Vascularization of the scutellum of wheat

1970 ◽  
Vol 18 (1) ◽  
pp. 45 ◽  
Author(s):  
JG Swift ◽  
TP O'Brien
Keyword(s):  
Vascular System ◽  
Sieve Tube ◽  
Serial Sections ◽  
Phloem Tissue ◽  
Phloem Parenchyma ◽  
Parenchyma Cells ◽  
Single Ring

The pattern of vascularization of the wheat scutellum shortly after germination is reconstructed from serial sections of plastic-embedded specimens. Nearly half of the phloem in the scutellum is unaccompanied by xylem. Most of the phloem tissue consists of distinct strands, composed of a central sieve tube encircled by a single ring of phloem parenchyma cells. The possible functions of this unusual vascular system are discussed in detail.

Elemental Analysis of Phloem Tissue in Lemna Minor Root Tips

1980 ◽  
Vol 38 ◽  
pp. 798-799
Author(s):  
Patrick Echlin ◽  
Thomas Hayes ◽  
Clifford Lai ◽  
Greg Hook
Keyword(s):  
Vascular Tissue ◽  
Lemna Minor ◽  
Atomic Weight ◽  
Companion Cell ◽  
Root Tips ◽  
Phloem Tissue ◽  
Cell Stage ◽  
Phloem Parenchyma ◽  
Parenchyma Cells ◽  
Xylem Element

Studies (1—4) have shown that it is possible to distinguish different stages of phloem tissue differentiation in the developing roots of Lemna minor by examination in the transmission, scanning, and optical microscopes. A disorganized meristem, immediately behind the root-cap, gives rise to the vascular tissue, which consists of single central xylem element surrounded by a ring of phloem parenchyma cells. This ring of cells is first seen at the 4-5 cell stage, but increases to as many as 11 cells by repeated radial anticlinal divisions. At some point, usually at or shortly after the 8 cell stage, two phloem parenchyma cells located opposite each other on the ring of cells, undergo an unsynchronized, periclinal division to give rise to the sieve element and companion cell. Because of the limited number of cells involved, this developmental sequence offers a relatively simple system in which some of the factors underlying cell division and differentiation may be investigated, including the distribution of diffusible low atomic weight elements within individual cells of the phloem tissue.

THE ONTOGENY OF ADVENTITIOUS STEMS ON ROOTS OF CREEPING-ROOTED ALFALFA

1957 ◽  
Vol 35 (4) ◽  
pp. 463-475 ◽  
Author(s):  
Beatrice E. Murray
Keyword(s):  
Vascular System ◽  
Root Culture ◽  
Vascular Tissues ◽  
Phloem Parenchyma ◽  
Root Segments ◽  
Parenchyma Cells ◽  
Ontogenetic Study ◽  
Meristematic Activity

An ontogenetic study of adventitious stem formation on root segments of creeping-rooted alfalfa clones is presented. Unusual meristematic activity is evident first in the phellogen near a lateral rootlet. Continued activity in that region gives rise to a primordial dome from which adventitious stems eventually emerge. Concomitantly, in the subjacent phloem parenchyma cells dedifferentiation and subsequent redifferentiation into vascular tissues occurs. Thus a vascular system is formed which extends from the adventitious stems to the cambium region of the root and, in some instances, to the cambium of the lateral rootlet. Adventitious stems are initiated in secondary tissues of the root. Factors such as age of root, culture treatment, and inherent differences have an influence on adventitious stem initiation.

Structure of Wood and Cambial Variant in the Stem of Dalbergia Paniculata Roxb.

IAWA Journal ◽  
1990 ◽  
Vol 11 (4) ◽  
pp. 379-391 ◽  
Author(s):  
M. N. B. Nair ◽  
H. Y. Mohan Ram
Keyword(s):  
Succinate Dehydrogenase ◽  
Dehydrogenase Activity ◽  
Sieve Tube ◽  
Secondary Phloem ◽  
Succinate Dehydrogenase Activity ◽  
Successive Cambia ◽  
Phloem Parenchyma ◽  
Companion Cells ◽  
Parenchyma Cells ◽  
Cambial Variant

The wood of Dalbergia paniculata is unique as it consists of concentric layers of broad xylem, alternating with bands of narrow phloem. This anomaly results from the periodic formation of successive cambia in the secondary phloem. Some phloem parenchyma cells dedifferentiate to form a discontinuous ring of cambium. Such parenchyma cells have higher succinate dehydrogenase activity than the neighbouring cells of secondary phloem. The newly differentiated cambial layer functions bidirectionally, and its products give rise to xylem internally and phloem externally. The phloem along with cambium present internal to the newly formed xylem becomes included.The wood is diffuse-porous and the intervessel pits are vestured. The phloem has welldifferentiated sieve tube members and companion cells.

Variability of Bark Structure in Plantation-Grown Eucalyptus Globulus

IAWA Journal ◽  
1999 ◽  
Vol 20 (2) ◽  
pp. 171-180 ◽  
Author(s):  
Teresa Quilhó ◽  
Helena Pereira ◽  
Hans Georg Richter
Keyword(s):  
Eucalyptus Globulus ◽  
Sieve Tube ◽  
Variable Number ◽  
Tree Age ◽  
Phloem Parenchyma ◽  
Age Related ◽  
Parenchyma Cells ◽  
Axial Variation ◽  
Bark Structure ◽  
Old Trees

The bark structure of Eucalyptus globulus Labill. grown in plantations in Central Portugal is described, based on specimens extracted at six height levels from ten 15-year-old trees. No significant variation of qualitative features between trees was observed. The non-collapsed phloem is characterised by multiseriate tangential rows of phloem parenchyma alternating with rows of phloem fibres, interspersed with large sieve tubes and their respective companion cells, and uniseriate rays . With the onset of sieve tube collapse (collapsed phloem ), some parenchyma cells expand and sclerify, the course of rays becomes irregular, and ray dilatation is initiated. The periderm is composed of a phellem of lignified cells with horseshoe thickening (phelloids), followed by a layer of cells with suberised tangential walls, and a phelloderm with a variable number of layers of thin-walled cells. Age-related secondary changes give rise to a specific within-tree pattern of axial variation. Both the intensity of sclerification of phloem parenchyma cells and the degree of ray dilatation increase with tree age.

Structure of Stem and Cambial Variant in Spatholobus Roxburgii (Leguminosae)

IAWA Journal ◽  
1993 ◽  
Vol 14 (2) ◽  
pp. 191-204 ◽  
Author(s):  
M.N.B. Nair
Keyword(s):  
Vascular Tissue ◽  
Secondary Growth ◽  
Sieve Tube ◽  
Secretory Cells ◽  
Secondary Phloem ◽  
Phloem Parenchyma ◽  
Companion Cells ◽  
Parenchyma Cells ◽  
Ray Cells ◽  
Cambial Variant

The stern of Spatholobus roxburghii, a tropicalliana, has alternating layers of xylem and phloem as a result of formation and activity of successive cambia. Successive cambial rings are developed by dedifferentiation of groups of parenchyma cells outside the discontinuous band of sclereid-fibres. The sclereid- fibre band is formed by the development of sclereids between the primary bark fibres. Each successive cambium first produces a layer of sclereid-fibres which separates the vascular tissue produced by one cambial ring from the other. After secondary growth, the epidermis is replaced by periderm. In the older stern phelloderm contributes to the formation of new cambiallayers. Secondary phloem has sieve tube members; companion cells, phloem parenchyma, phloem fibres and secretory cells. The wood shows a tendency towards ring-porosity only in the first xylem layer. The subsequent layers are diffuseporous. The vessels are wide and narrow. Perforated ray cells or radial vessels are frequent in the wood and probably help in vertical conduction by interconnecting vessel endings. In this scandent species parenchyma cells are abundant. It is inferred that they help the vessel segments to remain undamaged when the woody stern twists around supports.

The Vascular Structure of the Kidney of Mallards and Doves

1999 ◽  
Vol 5 (S2) ◽  
pp. 1192-1193
Author(s):  
H. Ditrich
Keyword(s):  
Vascular System ◽  
Venous Drainage ◽  
Portal System ◽  
Physiological Data ◽  
Vascular Structure ◽  
Serial Sections ◽  
Functional Importance ◽  
Additional Material ◽  
Functional Studies ◽  
Primitive Feature

The architecture of the kidney of birds (and also reptiles) is, unlike in mammalians, mainly determined by the organization of the blood vascular system. Besides arterial supply and venous drainage, the renal portal system forms a main structural component. While the latter was often regarded as a “primitive” feature in the literature, morphological and physiological data reveal its great functional importance.Microvascular corrosion casts studied in the scanning electron microscope permit the visualization of minute vessels, retaining their 3D-arrangement. Additionally, when compared with graphical reconstructions of serial sections, this method avoids several inherent artifacts like fixation and dehydration shrinkage as well as the compression of the object by the sectioning blade. Most of the studies on avian kidneys with this technique used the domestic chicken as a model. In order to provide additional material for comparative and functional studies, data on the intrarenal vascular structure of other species are required.

scholarly journals THE FINE STRUCTURE AND DEVELOPMENT OF THE COMPANION CELL OF THE PHLOEM OF ACER PSEUDOPLATANUS

1965 ◽  
Vol 24 (1) ◽  
pp. 117-128 ◽  
Author(s):  
F. B. P. Wooding ◽  
D. H. Northcote
Keyword(s):  
Endoplasmic Reticulum ◽  
Sieve Tube ◽  
Acer Pseudoplatanus ◽  
Sieve Plate ◽  
Wheat Grain ◽  
Companion Cell ◽  
Large Nucleus ◽  
Cell Organelles ◽  
Phloem Tissue ◽  
Aleurone Cells

At maturity the companion cell of the phloem of the sycamore Acer pseudoplatanus has a large nucleus, simple plastids closely sheathed with rough endoplasmic reticulum, and numerous mitochondria. The cytoplasm contains numerous ribosomes, resulting in a very electron-opaque cytoplasm after permanganate fixation. Bodies similar to the spherosomes of Frey-Wyssling et al. (4) are collected in clusters and these also contain bodies of an unidentified nature similar to those found by Buttrose (1) in the aleurone cells of the wheat grain. The pores through the wall between the companion cell and sieve tube are complex and develop from a single plasmodesma. Eight to fifteen plasmodesmata on the companion cell side communicate individually with a cavity in the centre of the wall which is linked to the sieve tube by a single pore about twice the diameter of an individual plasmodesma. This pore is lined with material of an electron opacity equivalent to that of material bounding the sieve plate pores. The development of the cell organelles, the possible role played in the phloem tissue by the companion cell, and the function of the complex pores contained in its wall are discussed.

The secondary phloem of Austrobaileya scandens

1970 ◽  
Vol 48 (2) ◽  
pp. 341-359 ◽  
Author(s):  
Lalit M. Srivastava
Keyword(s):  
Tannic Acid ◽  
Cross Sections ◽  
Significant Proportion ◽  
Sieve Tube ◽  
Secondary Phloem ◽  
Sieve Elements ◽  
Sieve Cells ◽  
Companion Cells ◽  
Parenchyma Cells ◽  
Definition Of

The origin of sieve elements and parenchyma cells in the secondary phloem of Austrobaileya was studied by use of serial cross sections stained with tannic acid – ferric chloride and lacmoid. In three important respects, Austrobaileya phloem recalls gymnospermous features: it has sieve cells rather than sieve-tube members; a significant proportion of sieve elements and companion cells arise independently of each other; and sieve areas occur between sieve elements and companion cells ontogenetically unrelated to each other. The angiospermous feature includes origin of most sieve elements and parenchyma, including companion cells, after divisions in phloic initials. In these instances companion cells show a closer ontogenetic relationship to sieve elements than do other parenchyma cells. The combination of gymnospermous and angiospermous features makes phloem of Austrobaileya unique when compared to that of all those species that have been investigated in detail. It is further suggested that the term albuminous cells is inappropriate and should be replaced by companion cells but that the ontogenetic relationship implicit in the definition of companion cells is too restrictive and should be abandoned.

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