DEVELOPMENTAL ANATOMY IN ROOTS OF IPOMOEA PURPUREA. II. INITIATION AND DEVELOPMENT OF SECONDARY ROOTS

In seedlings of Ipomoea purpurea secondary roots are initiated in the primary root pericycle opposite immature protoxylem. Cells derived from immature endodermis, pericycle, and incipient protoxylem and stelar parenchyma contribute to the primordium. The derivatives of the endodermis become a uniseriate covering over the tip and flanks of the primordium and emerged secondary root; the endodermal covering is sloughed off when the lateral root reaches 1–5 mm in length. A series of periclinal and anticlinal divisions in the pericycle and its derivatives gives rise to the main body of the secondary root. The initials for the vascular cylinder, cortex, and rootcap-epidermis complex are established very early during primordium enlargement. After emergence from the primary root, the cortical initials undergo significant structural modifications related to enlargement of the ground meristem and cortex, and the rootcapepidermal initials are partitioned into columellar initials and lateral rootcapepidermal initials. Procambium diameter increases by periclinal divisions in peripheral sectors. The mature vascular cylinder is comprised of several vascular patterns, ranging from diarch to pentarch, that are probably related ontogenetically. Cells derived from incipient protoxylem and stelar parenchyma cells of the primary root form the vascuar connection between primary and secondary roots.     

OBSERVATIONS ON THE ROOT ANATOMY OF RICE (ORYZA SATIVA L.)

Rice plants were grown hydroponically and roots were prepared for light and electron microscopy using standard techniques. The roots are bounded by an epidermis, exodermis, and fibrous layer. The exodermis has a suberin lamella along its inner tangential wall. The fibrous layer is composed of thick-walled lignified cells with little pitting. The cortical parenchyma is compact when young, but expands and separates to form a zone of cell walls and air spaces in a spoked arrangement. Supporting columns of living parenchyma cells are occasionally present, particularly near lateral roots. The endodermis is typical for grasses with Casparian strips, suberin lamellae, and tertiary state walls with numerous pits. The pericycle and pith become sclerified. Protoxylem elements alternate with protophloem in the young root; later, early metaxylem, late metaxylem, and metaphloem proliferate. The exodermis, fibrous layer, lacunate cortex, and endodermis appear to present a formidable barrier to radial ion movement in the mature portions of the root.     

Chemical Composition of the Epidermal, Hypodermal, Endodermal and Intervening Cortical Cell Walls of Various Plant Roots

A survey of chemical modifications in the cells of the epidermis,hypodermis, cortical parenchyma and endodermis in roots of 27plant species was performed. Cortical parenchyma walls weregenerally free of modifying substances whereas the walls ofthe epidermis, hypodermis and endodermis were usually modifiedby the presence of lipids, phenols, suberin or lignin. In mostcases, wall-modifying components could be detected within 5mm of the root apex. lipids, phenols, suberin, lignin, ferulic acid, root, epidermis, hypodermis, cortex, endodermis, cell wall     

Cluster root development in Grevillea robusta (Proteaceae). II. The development of the endodermis in a determinate root and in an indeterminate, lateral root

Light, fluorescence and electron microscopy were employed to follow the development of the endodermis in cluster roots and lateral roots of Grevillea robusta A. Cunn. ex R. Br. Endodermal cells had three different origins: rootlet endodermis arose from the rootlet meristem; endodermis covering the primordium shortly after initiation came from division of parental endodermis; cells at the junction between parent and rootlet endodermis developed from re-differentiated rootlet cortical cells. In the cluster root, the Casparian band formed in three ways, and was not initially present opposite the two sets of single xylem elements in the rootlet stele. A new clearing technique was developed that allowed visualization of xylem, suberized endodermis, Casparian band formation and phenolic compounds. In lateral roots, endodermal differentiation was asynchronous, but was related to position relative to protoxylem poles. However, the observed delay began before these poles had differentiated. At the tip of mature rootlets, which are determinate, the endodermis terminates in a 'dome' of cells, with the initial cell differentiating as an endodermal cell. Results are discussed in terms of determinate development in roots and the spatial and temporal contexts within which this development takes place.     

Ultrastructure of the haustorial interface and apoplastic continuum between host and the root hemiparasiteOlax phyllanthi (Labill.) R. Br. (Olacaceae)

Summary Structural features of haustorial interface parenchyma of the root hemiparasiteOlax phyllanthi are described. Walls contacting host xylem are thickened non-uniformly with polysaccharides, not lignin, and show only a thin protective wall layer when abutting pits in walls of host xylem vessels or tracheids. Lateral walls of interface parenchyma exhibit an expanded middle layer of open fibrillar appearance, sometimes with, but mostly lacking adjoining layers of dense wall material. Free ribosomes and rough endoplasmic reticulum are prominent and occasional wall ingrowths present. Experiments involving transpirational feeding of the apoplast tracers lanthanum nitrate or uranyl acetate to host roots cut below haustorial connections, indicate effective apoplastic transfer from host to parasite root via the haustorium. Deposits of the tracers suggest a major pathway for water flow through host xylem pits, across the thin protective wall layer, and thence into the haustorium via the electronopaque regions of the terminal and lateral walls of the contact parenchyma. Graniferous tracheary elements and walls of parenchyma cells of the body of the haustorium appear to participate in tracer flow as do walls of cortical cells, stele parenchyma and xylem conducting elements of the parasite root, suggesting that both vascular and non-vascular routes are involved in extracytoplasmic transfer of xylem sap from host to parasite. The Casparian strip of the endodermis and the suberin lamella of the exodermis of theOlax root act as barriers to flow within the system.     

SEEDLING GROWTH AND ROOT CONTRACTION IN THE SOAP PLANT,CHLOROGALUM POMERIDIANUM (LILIACEAE)

Radicles and adventitious roots of the soap plant are contractile and through their activity, mature bulbs of this species are buried to depths of 20–30 cm. Experiments were performed to determine rates of contraction and displacement of the shoot apex resulting from activity of the contractile radicle and the first several adventitious roots. The average displacement was 23.2 mm over a 10-wk period and 63.8 mm over 29 weeks. Small glass beads and abortive seeds served as controls and showed no displacement through the soil column. Measurements from longitudinal and transverse sections of contracted and uncontracted portions of radicles revealed average increases of 26–64% in radial dimensions and 40–56% decreases in longitudinal dimensions of inner and middle cortical cells (excluding the endodermis) following contraction. Cells of the outermost cortex (excluding the exodermis) decreased in average longitudinal dimensions by 18–26% before becoming distorted and collapsed as contraction was completed. Average volumes of innermost cortical cells decreased by 15–54%, while two or three cell layers of the middle cortex, adjacent to collapsed outer cortical cells, increased in volume up to 75%. These middle cortical cells are identified as the “active” cells which, by their growth, are responsible for the shortening of the root. Throughout the process of contraction, the stele remains straight and undistorted, although the closer spacing of tracheary element secondary wall thickenings following contraction suggests longitudinal compression of the stele. The average number of cortical cells per transverse section does not differ in contracted and uncontracted roots and no evidence is found to support the “interdigitation” hypothesis of root contraction. However, reorientation of middle cortical cell expansion may be the mechanism of root contraction in Chlorogalum pomeridianum.     

THE ROOT APEX OF MALVA SYLVESTRIS. III. LATERAL ROOT DEVELOPMENT AND THE QUIESCENT CENTER

Both histological and autoradiographic procedures were used to follow lateral root initiation and development. Lateral roots of M. sylvestris were initiated in the pericycle, and although the endodermis became multiseriate, endodermal derivatives were not incorporated into the lateral root primordium. Apical organization of pre-emergent roots, characterized by two tiers of cortical initials, did not change with growth. During pre-emergent development there was no evidence of cortical lysogeny or quiescent center formation. Quiescent centers were present in both secondary and tertiary roots longer than 0.5 cm.     

Chimeras and the Origin of Lateral Root Primordia in Zea mays

The difficulty of determining the contribution made by the pericycleand endodermis of mother roots to lateral primordia in the Gramineaehas been solved by inducing polyploid chimeras at initiation. The endodermis forms a layer covering the primordium, but thislayer does not form the epidermis of the lateral. It does formthe root cap of the young primordium, but this is replaced ata variable stage of development by the quiescent centre donatinga new set of cap initials of pericyclic origin. Reasons forthe previous diversity of interpretations are presented. chimera, lateral root primordia, Zea mays     

The Behaviour of Two Cell Populations in the Pericycle of Allium cepa, Pisum sativum, and Daucus carota During Early Lateral Root Development

The length of cells of the pericycle, endodermis and middlecortex not actively involved in lateral root primordia (LRP)development was measured in primary roots of Allium cepa, Pisumsativum and Daucus carota. The presence of two cell populationsin the pericycle was demonstrated in all three species. In Alliumcepa and Pisum sativum, pericyclic cells located opposite xylempoles were significantly shorter than cells lying opposite phloempoles. In both species, LRP originated opposite xylem poles.Our results, furthermore, strongly suggest that in regions ofthe root far from the apical meristem, numerous pericyclic cellsundergo transverse division both previous to and during LRPinitiation, decreasing in mean length throughout this period.In Daucus carota, LRP begin to form in pericyclic cells locatednext to the phloem poles, such cells were significantly shorterthan those opposite xylem poles, even in areas of the primaryroot located close to the root tip. Cells also appear to dividetransversely in regions far from the root tip in this species,leading to a conspicuous drop in the mean length of those cellslocated in portions of the pericycle destined to give rise toLRP. Two different cell populations can also be distinguishedin the endodermis of Allium cepa and Pisum sativum, althoughobservations were less conclusive in Daucus carota. In all threespecies, length of cortical cells was unaffected by their positionopposite xylem or phloem poles Allium cepa, carrot, cell division, cell length, Daucus carota, endodermis, lateral root development, onion, pea, pericycle, Pisum sativum     

珍稀植物扇脉杓兰营养器官的解剖学研究

采用石蜡切片技术对扇脉杓兰营养器官的解剖结构进行了研究。结果表明：根状茎的薄壁细胞中含丰富的淀粉粒,维管柱中分布着排列紧凑的周木维管束;根的皮层发达,有的皮层细胞中存在真菌菌丝团,木质部与韧皮部呈辐射状相间排列,根和根状茎的内皮层细胞都形成马蹄形加厚结构。茎的表面分布气孔,皮层面积较小,皮层内部的基本组织发达,外韧维管束散生分布其中,茎和叶上都附有非腺性毛;叶为等面叶,叶肉细胞排列疏松,气孔主要分布于远轴面,略外凸,保卫细胞中含有叶绿体,叶缘处的叶肉组织中含有气腔结构。扇脉杓兰营养器官的这些特征与其荫蔽湿润的生境是相适应的。     

The root-tuber anatomy of Asphodelus aestivus

The root tubers of Asphodelus aestivus consist mostly of enlarged fleshy storage tissue. They are bounded by a multiple-layered velamen, responsible for rapid water uptake, water loss reduction, osmotic and mechanical protection. In the cortex area, thin-walled idioblasts contain numerous raphides of calcium oxalate in their large vacuole with a distinctive tonoplast. Wide morphological variations are observed among the raphide cross sections. Electron-dense compounds penetrate the raphide surface and raphide groove. Raphides seem to be vital for the protection of the root tuber parenchyma from herbivores. The cells of uniseriate endodermis are heavily thickened possessing a few plasmodesmata. The vascular cylinder is 20–28-arch and the root xylem consists of vessels in short radial rows, alternating with clusters of phloem cells. The presence of cells, which contain soluble polysaccharides in their large vacuole, is conspicuous after employing the Schiff's reagent. Exodermis cells and all cell walls, especially the thick ones of the endodermis, are also stained. Numerous parenchyma cells, especially those around vascular bundles are stained intensely, when exposed to Sudan Black B. These cells occurring as solitary idioblasts abundantly accumulate oil. Electron-dense remnants are evident within the vacuoles of the storage cells especially near the vascular tissue. The morphological features of A. aestivus root tubers and the major part of the total plant biomass are responsible for the species’ occurrence and frequent dominance in a wide array of arid environments. A. aestivus possessing root tubers is proved to be very efficient in storing water during the long summer drought, less susceptible to climatic stress and well synchronized with the climatic fluctuations of the Mediterranean environment.     

Embryogenesis in Najas marina L.: Structural and histochemical approach

In Najas marina L. few polysaccharide grains are observed in zygote, basal cell and embryonal cells until the initiation of embryonic shoot-apex. With the formation of the shoot-apex, numerous polysaccharide grains engorge in the embryonal cells. The basal cell wall, subjacent to the nucellus, stains intensely with PAS (Peiodic Schiff's)-reaction. The concentration of proteins and RNA increases in the basal cell.Interestingly, the embryo shows intraseminal germination. The cells of embryonic shoot-apex, embryonic leaves, root primordium and procambial cells show a few polysaccharide grains while the cells of hypocotyledonary and cotyledonary regions are engorged with polysaccharide (starch) grains. Uniform distribution of proteins and RNA is observed in the embryonic shoot-apex, embryonic-leaves, root primordium and procambium, but the cells of hypocotyledonary and cotyledonary zones exhibit a low profile for these metabolites. The initial root-primordium remains quiescent. Three or 4 epidermal cells, subjacent to this quiescent primordium, differentiate; show densely stained, polarised, protein bands; and act as the future root primordium.The nucleus of the basal cell becomes polyploid and densely stains for proteins, RNA and DNA. At the globular proembryo stage, numerous nucleolar bodies migrate towards the periphery of the nucleus and at the 3-leaf embryo stage, these nucleolar bodies, rich in proteins and RNA, are located in the cytoplasm revealing nucleo-cytoplasmic interaction. The basal cell that never divides, but only enlarges, is persistent in the mature seed.     

Cortical Air Spaces (Aerenchyma) in Roots of Corn Subjected to Oxygen Stress: STRUCTURE AND INFLUENCE ON UPTAKE AND TRANSLOCATION OF RUBIDIUM IONS

When the seminal root system of 14-day-old corn (Zea mays cv. Dekalb 202) was subjected to O₂ stress, nodal roots with well developed cortical air spaces (aerenchyma) grew into the deoxygenated solution. Microscopic examination showed that there was extensive breakdown of cells in the midcortex of these roots, while the stele, endodermis, and inner layer of cortical cells remained complete, as did the outer layers of the cortex and the epidermis. Occasional files of intact cells, and the wall residues of collapsed cells, crossed the space between inner and outer cortex. Experiments with short, intact root segments with and without air spaces showed that in the presence of O₂ the ability to absorb and translocate ⁸⁶Rb⁺, per unit volume or length of root, was little affected by cortical degeneration. The distribution across root sections of recently supplied strontium and rubidium, determined by electron microprobe analysis, indicated that in roots with air spaces the strands of wall residues bridging the cortex could be involved in maintaining the conduction of ions from the outer cortex up to the endodermis.     

Tissue-6

In order to study a possible involvement of cdc-like proteinkinases in cell development and tissue differentiation, a polyclonalantibody raised against the evolutionary conserved PSTAIR-regionof p34^cdc2-homologue protein kinases (PSTAIR-proteins) was appliedto sections of the maize root apices. PSTAIR-proteins were localizedin the nuclei and the cytoplasm of cells in the root meristem,including the quiescent centre (QC), and of all dividing cellsthat form the lateral root primordia. In most root tissues,the amount of cytoplasmic PSTAIR-proteins progressively declinedwith increasing distance from the root cap junction, becomingrestricted to the nucleus after the cessation of cell divisions.This occurred much nearer to the root cap junction in cellsof the stele, especially in metaxylem cells, than in cells ofthe root cortex. Interesting exceptions were cells of the pericycle,endodermis and the outermost cell rows of stelar parenchyma,which exhibited relatively high levels of the cytoplasmic PSTAIR-proteinsthroughout all developmental zones. After root wounding, rapid cytoplasmic accumulation of PSTAIR-proteinsin cells adjacent to the wound was observed in all tissues ofthe meristem and of the elongation zone. This wound response,which was usually followed by newly-induced cell divisions,was delayed with increasing distance from the root cap junctionin a tissue-specific manner. Since PSTAIR-proteins were foundin the cell nuclei throughout all developmental zones, theyseem to have some nuclear functions which continue even aftercell division has stopped. Key words: Cell cycle, maize roots, cyclin-dependent protein kinases, wounding     

Zostera capensis setchell: Root structure in relation to function

Root structure of the seagrass Zostera capensis Setchell was investigated by light and electron microscopy. Roots possess conspicuous root hairs which greatly increase the surface area available for absorption. Exodermal cells abutting root-hair bases possess transfer cell characteristics. The strategic location of these cells suggests that they participate in absorptive and/or transfer processes between the epidermis and cortex. Vascular parenchyma cells within the stele also possess transfer cell features. Wall ingrowths of these cells about xylem elements, sieve tubes, companion cells and other vascular parenchyma cells, suggesting that they play a role in absorptive and/or transfer processes between the stele and cortex. Apoplastic barriers in the form of suberin lamellae and Casparian bands occur in walls of both the exodermis and endodermis. However, plasmodesmata perforate the suberin lamellae in these walls, and a symplastic pathway can be traced from the root hairs to vascular parenchyma transfer cells contiguous with conducting elements of the stele. The occurrence of wall ingrowths adjacent to xylem elements implies that transfer processes occur between vascular transfer cells and xylem. Although reduced, xylem could therefore play a role in transport. Structural evidence obtained in this study supports the role of the roots in absorptive processes and shows pathways available for transport from the water column to the conducting tissues of the root.     

Ultrastructural Pathology of Cells Affected by Pratylenchus penetrans in Alfalfa Roots

Cortical parenchyma cells penetrated and fed upon by Pratylenchus penetrans for 48 hours contained only cytoplasmic debris. Proximal cells had an increase in tannin deposits, degenerated mitochondria, increased numbers of ribosomes, and no internal membrane structure. Often the endodermis was collapsed and contained massive tannin deposits on the inner cell wall and cell lumen. Similar observations were made in the stele, except tannin deposits were not as prominent. Multivesicnlate structures were observed both in the endodermis and in the stele.     

加兰他敏在忽地笑营养器官中的定位(简报)

石蒜属植物为具有地下鳞茎的多年生草本植物．有重要的药用价值,全属植物约有20余种。我国有石蒜属植物约15种,集中分布于长江中下游地区,野生资源比较丰富。忽地笑（Lycorisaurea Herb．）是石蒜属植物在我国分布较广泛的一种。加兰他敏（Galanthamine）等生物碱是石蒜属植物中主要的药用成分。[第一段]