups become united by the activity of the inter-fascicularcambium. The production of a certain amount of secondary xylemtakes place before the production of secondary phloem begins.The former is produced more extensively in some areas than inothers, so that the original symmetry of the vascular cylinderis lost. The phellogen originates in the cells of the epidermis. When the stem is attacked by the larvae of Megastes grandalisGuen., which remove most of the internal tissues, anomalousgrowth takes place as a result of the activity of accessorycambia, which develop in the primary cortex, the secondary phloem,and the phelloderm. Residual parenchyma of the pith and/or xylemundergoes hyperplasia to produce a callus tissue which linesthe cavity made by the larvae.